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Why cannot there be multiple sources for same species origins?


We often associate Africa as the geographical location of the origin of humans. Why cannot there exist multiple geographic locations of origin (given same environmental conditions)?

The same argument exists for other species as well. So what is the basis of the common ancestor (from single geographical location) theory?

Please give me references so that I can read more on this subject.


This is a very fundamental, and in my opinion, interesting question. You might not find many sources that directly cover this question because it is hard to test. If speciation did happen in two separate locations and the resulting species were so similar that they could breed with one another and not the original species, how would we be able to tell if the species originated in separate locations and that the new species didn't just travel to the new location? Below I'll try and explain why it's safe to assume they probably didn't have different locations for speciation.

Thought Experiment

Here is what happened in hypothetical land. Species X exists in happy land. Individuals of X then move to water land. Some more individuals from X move from happy land to H2O land (very similar to water land). Species X undergoes speciation in water land to species Y and speciation of X also occur in the H2O land to species Z.

Can Z and Y be the same species with different origins where the niche conditions are the same?

As you can imagine, the longer after geographical isolation the more mutations occur and the less likely it is that the new species will be able to breed successfully with similar species.

Although the two environments may seem identical, ecology is notoriously complex and chaotic, and so in reality as far as ecology is concerned, they are very different environments. Even the slightest difference between niches will naturally select different traits that could make Z and Y sexually incompatible.

Furthermore, when dealing with the geographical origin, you must assume that there was geographical isolation between the two speciation event locations. Since there is typically no contact between Z and Y species, there is no selective pressure to remain genetically compatible and given enough time, they will become unable to breed.


Humans

There is a contentious claim that ancient humans bred with chimpanzees after both speciation events from our common ancestor to humans and chimpanzees. Broadly I think this has now been dismissed. However, it is reasonably well accepted that in a more recent "Tolkien-esque" world humans bred with Neanderthals.

But ultimately I don't think there is a single example (I am thoroughly open to being proven wrong!) in the natural world of two similar geographical isolation events driving exactly the same species to evolve and both versions of the new species are more genetically similar to one another than they are to the origin species. The odds are just too slim even if to us the conditions seem identical.


References - Wiki article about the theory of multiregional origin for humans. The wiki article clearly states up front that this is "an alternative explanation to the more widely accepted Out of Africa model". One issue brought up in this article, is although there doesn't seem to be any unique localized single feature, there has been unique combinations of localized features found in early fossils in locations like Australia. The wiki article includes further references.

http://en.wikipedia.org/wiki/Multiregional_origin_of_modern_humans

The more accepted theory is "Out of Africa". Wiki articles:

http://en.wikipedia.org/wiki/Out_of_Africa_I

http://en.wikipedia.org/wiki/Recent_African_origin_of_modern_humans

http://en.wikipedia.org/wiki/Early_human_migrations

Another article that explains why "Out of Africa" is the more accepted theory:

http://www.actionbioscience.org/evolution/johanson.html

Note that all of this is with respect to modern humans. I don't know if there are any animals or plants where multiple source for the same species is the more accepted theory.

Hybrids (the offspring of two compatible, but different species parents) could occur if the parents where multi-regional. You can do a web search for polyploid hybrids and tree frog for examples of this, but these are hybrids, not mutations.


No single birthplace of mankind, say scientists

A replica skull of a Homo naledi: Various locations vie for the title of ‘cradle of mankind’ or the ‘source of humanity’, but new research says this is not the case. Photograph: Gulshan Khan/AFP/Getty Images

A replica skull of a Homo naledi: Various locations vie for the title of ‘cradle of mankind’ or the ‘source of humanity’, but new research says this is not the case. Photograph: Gulshan Khan/AFP/Getty Images

Last modified on Wed 11 Jul 2018 16.12 BST

The origins of our species have long been traced to east Africa, where the world’s oldest undisputed Homo sapiens fossils were discovered. About 300,000 years ago, the story went, a group of primitive humans there underwent a series of genetic and cultural shifts that set them on a unique evolutionary path that resulted in everyone alive today.

However, a team of prominent scientists is now calling for a rewriting of this traditional narrative, based on a comprehensive survey of fossil, archaeological and genetic evidence. Instead, the international team argue, the distinctive features that make us human emerged mosaic-like across different populations spanning the entire African continent. Only after tens or hundreds of thousands of years of interbreeding and cultural exchange between these semi-isolated groups, did the fully fledged modern human come into being.

Dr Eleanor Scerri, an archaeologist at Oxford University, who led the international research, said: “This single origin, single population view has stuck in people’s mind … but the way we’ve been thinking about it is too simplistic.”

This continental-wide view would help reconcile contradictory interpretations of early Homo sapiens fossils varying greatly in shape, scattered from South Africa (Florisbad) to Ethiopia (Omo Kibish) to Morocco (Jebel Irhoud).

From L to R : Fossil skull of Homo neanderthalis, Homo antecessor, Homo sapiens and Homo erectus Photograph: Creativemarc/Getty Images

The telltale characteristics of a modern human – globular brain case, a chin, a more delicate brow and a small face – seem to first appear in different places at different times. Previously, this has either been explained as evidence of a single, large population trekking around the continent en masse or by dismissing certain fossils as side-branches of the modern human lineage that just happened to have developed certain anatomical similarities.

The latest analysis suggests that this patchwork emergence of human traits can be explained by the existence of multiple populations that were periodically separated for millennia by rivers, deserts, forests and mountains before coming into contact again due to shifts in the climate. “These barriers created migration and contact opportunities for groups that may previously have been separated, and later fluctuation might have meant populations that mixed for a short while became isolated again,” said Scerri.


Anatomy and Embryology

Another type of evidence for evolution is the presence of structures in organisms that share the same basic form. For example, the bones in the appendages of a human, dog, bird, and whale all share the same overall construction ([Figure 2]). That similarity results from their origin in the appendages of a common ancestor. Over time, evolution led to changes in the shapes and sizes of these bones in different species, but they have maintained the same overall layout, evidence of descent from a common ancestor. Scientists call these synonymous parts homologous structures. Some structures exist in organisms that have no apparent function at all, and appear to be residual parts from a past ancestor. For example, some snakes have pelvic bones despite having no legs because they descended from reptiles that did have legs. These unused structures without function are called vestigial structures . Other examples of vestigial structures are wings on flightless birds (which may have other functions), leaves on some cacti, traces of pelvic bones in whales, and the sightless eyes of cave animals.

Figure 2: The similar construction of these appendages indicates that these organisms share a common ancestor.

Click through the activities at this interactive site to guess which bone structures are homologous and which are analogous, and to see examples of all kinds of evolutionary adaptations that illustrate these concepts.

Another evidence of evolution is the convergence of form in organisms that share similar environments. For example, species of unrelated animals, such as the arctic fox and ptarmigan (a bird), living in the arctic region have temporary white coverings during winter to blend with the snow and ice ([Figure 3]). The similarity occurs not because of common ancestry, indeed one covering is of fur and the other of feathers, but because of similar selection pressures—the benefits of not being seen by predators.

Figure 3: The white winter coat of (a) the arctic fox and (b) the ptarmigan’s plumage are adaptations to their environments. (credit a: modification of work by Keith Morehouse)

Embryology, the study of the development of the anatomy of an organism to its adult form also provides evidence of relatedness between now widely divergent groups of organisms. Structures that are absent in some groups often appear in their embryonic forms and disappear by the time the adult or juvenile form is reached. For example, all vertebrate embryos, including humans, exhibit gill slits at some point in their early development. These disappear in the adults of terrestrial groups, but are maintained in adult forms of aquatic groups such as fish and some amphibians. Great ape embryos, including humans, have a tail structure during their development that is lost by the time of birth. The reason embryos of unrelated species are often similar is that mutational changes that affect the organism during embryonic development can cause amplified differences in the adult, even while the embryonic similarities are preserved.


2. The African middle�rly late Pleistocene fossil record of Homo sapiens

The fossil record available to reconstruct the evolution of H. sapiens in Africa is still relatively sparse and poorly dated, and is dominated by material from the fossiliferous sedimentary basins of East Africa. Huge expanses of Central and West Africa were clearly inhabited during the later middle Pleistocene, as shown by the evidence of artefacts, but not a single informative fossil has yet been recovered to identify who those early inhabitants were. Thus, the available record is probably highly biased and unrepresentative of the continent as a whole. Nevertheless, we have to work with what is available, and I will now briefly discuss the most complete or significant specimens discovered so far, region by region ( figureਁ ). Wider and more detailed compilations on the material and its dating can be found in Schwartz & Tattersall [32], Millard [33], Klein [34] and Wood [35].

Left lateral views of African and Israeli archaic and early modern Homo sapiens crania (replicas unless otherwise stated). Top (L to R): Florisbad, Jebel Irhoud 1, Jebel Irhoud 2 (original), Eliye Springs, Guomde (reversed), Omo 2. Bottom (L to R): Omo 1, Herto (original, reversed), Ngaloba, Singa, Skhul 5, Qafzeh 9.

(a) North-west and North Africa

In Morocco, the later middle Pleistocene archaeological record probably changes from non-Aterian Middle Palaeolithic/Middle Stone Age (MSA) industries to those of the Aterian during Marine Isotope Stage (MIS) 6, although it seems likely that a non-Aterian MSA continues in some regions alongside and even after the Aterian [36,37].

The Jebel Irhoud cave was exposed during quarrying operations in a Baryte mine and since 1961 has produced faunal remains, non-Aterian MSA archaeology and at least seven fossil hominins, with several more specimens found since 2007 awaiting publication. The fossil human remains are from low in the stratigraphic sequence, the best known being a cranium (JI1), a calvaria (JI2) and the mandible of a child (JI3) [38]. The cranium is relatively long and low with smooth rather than angular contours. It has a strong continuous supraorbital torus anterior to a somewhat domed frontal, and parallel-sided cranial vault with a capacity of about 1305 cm 3 [39]. The face is large and especially broad in its upper dimensions, with flat angled cheekbones and a broad but low nose, below which is significant alveolar prognathism. JI2 is a somewhat larger, more robust and angular calvaria, with a cranial capacity of approximately 1400 cm 3 [39]. It has a greater occipital projection and angulation, more modern parietal and frontal shape, but equally strong supraorbital development. Although comparisons of midline contours suggest H. sapiens affinities for both cranial vaults, multivariate studies indicate somewhat closer affinities for JI2 to recent human samples [40,41]. Both display some phenetic resemblances to early modern specimens such as those from Qafzeh, Skhul and Herto, though they lack their upper parietal expansion. In cranial vault (but not facial) form, there is nevertheless an overall resemblance to the Sima fossils and other early Neanderthals. The JI3 immature mandible presents a rather contrasting gracile body and large posterior teeth, and anteriorly may show incipient chin development. JI4 is a robust partial humerus, despite its immaturity, while there is also a further immature pelvic fragment. Overall, there is enough preserved of JI1 to indicate that it does not represent anatomically modern H. sapiens, although there are hints of ‘modern’ basicranial flexion in the relationship of the face and vault. JI2 and 3 are more difficult to assess because of their incompleteness, but the teeth of Irhoud 3 were subjected to synchrotron analysis which suggested an age at death of about 8 years, and a modern developmental pattern [42]. At the same time, an ESR analysis of its tooth enamel suggested an age of approximately 160 ka, which seems very likely to be a minimum figure.

The Rabat (Kebibat) hominin from Morocco consists of a very fragmentary cranial vault with more complete upper and lower jaws. The large teeth are typical of middle Pleistocene specimens from North Africa, but the mandible has elements of a mental trigone and a vertical symphysis, while the occipital region is high and relatively rounded [38]. However, the individual is subadult and so caution must be exercised in interpreting its morphology. Faunal correlation places the Rabat specimen in the late middle Pleistocene.

The Moroccan cave of Dar-es-Soltan II has produced an immature calvaria, an adolescent mandible and the anterior part of a skull with associated hemimandible. The anterior vault of DeS5 is high and very large, with a strong but divided supraorbital torus over a low, broad and flat face, with a low but broad nose. There are indications of a canine fossa and of alveolar prognathism. The mandible and the preserved posterior dentition are also large, but illustrations are deceptive in indicating the lack of a chin—the symphysial region is in fact broken off. Deciding on how to classify DeS5 is difficult—it has a rather modern-looking face and frontal bone shape, but both are very large in size, as is the supraorbital development. Although previous assessments have suggested that it could represent an Aterian intermediate between the MSA-associated Irhoud specimens and those of the Iberomaurusian (i.e. local late Upper Palaeolithic), morphometric analyses place it closer to Jebel Irhoud 1 and the Qafzeh crania than to the late Pleistocene fossils [36].

The caves of El-Aliya and Témara (Morocco) have produced fragmentary human cranial fossils from MSA/Aterian contexts. The Aliya material includes a large maxilla and teeth, but despite previous assertions, the preserved cheek morphology seems rather flat and non-Neanderthal [43]. However, not enough is preserved for definitive statements about the affinities of the material. The Témara specimens consist of some vault fragments, lacking a supraorbital torus and a mandible, which can more definitely be allied with modern H. sapiens.

