Replies

OK, here is my reply to Why not the Neandertals? by Milford Wolpoff et al.

Wolpoff subdivides his critique of the Recent African Origin Model (Total Replacement Theory) into four sections, and so I will address each in turn.

Skeletal Anatomy

First, Wolpoff scrolls back to a 1984 article by Stringer et al. that listed nineteen characteristics of the cranial and postcranial skeleton and similar traits in their “identification of derived characters that are actually unique only to the Neandertals … provid[ing] important evidence for excluding them from the ancestry of modern humans” (1984: 54). Wolpoff then states: “twenty years later, most of these features are no longer recognized as unique to Neandertals” (2004: 529). After a few strained conclusions on that basis, he sets forth his actual criticism of Stringer and other similar analyses:

1) “The supposedly unique Neandertal features … all show considerable variation within the Neandertals and a continuous distribution from Mousterian to early Upper Paleolithic populations” (2004: 530).

2) That observations of an absence of “gradualism” in “regional continuity” (i.e., a smooth morphological transition from Neanderthal forms to post-Neanderthal forms) is an irrelevant and misguided inquiry. IOW, that the isolated or erratic appearance of Neanderthalesque features in later populations is an adequate indicium of morphological continuity (2004:530).

3) That large metric distinctions (differences in size and shape of given features) between Neanderthals and early modern humans are irrelevant, because: “Compared with other primate species, the amount of difference is just not that great” (2004: 532).

4) And, most importantly, that “numerous common Neandertal features [persisted] into the early Upper Paleolithic at high enough frequencies that a hypothesis of 50 per cent Neandertal ancestry for these European populations cannot be rejected” (2004: 532-533 – citing self).

So, in response to the first and third points, I will post the abstract of Harvati’s The Neanderthal taxonomic position: models of intra- and inter-specific craniofacial variation.

The Neanderthal taxonomic position is a matter of wide disagreement among paleoanthropologists. Some workers consider this fossil human group to represent a different species, Homo neanderthalensis, while others see it as a subspecies of Homo sapiens. This study developed two models of morphological variation to be applied to a comparison between Neanderthals and modern humans: modern human populations provided a measure of intra-specific variation, while the species and subspecies of Pan provided measures of both intra- and inter-specific morphological differences. Although such an approach has been advocated strongly, it has not been systematically undertaken until recently. The techniques of geometric morphometrics were used to collect data in the form of three-dimensional coordinates of craniofacial landmarks. The data were processed using generalized procrustes analysis, and analyzed by an array of multivariate statistical methods, including principal components analysis, canonical variates analysis and Mahalanobis D. The morphological distances between Neanderthals and modern humans, and between Neanderthals and Late Paleolithic/early anatomically modern specimens, are consistently greater than the distances among recent human populations, and greater than the distances between the two chimpanzee species. Furthermore, no strong morphological similarities were found between Neanderthals and Late Paleolithic Europeans. This study does not find evidence for Neanderthal contribution to the evolution of modern Europeans. Results are consistent with the recognition of Neanderthals as a distinct species.

Wolpoff notes this study, and simply waves his hands to dismiss it as a straw man. I find Harvati persuasive.

Then, in support of his second objection above, Wolpoff relies on the Lagar Velho alleged hybridism, that has been debunked: Hominids and hybrids: The place of Neanderthals in human evolution.

Third, and most importantly, Wolpoff ignores the Surprisingly rapid growth in Neanderthals.

Life-history traits correlate closely with dental growth, so differences in dental growth within Homo can enable us to determine how somatic development has evolved and to identify developmental shifts that warrant species-level distinctions. Dental growth can be determined from the speed of enamel formation (or extension rate). We analysed the enamel extension rate in Homo antecessor (8 teeth analysed), Homo heidelbergensis, Homo neanderthalensis and Upper Palaeolithic-Mesolithic Homo sapiens. Here we report that Upper Palaeolithic-Mesolithic H. sapiens shared an identical dental development pattern with modern humans, but that H. antecessor and H. heidelbergensis had shorter periods of dental growth. Surprisingly, Neanderthals were characterized by having the shortest period of dental growth. Because dental growth is an excellent indicator of somatic development, our results suggest that Neanderthals developed faster even than their immediate ancestor, H. heidelbergensis. Dental growth became longer and brain size increased from the Plio-Pleistocene in hominid evolution. Neanderthals, despite having a large brain, were characterized by a short period of development. This autapomorphy in growth is an evolutionary reversal, and points strongly to a specific distinction between H. sapiens and H. neanderthalensis.