A number of other Aterian sites have produced dental material which was analysed by Hublin et al. [43]. The cave of Zouhrah at El Harhoura yielded a mandible and canine during excavations in 1977, while the Grotte des Contrabandiers (Temara) has been under intermittent excavation since 1955 with early discoveries of material such as a robust and large-toothed mandible (in 2009 a still-unpublished immature human skeleton was recovered from Aterian levels apparently dated to MIS5). The Aterian dental samples generally display very large dimensions compared with late Pleistocene H. sapiens and Neanderthals. However, a relatively smaller anterior dentition and thicker enamel on the molars are more modern traits. While crown morphologies are generally complex, they resemble material like Skhul and Qafzeh more closely in pattern than the Neanderthals.

In contrast to the large and complex molar morphology found in the Moroccan Aterian material, the only teeth in the posterior mandible fragments recovered from ‘levalloiso-mousterian’ deposits in the Libyan cave of Haua Fteah in the 1950s are small and simple-crowned. The mandible fragments both have rather low rami and no evidence of retromolar spaces. As far as can be judged from the limited morphology preserved, these appear to represent H. sapiens, with an age now estimated at approximately 70 ka, within the early part of MIS4 [44]. Another possibly MSA-associated specimen which lacks the dental size and complexity of the Moroccan Aterian material is the cranium and fragmentary skeleton of a child recovered within sand deposits on the top of Taramsa Hill, Egypt [45]. Enough of the cranial vault is preserved to indicate a modern shape, even before cleaning, but the postcranial skeleton was highly friable and little of it survives. The MSA age of the specimen could not be definitively confirmed by direct dating [46].

(b) Southern Africa

The Florisbad 𠆌ranium’ (in fact only the anterior part of a skull and face) was found at this open locality in South Africa in 1932, stratified in a long sequence which remained poorly dated until 1996, when ESR on an enamel fragment from the human fossil provided an age estimate of approximately 259 ka [47]. The frontal bone is wide, thick and relatively receding, and the supraorbital torus is high but not strongly projecting, with lateral reduction. The face is incomplete but is certainly very broad in its upper proportions, with some expression of a canine fossa. In R. Clarke's reconstruction, it is low relative to its great breadth, but allowing for a complete anterior dentition, as in P. Cohen's unpublished reconstruction ( figureਁ ), it may well have been closer to the Broken Hill cranium in facial height. Florisbad has sometimes been seen as morphologically allied to Broken Hill, at other times as an early member of the H. sapiens clade, and at yet other times as possibly representing a distinct late Middle Pleistocene species H. helmei, either a precursor species to H. sapiens [48], or as the LCA of the Neanderthal and modern clades, and the originating species of Mode 3 (levallois) lithic technology [49]. While too incomplete for definitive assignment, like the Irhoud material this fossil probably represents an archaic part of the H. sapiens clade.

The Klasies River Mouth fossil human material has been recovered over a period of more than 40 years in a variety of MSA-related stratigraphic contexts from an interrelated complex of caves on the southern coast of South Africa [34]. The material is fragmentary and represents mandibular, maxillary, facial, cranial vault and postcranial elements. The mandibles display great variation, ranging from large and chinless through ones with an apparently modern symphysial morphology, to a very small, albeit robust corpus with tiny teeth. Two maxillary fossils show comparable variation in size, while an isolated zygomatic is robust but of modern aspect, despite claims to the contrary. An apparently adult frontal fragment displays a wide interorbital breadth but centrally has a modern supraorbital profile. The few recovered postcranial bones indicate small-bodied individuals, although a proximal ulna has relatively large joint surfaces. Some elements of the Klasies assemblages clearly conform to the modern H. sapiens pattern, but other material cannot be so readily assigned on the parts preserved.

Border Cave, South Africa, has produced a number of fossil or subfossil human remains of actual or possible MSA antiquity [50]. In the 1940s, a humerus, ulna fragment and two metatarsals were recovered out of context in a spoil heap but have been argued on preservation grounds to be of MSA age. Their size and robusticity suggest that they might represent the same individual as the Border Cave 1 partial skull also found in spoil. This ‘skull’ actually consists of only part of the upper face and vault, but enough is preserved to show its large size, domed frontal, small supraorbital development and wide interorbital breadth. Although it appears of modern aspect, its large size and frontal and upper facial shape discriminate it from recent populations, and the possibly associated humerus and ulna display a few archaic traits. An edentulous mandible (BC2) recovered around the same time is small and more lightly built and appears assignable to anatomically modern H. sapiens on size and symphysial morphology. The infant skeleton BC3 certainly appears to represent H. sapiens, and has an important association with perforated Conus shells and red pigment [51]. Like BC2, the BC5 partial mandible is small and has a modern symphysial morphology, and its importance has been enhanced by direct ESR dating, providing an age estimate of approximately 74 ka [50].

(c) East Africa

The Eliye Springs (ES-11693) cranium was discovered by tourists after rapid changes in lake levels at West Turkana, Kenya [52]. The cranium had suffered anterior erosion, particularly of the face, but enough is preserved to reveal an archaic morphology. The vault is long and inferiorly broad, with limited upper parietal expansion, parallel-sided in rear view. There is slight frontal keeling but cranial buttressing is not strongly expressed, although it is not possible to assess the full extent of supraorbital torus development due to erosion, which has exposed the frontal sinuses. The occipital contour is rather rounded with minimal development of an occipital torus. Although heavily eroded, the face appears to resemble some late middle Pleistocene African crania in being relatively short, flat and broad, and there are signs of the slight development of a canine fossa. Although ES-11693 was discovered with faunal remains, the lack of any secure context or associated archaeology means that it remains undated. What is preserved of the specimen does not suggest particular H. sapiens affinities, although there are regional characteristics in facial shape and vault form that may relate it to other middle Pleistocene African crania such as Florisbad, Jebel Irhoud 1, Singa and Ngaloba. However, like Singa (see below, this section) its shape may have been affected by pathology [53].

Seven fragmentary cranial and mandibular fossils have been recovered from sediments bordering Lake Eyasi in Tanzania since the 1930s. Possible association with Acheulian artefacts had suggested an earlier rather than later middle Pleistocene age, but limited ESR and U-series age estimates from fauna associated with frontal 7 suggest an age approximately between 88 and 130 ka. Eyasi 1 has a projecting but not massive supraorbital torus on its frontal, while its occipital is more modern in torus formation compared with a much stronger development in Eyasi 2, even displaying a possible suprainiac fossa. Frontal 7, like Eyasi 1, shows a rather low frontal bone with a distinct but not massive torus. The fragmentary condition of the material and difficulties of reconstruction limit the information available beyond indications that these specimens are apparently not assignable to anatomically modern H. sapiens [54,55], despite the later Pleistocene date suggested for some of them.

Ngaloba Laetoli Hominid 18 was recovered from the Ngaloba beds in the Laetoli region of Tanzania [56]. This partial cranium may date from the late middle or early late Pleistocene [57]. It is relatively long and low with an elongated and receding frontal bone. It is rather rounded posteriorly in both rear and lateral views, with negligible development of an occipital torus, but anteriorly there is a prominent but thin supraorbital torus. The occipitomastoid region is interesting for its resemblance to that of Neanderthals in the relation of mastoid and juxtamastoid eminences. The face cannot be properly articulated with the vault, but it is evidently rather low, broad and flat in the midface, with canine fossae, giving way to a prognathic subnasal region. The reconstruction by Cohen [58] confirms the relative gracility of the face, but suggests a greater height than in other depictions. Workers such as Rightmire [59] have classified LH18 as fundamentally modern, but it does not conform to anatomically modern H. sapiens in overall morphology, despite a suggestive facial and parietal shape.

Three Omo Kibish fossil hominins were discovered in 1967 in separate localities and contexts. Omo 1 was a partial skeleton in Member I of the Kibish Formation, Omo 2 an isolated surface find of a calvaria and Omo 3 a frontal fragment from member III [60]. More recently, an American-led expedition has located the original sites of Omo 2 and Omo 1, recovering more human material, including further parts of Omo 1, and additional fossils [61,62]. The fragmented skull from the Omo 1 assemblage has been the subject of several reconstructions but all concur in indicating a high, rounded and voluminous cranial vault with an occipital morphology of sapiens configuration, albeit with a wide frontal bone and strong but partitioned brow ridges. The face, dentition and mandible are much more fragmentary but evidence a canine fossa and mental eminence [63]. The postcranial remains include fragmentary limb bones which are largely of modern aspect, although with some distinctive features also noted in Neanderthal, Skhul-Qafzeh and Upper Palaeolithic individuals [61], and with proportions comparable with those of recent East Africans [64]. Omo 2 also has a very large braincase, with an endocranial capacity of approximately 1435 cm 3 , but is narrower, with parallel-sided rather than superiorly expanded parietals, and a strongly angled occipital bone bearing a high but not especially projecting occipital torus. It also displays parasagittal flattening either side of a midline keel. In contrast with these archaic features, the supraorbital torus is a weakly expressed prominence at the anterior end of a flat, broad and receding frontal bone. The ages of Omo 1 and 2 have been sources of much controversy, but now seem well established at approximately 195 ka [17,65]. Classifying the Omo material is difficult. It is evident that Omo 1 can be assigned to modern H. sapiens from the preserved parts, but Omo 2 can only be tentatively placed in the clade through the apomorphy of supraorbital reduction.

The two separate human fossils found in the Guomde Formation of East Turkana in 1971 and 1976 consist of a proximal femur fragment KNM-ER 999 and a partial skull KNM-ER 3884 [66]. The femur is strongly built but seemingly of modern aspect in shaft shape and cross section [67] while the partial skull seems to combine characteristics found in Omo Kibish 1 and 2. It is similarly large and high, with a rounded modern-looking occipital region like Omo 1, but looking much more like Omo 2 in rear profile, high, with vertical walls. The supraorbital torus, as reconstructed, is evenly thick and projecting. Direct uranium-series dating of the material suggests an age of more than 180 ka [68].

Several cranial and dental human fossils were recovered from an open site at Herto in Ethiopia in 1997 [69]. The most significant consist of a nearly complete adult skull, an immature calvaria and parts of another cranial vault, probably adult. All are very large in size, the adult skull having a capacity of approximately 1450 cm 3 . The length of the skull is outside the range of over 5000 modern crania, but its high and relatively globular shape (except for the occipital) conforms to the H. sapiens pattern. The supraorbital torus is strong and projecting, although divided into lateral and central parts, but the angled occipital with its centrally strong torus is reminiscent of that of Broken Hill 1 and Jebel Irhoud 2. The rear of the separate cranial fragments indicates an even greater size and robusticity than the most complete cranium. Univariate and multivariate analyses showed that the combination of features of the adult skull differentiate it from recent humans, but in terms of cranial shape, cranial angles and neurocranial globularity, it can be classified as H. sapiens, perhaps of comparable grade to material from Qafzeh & Skhul [70]. Its modernity was reaffirmed in metrical studies by Lubsen & Corruccini [71] and McCarthy & Lucas [72]. However, the addition of the subspecific nomen idaltu [69] does not seem justified.

The Singa calvaria was discovered in a block of calcrete in the seasonally dry bed of the Blue Nile in Sudan in 1924. It was notable for its strong parietal bosses, which were argued by some workers to link it to Khoisan origins, despite its great distance from southern Africa [73]. It has a well marked but centrally divided supraorbital torus, flat upper face and wide interorbital spacing, while the frontal is quite high. However, the parietals are very short and the occipital is also short and protruding, without showing a transverse torus. Natural breakage allowed removal of calcrete filling the endocranium, revealing the parietal bosses were abnormally thickened by diploic bone. An endocranial mould indicated a cranial capacity of about 1400 cm 3 , while its asymmetry suggested a left-handed individual [74]. CT-scanning revealed further evidence of pathology in the unilateral absence of the inner ear on the right side, and Spoor et al. [75] suggested labyrinthine ossification had occurred, following an infection of the labyrinth membrane. This may have been due to a blood-borne infection (such as septicaemia) or a blood disorder such as anaemia, which fits with some explanations for the parietal pathology. Because of its pathology, it is unclear how abnormal is the shape of the calvaria. Overall, the anterior cranial morphology looks fairly modern, but the parietals are abnormal, preventing proper taxonomic assessment. The fossil is dated to a minimum age of 131� ka by U-series dating on sediments from the inside of the calvaria, and ESR analyses on associated faunal remains [76].

(d) Western Asia (Skhul and Qafzeh)

Although not in Africa, the adjacent Levant has clearly been a conduit for ancient population movement between Africa and Eurasia. Material such as the Zuttiyeh fronto-facial fragment, probably from the middle Pleistocene, remains difficult to classify, but in my view it does not show clear Neanderthal or modern human affinities, as can also be argued for the approximately 400 ka dental sample from Qesem [77]. Later and more clearly diagnosable material usually assigned to MIS5 also comes from Israel, in the form of the Tabun 1 Neanderthal skeleton, and the material I will discuss in more detail from the caves of Skhul and Qafzeh.

The site of Mugharet es-Skhul comprises a small cave, and a larger external rock-shelter and terrace, with most of the archaeological and hominin remains coming from the latter. The Skhul fossils, comprising 10 individuals, were discovered by Ted McCown in 1931� as part of a larger rescue dig in the Mount Carmel area directed by Dorothy Garrod [78]. There is evidence that at least some of the Skhul individuals were intentionally buried [79], which may explain their relatively good preservation. Skhul 4 and 5 have significant portions of cranial and postcranial material preserved, while Skhul 9 consists of a more fragmentary calvaria and face with fragments of the pelvis and a femur. At one stage, Skhul was believed to be only around 40 ka in age, based on faunal and lithic similarities to Tabun, the Middle Palaeolithic levels of which had supposedly been dated to about 40 ka using radiocarbon. However, the Skhul material (Skhul 2, 5 and 9) has now been dated to between approximately 100 and 130 ka using ESR, U-series and luminescence analyses [80]. Nevertheless, it remains possible that Skhul 9 is older than the other fossils, as suggested by its morphology and lower stratigraphic position [48,80].

The first discoveries from Qafzeh Cave and its terrace (including Qafzeh 6) were made in the 1930s, but the full study and publication of the Qafzeh specimens only really began in the 1970s, by which time new excavations were greatly enlarging the Middle Palaeolithic-associated sample to 16 individuals. Vandermeersch's monographic work on the still-growing series [81] demonstrated that the Skhul and Qafzeh samples shared Middle Palaeolithic associations, the apparent presence of symbolic burials, and significant skeletal similarities. In terms of morphology, Vandermeersch highlighted the H. sapiens (sensu stricto) affinities of both groups of hominins from their cranial and mandibular shape to their pelves and limb bones. Non-metric, metric and morphometric analyses have regularly supported the view that the cranial, dental and postcranial anatomy of the combined Skhul-Qafzeh sample represents an early form of H. sapiens sensu stricto, albeit with robust or primitive features (e.g. [82�]). As with Skhul, the application of luminescence, ESR and U-series dating has also placed the Middle Palaeolithic material into MIS5, with age estimates ranging approximately from 90 to 120 ka [89].

While the Skhul and Qafzeh series show clear derived traits in cranial and postcranial anatomy shared with Upper Palaeolithic and recent humans, they also display considerable variation, and differ in aspects of cranial shape and morphology, both within and between the samples (e.g. [3,48]). Given the wide error ranges on the available physical dating of the sites and skeletal and archaeological material [57], it is currently impossible to determine whether the Skhul and Qafzeh specimens represent different samples from essentially the same variable MIS5 population, as is often assumed in palaeoanthropological studies, two distinct populations, perhaps separated by many millennia, or even a sample of hominins covering a long period of time at both sites.


Cutting down the tree

The complexity of our evolutionary picture has led many researchers to recently move away from the idea that we emerged from a single locale that branched outward into a global family tree. Instead, they suggest our species evolved from many points across Africa, like a network or braided stream with many inputs, divergences, and some rejoining rivulets that leads to the mighty mix flowing through our veins.

“I don’t see any reason, really, to be wedded to any particular place,” says Thomas, a co-author of a recent paper that challenged a single origin for our species.

The new study’s authors acknowledge that our species could have arisen from multiple origins. But there’s not yet enough data to definitively show that’s the case, says study co-author Eva Chan, a statistical geneticist at the Garvan Institute of Medical Research. And the latest work was a cross-disciplinary attempt to fill some blanks in the picture of our evolutionary history.

“That’s not to say we have the picture right now,” she says. “With more data, the picture will continue to change.”

All of this work also circles the increasingly confusing definition of a species. While humans like to put everything in boxes, nature doesn’t fit into tidy categories, Schlebusch says. There are no distinct lines between one species and the next everything works in shades of gray.

The controversy over our origins will surely continue. Unlike many fields of study, human evolution is not something you can design experiments to test, Akey adds. But then again, perhaps scientists need to rethink the debate entirely.

“Maybe the question we’re asking isn’t the right one,” he adds. “Maybe we need a more nuanced question.”


Extreme Competition and Cannibalism

Intraspecific competition often works by the adage "desperate times call for desperate measures." Sharks are a good example of this phenomenon, because during times of especially scarce food resources, sharks resort to the ultimate form of competition: cannibalism. Instead of competing with other species for new food resources, sharks simply start to eat each other. Other animals, such as rodents, exhibit this behavior more regularly, with mothers often eating their young. This happens because they foresee scarce food resources, and know they cannot adequately provide for the food of their young. While most animals try to avoid cannibalism, extreme times often reduce them to the act, and this sometimes even includes humans.


"Origin of Species" is published

On the Origin of Species by Means of Natural Selection, a groundbreaking scientific work by British naturalist Charles Darwin, is published in England. Darwin’s theory argued that organisms gradually evolve through a process he called “natural selection.” In natural selection, organisms with genetic variations that suit their environment tend to propagate more descendants than organisms of the same species that lack the variation, thus influencing the overall genetic makeup of the species.

Darwin, who was influenced by the work of French naturalist Jean-Baptiste de Lamarck and the English economist Thomas Malthus, acquired most of the evidence for his theory during a five-year surveying expedition aboard the HMS Beagle in the 1830s. Visiting such diverse places as the Galapagos Islands and New Zealand, Darwin acquired an intimate knowledge of the flora, fauna, and geology of many lands. This information, along with his studies in variation and interbreeding after returning to England, proved invaluable in the development of his theory of organic evolution.

The idea of organic evolution was not new. It had been suggested earlier by, among others, Darwin’s grandfather Erasmus Darwin, a distinguished English scientist, and Lamarck, who in the early 19th century drew the first evolutionary diagram𠅊 ladder leading from one-celled organisms to man. However, it was not until Darwin that science presented a practical explanation for the phenomenon of evolution.

Darwin had formulated his theory of natural selection by 1844, but he was wary to reveal his thesis to the public because it so obviously contradicted the biblical account of creation. In 1858, with Darwin still remaining silent about his findings, the British naturalist Alfred Russel Wallace independently published a paper that essentially summarized his theory. Darwin and Wallace gave a joint lecture on evolution before the Linnean Society of London in July 1858, and Darwin prepared On the Origin of Species by Means of Natural Selection for publication.


There’s No Scientific Basis for Race—It's a Made-Up Label

It's been used to define and separate people for millennia. But the concept of race is not grounded in genetics.

In the first half of the 19th century, one of America’s most prominent scientists was a doctor named Samuel Morton. Morton lived in Philadelphia, and he collected skulls.

He wasn’t choosy about his suppliers. He accepted skulls scavenged from battlefields and snatched from catacombs. One of his most famous craniums belonged to an Irishman who’d been sent as a convict to Tasmania (and ultimately hanged for killing and eating other convicts). With each skull Morton performed the same procedure: He stuffed it with pepper seeds—later he switched to lead shot—which he then decanted to ascertain the volume of the braincase.

Morton believed that people could be divided into five races and that these represented separate acts of creation. The races had distinct characters, which corresponded to their place in a divinely determined hierarchy. Morton’s “craniometry” showed, he claimed, that whites, or “Caucasians,” were the most intelligent of the races. East Asians—Morton used the term “Mongolian”—though “ingenious” and “susceptible of cultivation,” were one step down. Next came Southeast Asians, followed by Native Americans. Blacks, or “Ethiopians,” were at the bottom. In the decades before the Civil War, Morton’s ideas were quickly taken up by the defenders of slavery.

“He had a lot of influence, particularly in the South,” says Paul Wolff Mitchell, an anthropologist at the University of Pennsylvania who is showing me the skull collection, now housed at the Penn Museum. We’re standing over the braincase of a particularly large-headed Dutchman who helped inflate Morton’s estimate of Caucasian capacities. When Morton died, in 1851, the Charleston Medical Journal in South Carolina praised him for “giving to the negro his true position as an inferior race.”

Today Morton is known as the father of scientific racism. So many of the horrors of the past few centuries can be traced to the idea that one race is inferior to another that a tour of his collection is a haunting experience. To an uncomfortable degree we still live with Morton’s legacy: Racial distinctions continue to shape our politics, our neighborhoods, and our sense of self.

This is the case even though what science actually has to tell us about race is just the opposite of what Morton contended.

The Surprising Way Saliva Brought These Six Strangers Together

Morton thought he’d identified immutable and inherited differences among people, but at the time he was working—shortly before Charles Darwin put forth his theory of evolution and long before the discovery of DNA—scientists had no idea how traits were passed on. Researchers who have since looked at people at the genetic level now say that the whole category of race is misconceived. Indeed, when scientists set out to assemble the first complete human genome, which was a composite of several individuals, they deliberately gathered samples from people who self-identified as members of different races. In June 2000, when the results were announced at a White House ceremony, Craig Venter, a pioneer of DNA sequencing, observed, “The concept of race has no genetic or scientific basis.”

Over the past few decades, genetic research has revealed two deep truths about people. The first is that all humans are closely related—more closely related than all chimps, even though there are many more humans around today. Everyone has the same collection of genes, but with the exception of identical twins, everyone has slightly different versions of some of them. Studies of this genetic diversity have allowed scientists to reconstruct a kind of family tree of human populations. That has revealed the second deep truth: In a very real sense, all people alive today are Africans.

Our species, Homo sapiens, evolved in Africa—no one is sure of the exact time or place. The most recent fossil find, from Morocco, suggests that anatomically modern human features began appearing as long as 300,000 years ago. For the next 200,000 years or so, we remained in Africa, but already during that period, groups began to move to different parts of the continent and become isolated from one another—in effect founding new populations.

In humans, as in all species, genetic changes are the result of random mutations—tiny tweaks to DNA, the code of life. Mutations occur at a more or less constant rate, so the longer a group persists, handing down its genes generation after generation, the more tweaks these genes will accumulate. Meanwhile, the longer two groups are separated, the more distinctive tweaks they will acquire.

By analyzing the genes of present-day Africans, researchers have concluded that the Khoe-San, who now live in southern Africa, represent one of the oldest branches of the human family tree. The Pygmies of central Africa also have a very long history as a distinct group. What this means is that the deepest splits in the human family aren’t between what are usually thought of as different races—whites, say, or blacks or Asians or Native Americans. They’re between African populations such as the Khoe-San and the Pygmies, who spent tens of thousands of years separated from one another even before humans left Africa.

All non-Africans today, the genetics tells us, are descended from a few thousand humans who left Africa maybe 60,000 years ago. These migrants were most closely related to groups that today live in East Africa, including the Hadza of Tanzania. Because they were just a small subset of Africa’s population, the migrants took with them only a fraction of its genetic diversity.

Somewhere along the way, perhaps in the Middle East, the travelers met and had sex with another human species, the Neanderthals farther east they encountered yet another, the Denisovans. It’s believed that both species evolved in Eurasia from a hominin that had migrated out of Africa much earlier. Some scientists also believe the exodus 60,000 years ago was actually the second wave of modern humans to leave Africa. If so, judging from our genomes today, the second wave swamped the first.

In what was, relatively speaking, a great rush, the offspring of all these migrants dispersed around the world. By 50,000 years ago they had reached Australia. By 45,000 years ago they’d settled in Siberia, and by 15,000 years ago they’d reached South America. As they moved into different parts of the world, they formed new groups that became geographically isolated from one another and, in the process, acquired their own distinctive set of genetic mutations.

Most of these tweaks were neither helpful nor harmful. But occasionally a mutation arose that turned out to be advantageous in a new setting. Under the pressure of natural selection, it spread quickly through the local population. At high altitudes, for instance, oxygen levels are low, so for people moving into the Ethiopian highlands, Tibet, or the Andean Altiplano, there was a premium on mutations that helped them cope with the rarefied air. Similarly, Inuit people, who adopted a marine-based diet high in fatty acids, have genetic tweaks that helped them adapt to it.

Sometimes it’s clear that natural selection has favored a mutation, but it’s not clear why. Such is the case with a variant of a gene called EDAR (pronounced ee-dar). Most people of East Asian and Native American ancestry possess at least one copy of the variant, known as 370A, and many possess two. But it’s rare among people of African and European descent.


Common Ancestry and Natural Selection in Darwin’s Origin

This is a précis of an argument that I developed in an article called “Did Darwin Write the Origin Backwards?” The article was published in 2009 and may be found on my web set at http://philosophy.wisc.edu/sober/recent.html. An expanded version of the argument is the first chapter of a book that I’m publishing at the end of 2010 with Prometheus Books. The book has the same title as the 2009 article.