I will give Wolpoff the benefit of the doubt that he was unaware of this study when he wrote his article, since the publication dates were close together, but in any case this discovery is a powerful morphological distinction between Neanderthal and Cro-Magnon; easily the most powerful morphological indicator of status as fully distinct species (excluding genetic findings).

And last but not least, with regard to Wolpoff’s alleged persistence of Neanderthal traits into post-Neanderthal populations, I will cite his own statement:

“[These traits] appear in European Neandertals at higher frequencies than other groups contemporary with them and parsimony explains them as Neandertal features” (2004: 533).

Color me unimpressed. In order to find traits whose persistence in post-Neanderthal populations signifies Neanderthal lineage then said traits must not merely appear “at higher frequencies” amongst Neanderthals, they must be characteristic of Neanderthals. Now, I recognize that Wolpoff is hamstrung by his predicate that there were no traits characteristic of Neanderthals to begin with, because they were ‘merely a far-flung branch of humans’ with constant gene flow between them and Homo sapiens, but nonetheless the four traits that he does list (533) were not unique to or characteristic of Neanderthals. They were merely traits that were not present in certain contemporary human populations, but present in others, and therefore persisted in later human populations.

Mitochondrial DNA

Wolpoff’s arguments here are straightforward. First, he simply dismisses mtDNA research that indicates the last shared ancestor of Neanderthals and living humans lived 500,000 to 600,000 years ago. His strange argument in this regard is that: “since genetic differences must always substantially antedate any population divergence” (2004:534). That’s all fine and good, but that still places the population divergence hundreds of thousands of years ago.

In any event, here’s the contrary and prevailing view:

DNA sequence of the mitochondrial hypervariable region II from the Neandertal type specimen
The DNA sequence of the second hypervariable region of the mitochondrial control region of the Neandertal type specimen, found in 1856 in central Europe, has been determined from 92 clones derived from eight overlapping amplifications performed from four independent extracts. When the reconstructed sequence is analyzed together with the previously determined DNA sequence from the first hypervariable region, the Neandertal mtDNA is found to fall outside a phylogenetic tree relating the mtDNAs of contemporary humans. The date of divergence between the mtDNAs of the Neandertal and contemporary humans is estimated to 465,000 years before the present, with confidence limits of 317,000 and 741,000 years. Taken together, the results support the concept that the Neandertal mtDNA evolved separately from that of modern humans for a substantial amount of time and lends no support to the idea that they contributed mtDNA to contemporary modern humans.

Now, Wolpoff goes on to readily concede that Neanderthal mtDNA sequences have not been found in modern Europeans, but then effectively hypothesizes that this is simply because some other mtDNA variant was selected for as being more advantageous. OK, that’s another curious argument, yet perhaps that explains it, but this nonetheless leaves us with a glaring absence of any observed Neanderthal mtDNA sequences in modern Europeans.

In short, I find the analysis that I linked above in post #10 persuasive with regard to the mtDNA issue: Modern Humans Did Not Admix with Neanderthals during Their Range Expansion into Europe. Wolpoff himself drops the posited interbreeding rate to a maximum 50% based on morphology (see quote above); mtDNA studies drop the maximum to 25%; and this range expansion model drops it to 0.1%, also on the basis of mtDNA. I find it persuasive. If others don’t, that’s OK. There’re more than enough factors to go with nonetheless, as I’ve listed (in some cases, multiple times).

Genetics and the morphology of speech

Here Wolpoff speaks to the FOXP2 gene mutation and its critical function in modern human speech and language. Wolpoff throws up a lot of irrelevant smoke