Although Darwin’s theory is often described as the theory of evolution by natural selection, most commentators recognize that common ancestry (the idea that all organisms now alive on earth and all present day fossils trace back to one or a few “original progenitors”) is an important part of the Darwinian picture. What has been less explored in Darwin studies is how these two parts of Darwin’s theory – common ancestry and natural selection — are related to each other. Ernst Mayr and others have noted that they are logically independent. But this leaves open how the two ideas are evidentially related. How does common ancestry affect the way in which evidence concerning natural selection should be evaluated? And how does natural selection affect the way in which evidence concerning common ancestry should be evaluated?

Darwin addresses one of these two questions very succinctly in a passage from the Origin:

… adaptive characters, although of the utmost importance to the welfare of the being, are almost valueless to the systematist. For animals belonging to two most distinct lines of descent, may readily become adapted to similar conditions, and thus assume a close external resemblance but such resemblances will not reveal – will rather tend to conceal their blood-relationship to their proper lines of descent.

The fact that human beings and monkeys have tailbones is evidence for common ancestry precisely because tailbones are useless in humans. Contrast this with the torpedo shape that sharks and dolphins share this similarity is useful in both groups. One might expect natural selection to cause the torpedo shape to evolve in large aquatic predators whether or not they have a common ancestor. This is why the adaptive similarity is almost valueless to the systematist who is trying to reconstruct patterns of common ancestry.

In this passage, Darwin is saying that to determine whether a trait shared by two species is strong evidence that they have a common ancestor, one must be able to judge whether there was selection for the trait in the lineages leading to each. In this sense, knowledge of natural selection is a prerequisite for interpreting evidence concerning common ancestry. However, there is a subtly different question that has a very different answer. Must natural selection have been an important influence on trait evolution for there to be strong evidence for common ancestry? Darwin’s answer to this question is no. A world in which organisms are saturated with neutral and deleterious similarities, while adaptive similarities are rare or non-existent, would be an epistemological paradise so far as the hypothesis of common ancestry is concerned. That’s the point that Darwin is making in the passage I just quoted. Inferring common ancestry does not require that natural selection has occurred.

What about the converse question – how does the fact of common ancestry affect the interpretation of evidence for natural selection? One of Darwin’s most famous arguments concerning natural selection does not depend one whit on common ancestry. This is Darwin’s Malthusian argument. If reproduction in a population outstrips the supply of food, the population will be cut back by starvation. If the organisms in the population vary with respect to characteristics that affect their ability to survive, and if offspring inherit these fitness-affecting traits from their parents, the population will evolve. The process of natural selection is a consequence of these conditions and it can and will occur even if no two species have a common ancestor.

All this is correct, but there is more to the Darwinian picture of natural selection than this. The Malthusian argument establishes that selection has occurred – that some traits changed frequency because of their influence on the viability of organisms. But which traits evolved by natural selection? Darwin doesn’t think that every trait we observe evolved because there was selection for it recall his comment in the Origin that selection is “the main but not the exclusive cause” of evolution. And if a trait did evolve under the influence of natural selection, why was it favored by natural selection? It is these questions, which concern the detailed application of the hypothesis of natural selection to examples, that common ancestry helps to answer.

An interesting illustration of how Darwin uses the assumption of common ancestry to think about natural selection may be found in his discussion of why mammals in utero have skull sutures that allow them to pass through the birth canal:

The sutures in the skulls of young mammals have been advanced as a beautiful adaptation for aiding parturition [live birth], and no doubt they facilitate, or may be indispensable for this act but as sutures occur in the skulls of young birds and reptiles, which have only to escape from a broken egg, we may infer that this structure has arisen from the laws of growth, and has been taken advantage of in the parturition of the higher animals.

On the face of it, Darwin’s reasoning here is odd. If he wants to evaluate the hypothesis that mammals have skull sutures because this facilitates live birth, why does he consider the fact that nonmammals have the sutures but not the live birth? Let us hope that he isn’t thinking that if a trait T evolved because the trait facilitated X in one lineage, that T cannot be present without X in any organisms on earth. Penguins do not refute the hypothesis that wings evolved to facilitate flight in birds. And the hypothesis that a species of lizard evolved its green coloration because this color provided camouflage does not require that every green organism on earth gains protective coloration from its being green.

What Darwin is doing in this and in other similar passages is exploiting the fact of common ancestry to test hypotheses about natural selection. The reason that birds and reptiles are relevant to the question of why mammals have skull sutures is that all these organisms share a common ancestor. Common ancestry allows Darwin to infer what happened in the lineage leading to modern mammals. The fact that present day birds and reptiles have sutures but no live birth is evidence that sutures were present in the lineage leading to modern mammals before live birth evolved. If so, the sutures did not evolve because they facilitated live birth. On the contrary, live birth evolved after the sutures were already in place.

Darwin does not spell out the details of this inference, but modern evolutionary biologists will recognize it as an application of the principle of parsimony. Consider the phylogenetic tree shown in the accompanying figure. The tips of the tree represent modern mammals, reptiles, and birds. This is not the tree that a modern biologist would draw, but it may well have been the one that Darwin thought is true. As you move down the page, you are moving from present to past. The lines represent lineages when two of them coalesce, you have reached a common ancestor. The tree says that mammals and birds are more closely related to each other than either is to reptiles A2 is an ancestor of the first two, but not of the third. If you go sufficiently far into the past, you will find a common ancestor (A1) that unites all three of these present day groups.

The figure also indicates the traits (±skull sutures ± live birth) that contemporary mammals, birds and reptiles exhibit. Given this tree, and the features exhibited by its tips,

what is the most reasonable inference concerning the characteristics of the ancestors A1 and A2? The most parsimonious inference is that A1 and A2 both have skull sutures but no live birth. This is the most parsimonious reconstruction in the sense that it requires fewer changes in character states in the lineages leading to the present than any other reconstruction. If this most parsimonious reconstruction is correct, we can deduce that skull sutures evolved before live birth made its appearance in the lineage leading to modern mammals the mammalian lineage is represented in the figure by a broken line. This parsimony argument justifies Darwin’s statement that sutures now facilitate, or may even be indispensible for, live birth in mammals, but this is not why the sutures evolved.

The argument just described raises an interesting philosophical question: why should we think that the principle of parsimony is a good inferential rule? Why should we think that the most parsimonious hypothesis is true? I won’t pursue this enticing question here. Rather, the point of relevance is that in Darwin’s theory, and in the evolutionary biology of the present, common ancestry is not an unrelated add-on that supplements the hypothesis of natural selection. Instead, common ancestry provides a framework within which hypotheses about natural selection can be tested. In Darwinian biology, a lineage is like a mineshaft that extends from the surface of the earth to deep below, with multiple portholes connecting surface to shaft at varying depths. By peering into a porthole, we gain evidence about what is happening in the shaft. The more portholes there are, the more evidence we can obtain. Thanks to common ancestry, facts about the history of natural selection become knowable.

There is an asymmetry in how common ancestry and natural selection are related to each other in Darwin’s theory. To get evidence for common ancestry, natural selection need not have caused any of the traits we now observe. But to get evidence for natural selection, Darwin needs to be able to think of present day organisms as tracing back to common ancestors. Selection doesn’t make adaptations out of nothing adaptations are modifications of the traits of ancestors. To know what those ancestors were like, we need to be able to infer their characteristics from what we now observe. It is common ancestry that makes those inferences possible.

If this is the right picture of how common ancestry and natural selection are related in Darwin’s theory, a puzzle presents itself: why did Darwin write the Origin by front-loading natural selection? Darwin does mention some ideas about common ancestry early in the book, but the big picture of there being one tree of life for the whole living world emerges only gradually, and later. On the whole, it is natural selection that comes first. Why is the book structured like this? Why didn’t Darwin begin by defending the idea of common ancestry and then gradually introduce natural selection as a secondary theme?

13 comments to Common Ancestry and Natural Selection in Darwin’s Origin

Elliott is right: from an evidential point of view it appears as though Darwin wrote the Origin backwards. It seems that Darwin should have first made the case that evolution has in fact occurred and that the history of life has a tree structure. Then natural selection could take the stage to explain some of the patterns in the history of life. This not only makes sense evidentially, but also rhetorically, since it introduces the explanandum before the explanans: Natural selection is a mechanism that explains patterns of evolutionary change, but before we know that there are such patterns, we have little incentive to accept a mechanism that is supposed to explain them.

However, I think that there are very good reasons why Darwin begins with selection and only then argues for the tree of life. The most convincing kind of argument is often one that begins with an observation that is indisputable, and then leads, through small and innocuous steps, to the desired conclusion. It is precisely this strategy that Darwin employs in the Origin. This approach was particularly important in the historical context in which Darwin developed his ideas. The tree of life was a hard pill to swallow for Darwin’s contemporaries: the geological record was spotty and the patterns of traits across extant organisms would not readily convince many that all life evolved from one or a few progenitors. Darwin knew that his many of his readers would be unable to accept the notion of the tree of life unless it were preceded by the concept of natural selection.

To ready his contemporaries for accepting the tree of life, Darwin needed to establish three key premises: (1) evolution by natural selection occurs and can create varieties, (2) these varieties form lineages, and (3) there is no fundamental difference between varieties and species. To establish (1), he begins with artificial selection and the fact that humans have precipitated change in domesticated animals through generations of selective breeding. This is the evolution via selection that all of his contemporaries would be familiar with, even if they had not conceived of it as such. Artificial selection is often accomplished with a conscious goal of change in mind, as in the case of the pigeon fancier, who might desire a long beak in one of its varieties, and therefore allow only the longest beaked individuals of that variety to breed. Darwin thus led his readers to contemplate a pigeon tree of life, formed via evolution by artificial selection. But to establish (1), he has to replace artificial selection with natural selection. He does this with an ingenious use of an intermediate step, “unconscious selection.”

Although the pigeons were selected consciously, Darwin points out that evolution by artificial selection can occur unconsciously as well. A farmer might merely want his sheep to be maintained as good stock, and selects for breeding what are deemed good, healthy individuals. No new traits are the desired outcome, but nonetheless sheep on different farms will diverge because of this selection process. It is then a small step for Darwin to lead the reader to the idea that natural selection is just like unconscious selection, except that the environment is the sole selector, not, as in the case of the sheep, the environment plus the farmer. The formation of varieties by natural selection, (1), is then established. And it is not too much of a leap to see that just as sheep and pigeons form lineages with progenitors, so can wild animals.

Given (1) and (2), Darwin would have been able to make the case that varieties could be formed in the wild via natural selection. But he had not yet shown how species could evolve. He knew that many of his contemporaries would be able to accept the formation of varieties, but would balk at the idea of naturally produced species. Interestingly, Darwin made the case for naturally produced species by arguing that a species is not an objectively real biological category—he aimed to show that a given taxonomy is as much a result of the inclinations of the taxonomists as it is natural divisions in the world. Genera are not different in kind from species and species are not different in kind from varieties (3). He did so by citing the divergent taxonomies: “few well-marked and well-known varieties can be named which have not been ranked as species by at least some competent judges” (1859, pg. 47).

With (1) – (3) established, Darwin makes it at least conceivable that lineages of species can form via the process of natural selection. It is then that the stage is set for his argument for the tree of life.

Today, with radiometric dating techniques and fossils like Tiktaalik, solid arguments for the tree of life can be made in the absence of natural selection. Had Darwin access to these data, perhaps he would have followed Elliott’s suggestion of presenting the case for the tree of life first. But without such an evidential foundation, Darwin had to ready his readers for what would otherwise seem too great a leap of faith.

Like Grant Ramsey, I am less perplexed by the structure of Darwin’s Origin than Elliot Sober is. Indeed, I suspect that Sober’s puzzles about the order in which natural selection and common ancestry are discussed are in part an artifact of an equivocation on “natural selection.” I will, anyway, try to explain how I see matters, and to do this I need to make a pair of distinctions: the terms “theory of evolution” and “natural selection” both require disambiguation.
First, we need to expose a common equivocation (one not made in Sober’s essay) on “evolutionary theory.” In the Origin, Darwin really put forward two things that are commonly referred to as the theory of evolution. On the one hand, Darwin presents the theory of evolution as a theory that explains the origin of species. This theory is a theory of a single thing, a complex historical event in which one or a few original life-forms diversified and branched out to produce the manifold different species that have arisen in the Earth’s history. This theory is like the theory of continental drift, which equally posits a complex, temporally attenuated process with lots of moving parts that eventuates in a particular distribution of masses on the surface of the planet. The Big Bang theory of the origin of the universe is another similar sort of theory. Call this theory of evolution TOE1. TOE1 is not Darwin’s idea several other thinkers (Lamarck, Chalmers, Darwin’s grandfather) had undertaken it, though none had defended it nearly as well as Darwin does in the Origin.
The other thing commonly called “evolutionary theory” that Darwin puts forward in the Origin, something that is Darwin’s idea (though Wallace thought it up, too), is a theory of the dynamics of a subset of natural systems. This is what is presented in the first few chapters of the Origin. Systems that meet certain specifications, their members exhibit heritable variations and struggle for existence, are governed by this theory, call it TOE2. TOE2 allows us to draw conclusions about the dynamics of the systems it governs, typically that individuals in the system with heritable variations more conducive to survival and reproduction will spread at the expense of those with less adaptive variations. Unlike TOE1, which is about a single complex process, TOE2 is a general theory, one that applies to any system with the right features. Indeed, as advocates of Universal Darwinism have claimed, TOE2 could even be applied to unearthly systems it is nowadays used to explain the dynamics of systems of cultural variations and scraps of computer code. TOE2 is similar to other theories in the special sciences, such as econometrics, ecology, and phenomenal physics it is what has grown into our modern day population genetics. Importantly, the individuals in a system governed by TOE2 need not be related by common ancestry.
TOE1 and TOE2 do, of course, interact in Darwin’s Origin. Darwin’s main aim in that work is to convince the reader that TOE1 is a better explanation for the origin of species, and their adaptations, than is special creation. The latter part of the Origin marshals evidence from embryology, geology, and the distribution of plants and animals around the globe in service of this goal. But before TOE1 can be sent into battle against the theory of special creation, Darwin first needs to convince the reader that TOE1 is a candidate explanation for adaptations and the origin of species, something that could explain these things. Darwin needs to get TOE1 on the table, and to do this, he needs a mechanism by which the adaptation and diversification of life on Earth could have occurred. TOE2 provides an account of this sort of process. Crucially, previous defenders of TOE1 lacked a good explanation of how evolutionary change could occur. So, the answer to Sober’s question, Why did Darwin write the Origin by front-loading natural selection, is that Darwin did so because he had to provide an account of how episodes of evolution leading to diversification and adaptation could occur in nature before arguing for his stance that the evidence favors his view, that life on earth repeatedly underwent such episodes of evolution, over the creationist alternative.
Darwin front-loads “natural selection” in the Origin in the sense that Darwin presents TOE2 and defends it as a theory that can explain how natural populations evolve before he considers at any depth the evidence for TOE1. But there is another sense of “natural selection” at work in Sober’s essay the transition between the two occurs when Sober writes “there is more to the Darwinian picture of natural selection than [the Malthusian argument].” Biologists are sometimes concerned with the question of whether this or that trait in this or that lineage evolved as the result of a process governed by TOE2, if you like, as the result of a process of natural selection. As Sober discusses, the features of ancestors and other relatives sometimes serve as evidence for such claims. But, as Sober notes in his discussion of Darwin’s “Malthusian argument,” “natural selection” as a general theory, what I have been calling TOE2, does not depend on common ancestry, even though facts about common ancestry are relevant to the evidence for specific claims that specific traits in specific lineages evolved by a process governed by TOE2.
In general, the evidence relevant to the question, was process A governed by theory B, is different from what makes us accept theory B as a general theory. When Sober writes that “in Darwin’s theory, and in the evolutionary biology of the present, common ancestry is not an unrelated add-on that supplements the hypothesis of natural selection,” this is true only if one means by “Darwin’s theory” TOE1, and only if one means by “natural selection” that this or that specific trait in this or that specific lineage evolved by means of a process governed by TOE2. But common ancestry is an unrelated add-on to Darwin’s theory of natural selection if one means by that phrase TOE2, so TOE2 can be presented before a discussion of common ancestry, as it is in Darwin’s celebrated work.

Elliott’s central point is that the theory that diverse living species show descent from common ancestry is not supported by evidence showing that natural selection is responsible for evolutionary change. In contrast, the theory of evolution by natural selection is supported by evidence of common ancestry. I would like to explore this asymmetry by clarifying what one means by the “theory of evolution by natural selection.”

As Elliott points out, the idea that natural selection happens, while novel in Darwin’s time, is also rather obvious. One can logically deduce that natural selection must happen given just three postulates, all elegantly explored in the Origin: heritable phenotypic variation is found in populations, some of that phenotypic variation influences the probability that organisms leave descendants, and there are finite resources. If the “theory of natural selection” is merely that selection “works,” there is no need to invoke the theory of common ancestry. After all, if there were just one population-lineage on the planet, common ancestry would not hold, yet natural selection would still be an ongoing process.

The version of the theory of natural selection that Elliott has in mind is a more ambitious one: the differences among living species, and specifically those differences that correlate with species’ ways of life, are the result of natural selection acting over long periods of time. Does this claim depend upon the principle of common ancestry? Suppose that each living species had originated independently. It would be possible that, after their origination, each species had evolved via natural selection to become better suited to their way of life? Thus, at first glance, the more ambitious theory of natural selection also seems independent of the truth of the theory of common ancestry. Somebody could theoretically hold that complex adaptations are due to natural selection even if they believed in separate origins for each living species. Common ancestry and evolution by natural selection are logically independent of one another.

Despite this independence, Elliott, is correct that the more ambitious theory of natural selection is aided by evidence that common ancestry is true and separate ancestry is false. Under separate ancestry, natural selection doesn’t do any explanatory work. Given that neither the separate nor the common ancestry models offer a theory for how life originates, there is nothing to say that life couldn’t originate perfectly adapted. Under a separate ancestry model, one theory, origination in a state of adaptive perfection, is more parsimonious (or at least no less parsimonious) than the theory that there were multiple originations in a maladaptive state, followed by selection towards greater adaptation. Under separate ancestry, evolution is superfluous. In contrast, even if the first life form was perfectly adapted, common ancestry would still requires us to explain how one ancestral form can give rise to diversely adapted, living forms. Given common ancestry some theory of adaptive evolution is needed. The question is just whether natural selection is the best theory of evolution.

Thus, I do agree with Elliott that common ancestry is supportive of the (ambitious) theory of evolution by natural selection. However, an extension of the same argument can be used to show that common ancestry also depends upon natural selection. If natural selection is the only viable theory of evolutionary change, yet selection cannot explain how one common ancestor could gave rise to descendants as different as spiders and flamingos (to give an example raised by a student this week in class), then, however compelling the evidence might support of common ancestry, we should nonetheless have to favor multiple separate origins of life. Darwin saw this clearly. He knew that evidence for common ancestry, of which he saw lots, would be undermined by an absence of a sufficient theory of adaptive evolution, as summarized in the introduction to Origin of Species:

In considering the Origin of Species, it is quite conceivable that a naturalist, reflecting on the mutual affinities of organic beings, on their embryological relations, their geographical distribution, geological succession, and other such facts, might come to the conclusion that each species had not been independently created, but had descended, like varieties, from other species. Nevertheless, such a conclusion, even if well founded, would be unsatisfactory, until it could be shown how the innumerable species inhabiting this world have been modified, so as to acquire that perfection of structure and coadaptation which most justly excites our admiration.

This quote shows that Darwin sensed that the abundant evidence suggesting common ancestry would only sway his fellow naturalists if he could open their minds to the possibility of a natural mechanism explaining adaptation. Maybe this is why Darwin wrote the origin “backwards.”

I agree with Elliott Sober that common ancestry can be tested independently of any knowledge of natural selection. In fact, I think the best evidence for common ancestry has nothing to do with natural selection and I think Darwin did too (see Chapter 13 of The Origin where he talks about classification). But this doesn’t mean that the theory of natural selection is evidentially irrelevant for common ancestry. Natural selection provides a mechanism of change which is required if there is to be any divergence from the common ancestor. It is easier to find common ancestry more plausible in the case of the pigeons in Chapter 1 than in the case of plants and animals precisely because we find it easier to imagine how populations could undergo a small amount of change as opposed to a large amount of change. This is no mere psychological bias it represents good scientific reasoning. Sober doesn’t say otherwise in his essay, but he focuses on whether natural selection is necessary for evidence of common ancestry and ignores the question of whether it can provide evidence. Providing a mechanism that can supposedly lead to arbitrarily large amounts of change as Darwin thought natural selection could (though I would debate that this is the case), makes it far more plausible that very distinct morphological groups share a common ancestry. In effect, the theory of natural selection lowers the bar for how much evidence is needed for specific arguments for common ancestry.

Another key factor that I think is missing from this discussion is that Darwin thought of his theory differently than Sober does who treats it how we generally think of evolutionary theory today. It is not an accident that the tree diagram in The Origin which is used to help explain common ancestry actually appears in the chapter introducing natural selection (Chapter 4). In the figure, the x-axis represents morphological differentiation and Darwin hypothesized that natural selection will create divergence through time through selection against intermediate states. Related arguments are given that natural selection is intimately tied to the creation of new varieties or forms and then ultimately to the creation of new species. The branching tree is a description of both process and product and therefore natural selection and common ancestry are part of a single story of the natural history of life for Darwin and not really separable hypotheses about how that story goes.

As for the real reason that Darwin put natural selection first in The Origin, I could only speculate about a number of possible reasons, none of which I would have any evidence for. But were he merely concerned with presenting a logical, structured argument worrying only about testing various parts of his theory and making sure to first argue for any premises needed for any arguments before using them, it still might be the case that he would discuss natural selection before discussing common ancestry. While it would be essential to discuss common ancestry before testing any claims about particular traits such as that mammalian skull sutures were selected for in order to ease live birth, in arguing for common ancestry, Darwin utilizes the fact that species change through time and that they multiply first by developing new varieties and then – via the principle of divergence – they develop into new species. These ideas follow from Darwin’s earlier discussions of the general theory of natural selection which do not obviously depend on prior arguments for common ancestry.

The title of Darwin’s book is On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. The title was well chosen. The hypothesis of evolutionary connections among organisms was widely discussed at the time, but the origin of the pervasive and obvious adaptations of organisms had no better explanation than divine providence. If this explanation were correct, then divine intervention must have been extremely common. And if it were so common, special creation of each species, or perhaps in some cases ancestors of small groups of species, would be only a small additional step.

Evolutionary divergence of species has two components, reproductive isolation and changes in phenotype and ecology. Virtually all current work on speciation is restricted to the first component. As a result, there is now a common view that Darwin didn’t actually explain the origin of species. This view is incorrect. What he showed is that geographic races can diverge to an indefinite extent, thereby forming what were then regarded as species. Such divergence to an indefinite extent is precisely what Wallace also explained, thereby catalyzing the writing of the Origin.

Darwin had started his notebooks specifically to deal with “the species question”. He worked on barnacles in order to gain detailed familiarity with species in a real group. The diverging characters of species commonly reflect adaptation, and explaining such adaptation was the crux of the species question.

Both Wallace and Darwin discovered natural selection by filling in a deductive argument (Van Valen, 1976). Wallace actually realized this later. This deductive argument is the only place where a Malthusian perspective enters, and both authors said that their reading Malthus led to the discovery.

Adaptation, and thereby species divergence, was the glaring hole in understanding before Wallace and Darwin. Darwin filled this hole in the first part of the Origin. He didn’t write it backwards.

Van Valen, L. 1976. Domains, deduction, the predictive method, and Darwin. Evolutionary Theory 1: 231-245.

The logical independence between common ancestry and natural selection in evolutionary theory is very interesting. The tree of life allows (and tells virtually nothing about) a number of candidate mechanisms and also – I would add – rates of change. I see such logical independence as often reflected in some “divisions of labour” in biological sciences, and in philosophy of biology as well – usually to the detriment, it seems to me, of phylogenetic issues.
Bridging common ancestry and mechanisms of change appears as a fertile ground of reflection, and I think Elliot’s idea of “evidentially relatedness” is very helpful. And, if common ancestry and natural selection need each other to shape their own evidence, who came first?
I want to argue that common ancestry came first. Natural selection was not needed for it, because another, much more ancient notion was on the table: adaptation, or adaptedness if we like.
Adaptation was deeply engrained in a philosophical worldview that saw species as perfectly designed, harmoniously adapted to each other and to their environment. As we all know, such was the view by William Paley and natural theology. Darwin had Paley’s book in his cabin on the Beagle, and Captain Fitzroy wrote in his journal, about Galàpagos finches:
All the small birds that live on these lava-covered islands have short beaks, very thick at the base, like that of a bullfinch. This appears to be one of those admirable provisions of Infinite Wisdom by which each created thing is adapted to the place for which it was intended (see this great website).
At times, appeals to the pervasive adaptive design worldview appear in the Origin, as well. Consider the following excerpt:
We see these beautiful co-adaptations most plainly in the woodpecker and missletoe and only a little less plainly in the humblest parasite which clings to the hairs of a quadruped or feathers of a bird in the structure of the beetle which dives through the water in the plumed seed which is wafted by the gentlest breeze in short, we see beautiful adaptations everywhere and in every part of the organic world (I edition, pp. 60-61).
In sum, adaptation (as a state, not a process) was something everyone could see.
In reading Darwin’s writings – not just the Origin, but also his Notebooks and The Voyage of the Beagle – I got the idea that the tree of life (or, the coral of life, but this is another story) resulted eventually as an answer to at least five puzzles Darwin had, and obstinately pursued. I wrote “eventually” although, of course, due to how mind works, it is likely that some idea of common ancestry had driven Darwin’s observations and reflections since well before his “I think” picture (Notebook B, p. 37, 1837).
The five puzzles can be seen, I think, as resulting from conflict between a growing mass of empirical observations and the assumptions of a worldview that saw species as perfectly adapted and specially created for their role and place. Such puzzles to me were:
1. Uncertainty of species boundaries due to large individual variation. To follow up from the finches example, I would point out that Darwin wrote in the Origin: «Many years ago, when comparing, and seeing others compare, the birds from the separate islands of the Galapagos Archipelago, both one with another, and with those from the American mainland, I was much struck how entirely vague and arbitrary is the distinction between species and varieties» (I ed., p. 48). Darwin was similarly puzzled by botanists, on whom he wrote: «Compare the several floras of Great Britain, of France or of the United States, drawn up by different botanists, and see what a surprising number of forms have been ranked by one botanist as good species, and by another as mere varieties» (Ibidem). How were the ubiquity of intermediates and the arbitrariness of boundaries consistent with the view of discrete, separately created species?
2. Biogeographical relationships. Darwin noticed very special similarity relations between species that are geographically contiguous. He narrated in The Voyage that, in Galàpagos, «It was most striking to be surrounded by new birds, new reptiles, new shells, new insects, new plants, and yet by innumerable trifling details of structure, and even by the tones of voice and plumage of the birds, to have the temperate plains of Patagonia, or the hot dry deserts of Northern Chile, vividly brought before my eyes» (II ed., p. 393). Why species that are created for similar environments but live far away differ more deeply than those that live nearby and are differently adapted?
3. Relationships between extant and fossil species. Here is another, purposely cryptic excerpt from Darwin’s Voyage: «The relationship, though distant, between the Macrauchenia and the Guanaco, between the Toxodon and the Capybara,—the closer relationship between the many extinct Edentata and the living sloths, ant-eaters, and armadillos […] are most interesting facts […]. This wonderful relationship in the same continent between the dead and the living, will, I do not doubt, hereafter throw more light on the appearance of organic beings on our earth, and their disappearance from it, than any other class of facts» (II ed., p. 173). Darwin was noticing that replacement in time conserves deep similarity as much as replacement in space does, and wondered how continuity in swarming variation could be consistent with special, individual acts of creation.
4. Imperfect adaptation. Darwin will extensively address this issue in his work on orchids (1877). In the Origin I would just point out a related, puzzling phenomenon: «From the extraordinary manner in which European productions have recently spread over New Zealand, and have seized on places which must have been previously occupied, we may believe, if all the animals and plants of Great Britain were set free in New Zealand, that in the course of time a multitude of British forms would become thoroughly naturalized there, and would exterminate many of the natives» (p. 337). If adaptation to local environment is perfect, how can few alien species (as we call them today) compete and supplant native ones?
5. Rudimentary organs. Darwin found the current explanation of them deeply unsatisfactory: «In works on natural history rudimentary organs are generally said to have been created “for the sake of symmetry,” or in order “to complete the scheme of nature” but this seems to me no explanation, merely a restatement of the fact […]. In reflecting on them, every one must be struck with astonishment: for the same reasoning power which tells us plainly that most parts and organs are exquisitely adapted for certain purposes, tells us with equal plainness that these rudimentary or atrophied organs, are imperfect and useless» (Origin I ed., p. 453). Yes: «Nothing can be plainer than that wings are formed for flight, yet in how many insects do we see wings so reduced in size as to be utterly incapable of flight, and not rarely lying under wing-cases, firmly soldered together!» (Ivi, p. 451). Why this?
The tree of life was an answer capable to frame all these puzzles, furthermore turning them into evidence for its own reality: intermediates were seen as transition forms, taxonomical difficulties as marks of the arbitrariness of operating cuts in a continuous process, biogeographical and temporal succession relationships as proxies for relatedness, imperfect adaptation and rudimentary organs as withstanding traces of the past.
Today we tightly link adaptation to natural selection, and undoubtedly the latter is explanatorily related to common ancestry. But the idea of adaptation has been around for thousands years, and I would say that common ancestry was established against that ancient adaptationist background. I really like Elliot’s enlightening statement:
A world in which organisms are saturated with neutral and deleterious similarities, while adaptive similarities are rare or non-existent, would be an epistemological paradise so far as the hypothesis of common ancestry is concerned.
The described paradise, however, has been far from existence in humans’ reflections on the organic world even in absence of natural selection. Another kind of paradise, one in which organisms are perfectly adapted, was the stage whose cracks triggered the discovery of common ancestry.

P.S. As for the rhetorical strategy of the Origin, I guess it could be explained by a mixture of, at least, (1) Darwin’s rewriting (and reshaping) of his research after the accumulation of evidence from multiple sources (e.g. animal and plant breeders) that he was able to do since his return in England, all concerning his mechanism for change, i.e. natural selection (2) Darwin’s attraction for mechanistic explanation, which we could see as a function of Zeitgeist, and variously define as Victorian, positivist, or informed by classical mechanics (3) the rhetorical force that Darwin could entrust, for the same reasons exposed in (2), to the mechanism of natural selection towards his audience.

In thinking about the evidential asymmetry that Elliott describes so fascinatingly, it’s helpful, I think, to recall Darwin’s fidelity to the vera causa, or “true cause”, tradition of scientific argument. I’ll briefly summarize that tradition, then suggest one way in which it seems to bear on Elliott’s analysis.

To be a vera causa thinker was to prize scientific reasoning based on causes whose existence was not merely hypothetical. Before exploiting a putative cause’s power to explain phenomena of interest, one had to show, on independent grounds, that there was impressive evidence both for the existence of the cause and for its being adequate or competent to bring about phenomena of the right magnitude. The best evidence of all was observational: the cause’s operation had been witnessed. The next best thing was inference by analogy from what had been observed.

With this tradition in view, we can, I think, be a little more discriminating about the role of evidence in Darwin’s arguments for natural selection and common ancestry in the Origin. Elliott writes: “There is an asymmetry in how common ancestry and natural selection are related to each other in Darwin’s theory. To get evidence for common ancestry, natural selection need not have caused any of the traits we now observe. But to get evidence for natural selection, Darwin needs to be able to think of present day organisms as tracing back to common ancestors.”

That last sentence is surely too quick. Yes, undoubtedly, and as Elliott brings out so well in his longer essay, part of Darwin’s case for natural selection presupposes common ancestry, as when he shows how natural selection might have brought the eye to such complicated perfection. But the relevant chapters belong, as Jonathan Hodge brought out in a classic 1977 paper, to the “adequacy” part of Darwin’s vera causa case for natural selection – that is, to the chapters showing that natural selection is powerful enough to do the causal work that Darwin wants to attribute to it.

But Darwin can address adequacy where he does only because, in earlier chapters, he has addressed the more basic question of existence. And he does that, as Elliott indicates, without presupposing common ancestry. The argument draws on an analogy with artificial selection. The Malthusian struggle for existence is an accumulating selector of variation in much the way, Darwin suggests, that the breeder on the farm is. But since the Malthusian struggle is so much more powerful, its effects will be comparably greater – resulting in new species, rather than mere varieties.

In incidental, foreshadowing ways, Darwin in these earlier chapters refers to common ancestry. But common ancestry doesn’t enter into the logic of the argument. And to that extent, the evidential asymmetry, for all its interest, looks less pronounced than Elliott makes out.

It may be helpful to distinguish two different questions here: (1) why did Darwin arrange The Origin the way he did and (2) how does Darwin recommend prioritizing appeal to common descent and natural selection with regard to accounting for evidence and explanation. As for the first of these questions, I’m inclined to agree with Grant, in that it might be usefully answered by appeal to rhetorical strategy or history. For an answer to the second, it might be more useful to look at how Darwin himself employs explanations in The Origin. Specifically, I think that chapters six and seven are especially illuminating here, as they concern responses to possible challenges to his theory.

An example of what I think Elliott is asking about can be found in Chapter 6: Difficulties on Theory, p. 187 (of the 1st edition—facsimiles of which are freely available on Google Books):

“In looking for the gradations by which an organ in any species has been perfected, we ought to look exclusively to its lineal ancestors but this is scarcely ever possible, and we are forced in each case to look to species of the same group, that is to the collateral descendants from the same original parent-form, in order to see what gradations are possible, and for the chance of some gradations having been transmitted from the earlier stages of descent, in an unaltered or little altered condition.”

This passage may present a few clues in how to answer Elliott’s query. Firstly, we might look to chapter six as an exemplar of how to consider evidence in the context of Darwin’s theory. After all, it (along with chapter seven) is dedicated to addressing possible difficulties with his theory, where he considers possibly confounding evidence (or lack thereof). This passage suggests that the best starting point for addressing many of these questions is, as Elliott suggests, common ancestry. (A point on which most contemporary systematists would surely agree!)

If one continues from the passage I cited earlier, there is a sentence that I think further supports Elliott’s general premise:

“He who will go thus far, if he find on finishing this treatise that large bodies of facts, otherwise inexplicable, can be explained by the theory of descent, ought not to hesitate to go further, and to admit that a structure even as perfect as the eye of an eagle might be formed by natural selection, although in this case he does not know any of the transitional grades.”

Notice here that priority is given to the theory of descent, as an explanation of the fact that the structure of the eye of an eagle is the product of natural selection.

So in chapters six and seven, Darwin relies on the two main features of his theory—Natural Selection and Common Descent—to answer the challenges of his imagined critic, and to demonstrate the greater utility of his theory against a design argument. And Darwin does this in a manner largely reminiscent of what Elliott describes here. But notice something else too, what are anomalies for the design argument are taken as evidence for Darwin’s theory i.e., what needs to be explained away in an ad hoc way for design theorists, is predicted and expected under Darwin’s theory. So though Elliott is exactly right when he states that:

“Rather, the point of relevance is that in Darwin’s theory, and in the evolutionary biology of the present, common ancestry is not an unrelated add-on that supplements the hypothesis of natural selection. Instead, common ancestry provides a framework within which hypotheses about natural selection can be tested.”

Perhaps Elliott does not go far enough. It is not just a question of how the two features inform evidential support for the other, what is at stake is what counts as evidence and data in biology at all.

So I largely agree with Elliott’s observations about the relation of the two aspects of Darwin’s theory and how they may provide evidential support for one another. But I think Darwin recognized this as well, and provides a model of this in his responses to the possible challenges his theory may face.

Not to go too far afield, but like Elliott, it is difficult not to consider what counts as a good mode of inference once we start down this path. Elliott asks whether parsimony ought to count as a good mode of inference, and I think that chapter six again offers us some insight into Darwin’s view on the general question of what counts as a good explanation. … Most notable here is the contrastive method (as Elliott has discussed in many places, most recently in his book Evidence and Evolution)—Darwin considers the difficulties that might be raised against his theory and considers how other possible theories might account for them. There are several things to notice about his: (1) not much stock is placed in simply being able to account for evidence within the scope of a theory. That is taken as a minimal criterion of a theory’s viability (2) In order to be convincing, a theory’s ability to account for evidence must be made in contrast to other possible theories’ accounting of that evidence.

What does this tell us about any rule of inference as a good rule of inference in biology? Contrasting two (or more) theories’ ability to account for evidence is itself a rule of evidence, and how each of these theories account for that evidence also requires some commitment to a rule of inference as being good. So in chapter 6 we get a multi-layered approach to consideration of evidential support for Darwin’s theory. I won’t delve deeper into this, but again reference back to Elliott’s work and consideration of this mode of inference in terms of likelihood analysis.

Generally I am cheering Elliott on in his discussion of how NS and CA are related in Darwin’s ORIGIN.I phrase my support like that because I do not have the specialist knowledge required to contribute to his(E’s not D’s) treatments of likelihoodist theories of evidence or post-Hennigian phylogenetics.

1.The whole question of how those late chapters of ORIGIN (X-XIII in first ed) relate to the earlier chapters cries out for clarification. A point is sometimes made as follows.In those chapters, D cites all kinds of factual generalisations —paleontological,biogeographical, embryological etc and argues that these general facts evidence his thesis of CD ( common descent ) by means of NS, because CD+ NS explains them so well , so much better than rival explanations. However, does he really show that CD+X could not be made to look just as good evidentiallyt where X is any other causation that produces gradual, adaptive, differentiationary divergence from common ancestors: Eg ‘Lamarckian’ inheritance of acquired characters.In other words does D ever show that the peculiar features of NS –the features that mark NS off from all other such candidate causes for such adaptive divergences –that those special features can uniquely get evidential support from these various facts by being the only or best candidate able do this explaining.My view is that Darwin did think he was implicitly meeting this challenge in those chapters , but I do not see him explicitly and sustainedly facing up to that challenge anywhere.I am not surpised then when some commentators read those chapters as often not engaging CA+NS at all, just CA on its own. Eliott alludes to this issue from time to timeit would be good to see a more sustained discussion.

2.On Elliott on NS as such in the ORIGIN ,I am very much in agreement , esp eg in his disagreeing with Bob Richards’ animistic Plotinian-Schellingian reading. However I do think Elliott needs to make some distinctions. He,E, tends to talk indiscriminately about ‘ evidnce for NS ‘. But that is too indidcriminate by a long way. E seems to accept a view now shared by many if not all exegeses of D’s argumatation in the ORIGINnamely that D makes three independent evidential cases for NS in this order: a case for its existence, a case for its competence to cause indefinitely, prolonged and extended branching adaptive divergences , and a case for its having been resposible for most of the divergent adaptive descent in life’s past course on earth, as evidenced by biogeography ,morhphology etc.Now, E asks whether NS is evidentially independent of CA .Well,as Greg Radick indicates in his submission, how that query is answered all depends on which of the three evidence cases we are talking about.I agree with Greg in thinking that the existence case is evidentially independent from CA, but that the adequacy or competence case is not, nor therfore the resposibilty case.

3.So much for my main suggestion about E on D on NS.Next: E on D on CA. Here I am not sure how far I differ from E.So to sharpen the issues ,let me indicate how wide the gap between us just could be.
E’s articulation of what he calls Darwin’s principle (DP) is I think way to narrow in its focus on useles traits. Sure, as he shows ,D did invoke such traits as evidence for CA.But much more often D’s argument was not about traits as such, but about similarities or other commonalities. Why do all the placental mammals have in common absence ( until man took some there) from Australia,when they can thrive there if taken by man?We can not explain this common absence as due to a common adaptation to conditions only found outside Australia and so not within that area, because just see how well they do once transported there.So a common adaptation explanation for this common absence won’t do.But a CA explanation on does nicely: the placental mammal species all descend from a CA that lived outside Australia and no descendents have been able to get to the land of kangaroo without human help.

Now notice the parallel with d on the pentadactyl forelimb structure common to bats, monkeys, whales et al. This common structure is not credibly explained as due to comm adaptation to a common way of life with common uses, because the ways of life and uses –flying ,swimming , grasping — are not common.Faced with this failure of the common adaptation explanation, what does D do? Well, he notes, we could say that the common structure is due to a common idea in the Divine mind , but D says that is not even wrong.It’s not a scientific ex at all.So what does D say? He says that CA–think of sibs abd cousins — is a known cause ( a vera causa) of similarities in oprganisms: so CA is the best explanation for these similarities between bats, monkeys and whales in their forelinb structure.So that and all such structural resemblances–inexplicable as common adaptations–among plants and animals are so many eveidential supports for CA.

Now, note,D does hold that that pentadactyl structures was first produced in the remotest ancestors as an adaptation due to NS .The structure was then an adaptation and still is, these forelimbs are still useful and are so thanks to that structure.But there is no common adaptation explanation that can be given for its being common to these diverse species–bats, whales , monkeys , becase it is no meeting the same adaptational needs and uses among them.Hence CA ( common ancestor) not CA ( common adaptation) is what they evidence. for nonadaptive resemblabces , then , invoke CA, but for the adaptive differences eg between monkey’s hand and bats wing invoke NS. So the decisive contrast is not between two sorts of traits, but between some resemblances and some differences.

If all this is pertinent then E’s account of D’s principle, does not do justice to D’s position on these issues.And that is crucial becase it was just such issues tha got D into CA originally and before he came up with NS, when indeed his package was not CA + NS, but as all close readers of the pre-NS notebooks now agree, his package was CA + Lamarck-style inheritance of acquired characters causing in the log run branching, gradual , adaptive divergenges.
(A conjecture as to why E has gone astray here:reading too much Steve Gould,onetime Leeds student, late at night.How come? SG often says history is evidenced by imperfections more than perfections ( NS is the way round perhaps).CA is about history, so CA is evidenced by imperfections.Suggestion to E: look again at D on biogeography and on morphology and, yes, the use eg of pentadactyl forelimbs in taxonomy, and see the parallels in how CA comes in for D in these places.

4.Why did D write ORIGIN as he did?We know why.( That’s academic english, of course, for I think I showed why years ago!.He did so because his very first version of what would become ORIGIN was what ? The sketch of a comprehensive zoonomical syten in the first 2 dozen pages of Notebook B , written in July 1837 months after D was a CA man but when his theory of adaptive divergence was Lamrckian and not NS because NS was still a year and a half away. And why does that sketch have the structure it does, so like the structure later given the ORIGIN?Because D knowingly gave it the the structureb Lyell gave to his exposition of Lamarck’s system ( a very different sructure from Lamark’s own.) Why did Lyell give it that structural ordering? Because h9is prime interest was in whether there are known causes for species origins in branching transmutations.He decides , no , of course. His protege,D wants to reopen the case .So, his sketch starts with known causes for species transmutations ,not with CA. So, like ORIGIN later ( and like Lyell’s’s version of Lamarck earlier) that sketch only gets to the irregularly branching tree after the case for true causes for species formations is in place.

Stand back and look at Newton’s PRINCIPA and Lyell’s PRINCIPLES and D’s ORIGIN.What structuring do thay all follow: Do the nonexplanatory evidencing for your causation first , and the the explanatory evidencing last.Ie do evidence for existence and adequacy, first , the evidencing from facts that are NOT the ones you will later use your case to explain, do this explanatory-use-independent, this nonexplanatory evidencing THEN go on to the explanatory power-use dependent evidecinhg .Darwin did as he did because Lyell and Newton had done what they had done …Herschel helped Darwin to appreciate this double precedent.So ,it’s because of N and L and H that ORIGIN was not written backwards but in the right order for a book coming after N and L.Get D’s order in the historical succession right and you’ll see why there could be only one right order for him to follow in evidencing NS without CA and then NS + CA.

I would raise three issues regarding Elliot’s Puzzle.

Elliot distinguishes two questions:

(1) Must one be able to judge whether there was selection for a trait in order to determine whether a trait shared by two species is strong evidence that they have a common ancestor?

(2) Must natural selection have been an important influence on trait evolution for there to be strong evidence for common ancestry?

He says that Darwin answers “Yes” to (1). It strikes me, then, that the answer to the question “Why did Darwin write the Origin by front-loading natural selection?” is simply that Darwin thought the answer to (1) was “Yes” — that is, he thought one must be able to judge whether there was selection for a trait in order to determine whether a trait shared by two species is strong evidence that they have a common ancestor. The real puzzle, then, seems to be why Darwin thought (if he did) the answer to (1) was “Yes.”

Two related issues arise for motivating Elliot’s Puzzle. First, in addition to (1) and (2), I would also point out that the answer to

(3) Must there be useless or deleterious similarities between species for there to be strong evidence of common ancestry?

is also “No.” Useless similarity between species is only one type of evidence presented in the Origin in favor of common ancestry. Other types of evidence play an equally important role in establishing common descent. Some of them (such as certain progressions in the fossil record) invoke adaptive modification of a lineage. Others (such as branching) do explicitly require natural selection.

Second, Elliot writes as if common ancestry is the only reasonable explanation for neutral or deleterious similarities. I agree, but there were a number of competing explanations for this phenomenon at the time the Origin was written (such as Owen’s archetype). A world saturated with neutral and deleterious similarities may be our idea of epistemological paradise so far as the hypothesis of common ancestry is concerned, but I wonder what biologists of the mid-19th century would have inferred from such a world. An important question for Elliot’s project to address, so it would seem, is whether the probability of common ancestry as an explanation for neutral or deleterious similarities was raised (relative to that of other available explanations) if one assumed natural selection as the cause of adaptation. And if so, why? As Elliot points out after the quote from the Origin, Darwin seems to have thought so.

[One thing I meant to include at the end of the penultimate paragraph]

It might be useful to think in general about how strong the case for common ancestry would have been if Darwin had made no attempt to explain adaptedness. One historical point that appears to motivate Elliot’s puzzle is the fact that common ancestry was more widely accepted after the publication of the Origin than was natural selection.

I am grateful to the commentators for their insights. In my posting , I mainly discussed the evidential relationship of common ancestry and natural selection in Darwin’s theory at the end of what I wrote, I posed a question without attempting to answer it – why did Darwin write the Origin with natural selection developed first and the big picture of common ancestry getting introduced only later? This is a question about Darwin’s rhetoric. I’ll discuss what my commentators say about this question after I address some of their other ideas.
Jon Hodge and Greg Radick both point out, as I did, that Darwin has an argument for the existence of natural selection that does not depend on common ancestry. This is his Malthusian argument. They also point out that Darwin’s argument from artificial to natural selection does not depend on the fact of common ancestry. This, of course, is correct. Notice that these two arguments leave open which traits evolved by natural selection and why they did so. It is here that Darwin uses the fact of common ancestry to think about natural selection. When I said in my posting that “to get evidence for natural selection, Darwin needs to be able to think of present day organisms as tracing back to common ancestors,” I wasn’t being careful enough.
Matt Haber emphasizes the importance of thinking about Darwin’s argument contrastively. In defending common ancestry + natural selection, what theories was Darwin arguing against? One of them was special creation. Another is a kind of “hyper-adaptationism,” according to which every organism is perfectly adapted to its environment. It is clear how biogeographical data, imperfect adaptation, and the like are evidence against the latter. It is less clear how Darwin can have evidence against the former, especially given his remarks that creationism makes no predictions about what we should observe. Darwin seems to flip back and forth between thinking that special creationism is a testable theory and thinking that it is not.
Jon Hodge asks whether Darwin ever argues that his own theory of CD+NS is better than an alternative theory CD+X. Here CD is common descent, NS is natural selection, and X is some alternative to natural selection such as the Lamarckian idea of the inheritance of acquired characters. I know of one place where Darwin does this. It is in his discussion in the Origin of the evolution of worker sterility in social insects. I discuss Darwin’s reasoning here in Chapter 2 of my book Did Darwin write the Origin backwards? The chapter is about Darwin’s views on group selection.
Jon Hodge says that Darwin has other evidence for common ancestry besides nonadaptive similarities. I don’t disagree. I didn’t intend my discussion of Darwin’s Principle to be a full account of Darwin’s picture of the evidence. In Chapter 1 of Did Darwin write the Origin backwards? I describe some exceptions to Darwin’s principle there are cases in which adaptive similarities provide strong evidence for common ancestry and other cases in which nonadaptive similarities fail to provide strong evidence for common ancestry. Hodge says that the pentadactyl forelimb is an adaptation that still is useful, but it nonetheless provides (strong?) evidence for common ancestry. I agree. Hodge also mentions a fact of biogeography – the fact that no mammals existed in Australia until human beings arrived and brought some nonhuman mammals along with them – and says that this is evidence that mammals have a common ancestor. I discuss biogeographical evidence for common ancestry in Chapter 3 of my book Evidence and Evolution. It is interesting to consider whether and why shared morphology and shared geographical location are different kinds of evidence in connection with the problem of testing common ancestry.
Chris Haufe says that one doesn’t need neutral or deleterious similarities to get evidence for common ancestry. I agree. Chris gives the example of a fossil sequence that shows adaptive modification. I discuss the evidential meaning of “intermediate fossils” in Chapter 3 of Evidence and Evolution.
So why did Darwin give natural selection top billing in the Origin? Grant Ramsey says that Darwin wanted to start with an observation that is indisputable. I agree, but it is indisputable that some organisms have common ancestors. We know this from human family trees and from the records kept by plant and animal breeders. Why didn’t Darwin start the book by building a case for common ancestry in the same vera causa style that he used to build the case for natural selection? Grant also says that common ancestry would have been a bitter pill for Darwin’s contemporaries to swallow. Grant is right what makes the pill bitter is the idea that human beings share ancestors with monkeys. We know that Darwin wanted to avoid discussing human evolution in the Origin. Maybe this was part of his reason for not starting the Origin with his big picture of common ancestry. Grant also suggests that Darwin had a stronger case for natural selection than he had for common ancestry maybe Darwin led with natural selection because this was his strongest suit. It’s hard to compare how well common ancestry and natural selection were supported by Darwin’s data, but we do know that Darwin’s audience got on board with common ancestry far more readily than they did with natural selection. Were they misreading the evidence?
Peter Gildenhuys and David Baum each point out that Darwin needs a mechanism to explain how adaptation and diversification could have arisen. I agree, but this doesn’t explain why natural selection comes first in the Origin. Leigh Van Valen notes that adaptation was the “glaring hole” in naturalistic accounts of life’s diversity – how could this be explained without divine providence? Of course, there was the influential Lamarckian idea of inheritance of acquired characteristics, at which most of us now look askance. Darwin’s contemporaries mostly did not. But even if the origin of adaptation was the gaping hole that Leigh says it is, how does this explain why selection comes before common ancestry in the Origin?
Joel Velasco says that “natural selection lowers the bar for how much evidence is needed for specific arguments for common ancestry.” Joel’s idea is that natural selection comes first because it helps Darwin make his case for common ancestry. As David Baum also notes, the incredulity that readers might experience at hearing that spiders and flamingos have a common ancestor might be lessened if a mechanism were described that can lead descendants to diverge indefinitely from their ancestors. This also bears on Chris Haufe’s question of whether common ancestry as an explanation of nonadaptive similiarites is made more plausible by natural selection’s being a cause of adaptive similarities.
Emanuele Serrelli suggests that Darwin put selection first in the Origin because he wanted to begin with the mechanism of change. Jon Hodge reminds us of the important arguments he has developed in earlier publications that Darwin followed Herschel’s codification of how Lyell and Newton argued. The goal of science is to establish the “true cause” and one begins a scientific argument by describing cases in which the existence of a putative cause has actually been observed. But what were the effects whose causes Darwin sought to identify? Hodge, like Van Valen, takes the title of Darwin’s book at its word – the mystery of mysteries is the origin of species. For them, Darwin’s problem is to identify the cause of there being different species – what gives rise to the diversity we observe? The answer to this question is natural selection. Selection causes diversity common ancestry does not. I agree that if the main goal of the Origin is to explain species diversity, or adaptation, then it makes sense to give natural selection top billing. But if Darwin’s goal is to argue for his theory – which is the theory of natural selection plus common ancestry – why should natural selection go first? Here I am reminded of an 1863 letter to Asa Gray in which Darwin wrote that “personally, of course, I care much about Natural Selection, but that seems to me utterly unimportant, compared to the question of Creation or Modification.”
Given that Darwin’s theory has two parts, and assuming that Darwin’s goal is to defend both of them, why did Darwin put natural selection ahead of common ancestry, both in the Origin, and in earlier manuscripts? The answer I develop in Chapter 1 of Did Darwin Write the Origin Backwards? is that Darwin thought that selection causes extinction and branching. The upshot of extinction and branching is the tree of life – the fact the extant organisms trace back to one or a few common ancestors. Selection comes before common ancestry in the Origin because selection has causal priority.


Why cannot there be multiple sources for same species origins? - Biology

Natural Selection: Charles Darwin & Alfred Russel Wallace

A visit to the Galapagos Islands in 1835 helped Darwin formulate his ideas on natural selection. He found several species of finch adapted to different environmental niches. The finches also differed in beak shape, food source, and how food was captured.

The genius of Darwin (left), the way in which he suddenly turned all of biology upside down in 1859 with the publication of the Origin of Species, can sometimes give the misleading impression that the theory of evolution sprang from his forehead fully formed without any precedent in scientific history. But as earlier chapters in this history have shown, the raw material for Darwin's theory had been known for decades. Geologists and paleontologists had made a compelling case that life had been on Earth for a long time, that it had changed over that time, and that many species had become extinct. At the same time, embryologists and other naturalists studying living animals in the early 1800s had discovered, sometimes unwittingly, much of the best evidence for Darwin's theory.

Pre-Darwinian ideas about evolution
It was Darwin's genius both to show how all this evidence favored the evolution of species from a common ancestor and to offer a plausible mechanism by which life might evolve. Lamarck and others had promoted evolutionary theories, but in order to explain just how life changed, they depended on speculation. Typically, they claimed that evolution was guided by some long-term trend. Lamarck, for example, thought that life strove over time to rise from simple single-celled forms to complex ones. Many German biologists conceived of life evolving according to predetermined rules, in the same way an embryo develops in the womb. But in the mid-1800s, Darwin and the British biologist Alfred Russel Wallace independently conceived of a natural, even observable, way for life to change: a process Darwin called natural selection.

The pressure of population growth
Interestingly, Darwin and Wallace found their inspiration in economics. An English parson named Thomas Malthus published a book in 1797 called Essay on the Principle of Population in which he warned his fellow Englishmen that most policies designed to help the poor were doomed because of the relentless pressure of population growth. A nation could easily double its population in a few decades, leading to famine and misery for all.

When Darwin and Wallace read Malthus, it occurred to both of them that animals and plants should also be experiencing the same population pressure. It should take very little time for the world to be knee-deep in beetles or earthworms. But the world is not overrun with them, or any other species, because they cannot reproduce to their full potential. Many die before they become adults. They are vulnerable to droughts and cold winters and other environmental assaults. And their food supply, like that of a nation, is not infinite. Individuals must compete, albeit unconsciously, for what little food there is.

The carrier pigeon (bottom left) and the Brunner pouter (bottom right) were derived from the wild rock pigeon (top).
Selection of traits
In this struggle for existence, survival and reproduction do not come down to pure chance. Darwin and Wallace both realized that if an animal has some trait that helps it to withstand the elements or to breed more successfully, it may leave more offspring behind than others. On average, the trait will become more common in the following generation, and the generation after that.

As Darwin wrestled with natural selection he spent a great deal of time with pigeon breeders, learning their methods. He found their work to be an analogy for evolution. A pigeon breeder selected individual birds to reproduce in order to produce a neck ruffle. Similarly, nature unconsciously "selects" individuals better suited to surviving their local conditions. Given enough time, Darwin and Wallace argued, natural selection might produce new types of body parts, from wings to eyes.

Darwin and Wallace develop similar theory
Darwin began formulating his theory of natural selection in the late 1830s but he went on working quietly on it for twenty years. He wanted to amass a wealth of evidence before publicly presenting his idea. During those years he corresponded briefly with Wallace (right), who was exploring the wildlife of South America and Asia. Wallace supplied Darwin with birds for his studies and decided to seek Darwin's help in publishing his own ideas on evolution. He sent Darwin his theory in 1858, which, to Darwin's shock, nearly replicated Darwin's own.


Charles Lyell and Joseph Dalton Hooker arranged for both Darwin's and Wallace's theories to be presented to a meeting of the Linnaean Society in 1858. Darwin had been working on a major book on evolution and used that to develop On the Origins of Species , which was published in 1859. Wallace, on the other hand, continued his travels and focused his study on the importance of biogeography.

The book was not only a best seller but also one of the most influential scientific books of all time. Yet it took time for its full argument to take hold. Within a few decades, most scientists accepted that evolution and the descent of species from common ancestors were real. But natural selection had a harder time finding acceptance. In the late 1800s many scientists who called themselves Darwinists actually preferred a Lamarckian explanation for the way life changed over time. It would take the discovery of genes and mutations in the twentieth century to make natural selection not just attractive as an explanation, but unavoidable.


The human skull that challenges the Out of Africa theory

This is the account of the discovery of a skull that has the potential to change what we know about human evolution, and a suppression and cover-up which followed.

In 1959, in an area called Chalkidiki in Petralona, Northern Greece, a shepherd came across a small opening to a cave, which became visible when a thick covering of snow finally melted. He gathered a group of villagers to help him clear the entrance so they could go inside and explore. They found a cave rich in stalactites and stalagmites. But they also found something surprising – a human skull embedded in the wall (later research also uncovered a huge number of fossils including pre-human species, animal hair, fossilized wood, and stone and bone tools).

The skull was given to the University of Thessaloniki in Greece by the President of the Petralona Community. The agreement was that once the research was done, a museum would be opened featuring the findings from the Petralona cave, and the skull would be returned to be displayed in the museum – something that never happened.

Dr Aris Poulianos, member of the UNESCO's IUAES (International Union of Anthropological and Ethnological Sciences), later founder of the Anthropological Association of Greece , and an expert anthropologist who was working at the University of Moscow at the time, was invited by the Prime Minister of Greece to return to Greece to take a position of a University Chair in Athens. This was due to the publication of his book, ‘The Origins of the Greeks’, which provides excellent research showing that Greek people didn’t originate from the Slavic nations but were indigenous to Greece. Upon his return to Greece, Dr Poulianos was made aware of the discovery of the skull at Petralona, and immediately started studying the Petralona cave and skull.

The ‘Petralona man’, or Archanthropus of Petralona, as it has since been called, was found to be 700,000 years old, making it the oldest human europeoid (presenting European traits) of that age ever discovered in Europe. Dr Poulianos’ research showed that the Petralona man evolved separately in Europe and was not an ancestor of a species that came out of Africa.

In 1964, independent German researchers, Breitinger and Sickenberg, tried to dismiss Dr Poulianos’ findings, arguing that the skull was only 50,000 years old and was indeed an ancestor that came from Africa. However, research published in the US in 1971 in the prestigious Archaeology magazine, backed up the findings that the skull was indeed 700,000 years old. This was based on an analysis of the cave’s stratigraphy and the sediment in which the skull was embedded. Further research in the cave discovered isolated teeth and two pre-human skeletons dating back 800,000 years, as well as other fossils of various species.

Today, most academics who have analyzed the Petralona remains say that the cranium of the Archanthropus of Petralona belongs to an archaic hominid distinguished from Homo erectus, and from both the classic Neanderthals and anatomically modern humans, but showing characterists of all those species and presenting strong European traits. A skull dating back 700,000 which is either Homo sapien or part Homo sapien is in direct conflict with the Out of Africa theory of human evolution.

Further excavations continued in the cave of Petralona with the participation of international researchers (46 specialists from 12 separate countries), which provided further proof of Dr Poulianos’ claims, including remarkable findings like fossilized pieces of wood, an oak leaf, animal hair and coprolites, which enabled accurate dating, as well as the almost continuous presence of stone and bone tools of the Archanthropus evolutionary stage, from the lower (750,000 years) to the upper (550,000 years) layers of sediment within the cave.

The research, after an interruption due to the dictatorship in Greece, continued up to 1983. It was then ordered by the government that all excavations at the site were forbidden to anyone, including the original archaeological team, and for 15 years nobody had access to the site or to the findings – no reason was provided by the government. Was this denial of access to prevent the extraction of whatever new scientific conclusions remained hidden within the incredible fossils embedded within the layers of the caves’ walls?

After the Anthropological Society of Greece took the case to the courts, 15 years later they were again allowed access to the cave. Since then the Ministry of Culture is trying in any way to overcome the Courts decision and further trials proceed.

Dr Poulianos’ findings contradicted conventional views regarding human evolution and his research was suppressed. Dr Poulianos and his wife were physically attacked and injured in their home in 2012 and the culprits were never found. He and his team have been denied further access to the cave to complete their research and study, and the whereabouts of the skull is now unknown.

Today a sign sits outside the cave of Petralona stating that the skull found in the cave was 300,000 years old, and on Wikipedia today you will see references dismissing the evidence and trying to date the Petralona skull within acceptable parameters – between 160,000 and 240,000 years old.

Recently, Professor C.G. Nicholas Mascie-Taylor of the University of Cambridge sent a letter to the Ministry of Culture in Greece saying that the correct date of the skull is 700,000 years old and not 300,000. He has also challenged the government’s suppression of information regarding this incredible discovery.

The Greek Ministry of Education, Religions, Culture and Sports,

I am writing on behalf of the European Anthropological Association, which is the umbrella professional and academic association linking all of the national European biological anthropology and human biology societies, to express our concerns about the conservation of the Petralona Cave and Skull, the misinformation of the dating of the skull, as well as the treatment of personnel associated with the conservation of the Cave.

The bases of our concerns are that the skull has been damaged through many scratches and the crown of a tooth (1st molar) cut off. As requested by Anthropological Association of Greece what is required is a detailed description of the present status of the skull, so that no one in future can arbitrarily damage it further. There is also the problem of dating which has been scientifically dated at about 700,000 years ago not 300,000 as is given at the information desk. There is a very detailed record of the excavations and findings which need to receive further public presentation but which have never been catalogued so as to prevent specimens going missing.

It is very unfortunate that the Greek Archaeological Department stopped Dr Aris Poulianos from further work in the Cave without any explanation. It is also very worrying that Dr Poulianos and his wife were physically attacked and injured in their home earlier this year and the culprits have not been found. He was also verbally abused when attempting to give an invited presentation to teachers and school children.

Senior anthropologists and geologists have also been denied access to the Cave and the specimens for further study on a number of occasions without substantive reasons. Earlier this year there has also been misinformation given to the Greek Parliament concerning financial aspects of the Cave.

I look forward to receiving answers to these questions.

Professor C G N Mascie-Taylor MA, PhD, ScD (all Cambridge), FSB, FNAS (Hungary)

Professor of Human Population Biology and Health and President of the European Anthropological Association

The most important conclusion of Dr Poulianos' research regards the co-existence of all main anthropological types (African – Kobi, Asian – Beijing and European – Petralona) at the same almost period (700,000, 500,000 and 750,000 respectively). That means: the appearance of the today human main populations (races or even better phyllae - from the Greek language and that’s why polyphyletic etc) is tending to almost 1,000,000 m.y.a. and not to only 10,000 or 30,000 years as currently considered world wide.

However, independently if there is a scientific dispute on the above, it is only sad to become aware that research is not allowed to those who are not coordinated to the “standard” knowledge, risking even their lives in front of gun shooters.

Is this a cover up of an incredible discovery that the powers-that-be do not want us to have access to? You be the judge.

Update from editor 31 December, 2018: Dr Poulianos wrote to Ancient Origins to state that unfortunately the suppression of information regarding the Petralona skull has continued: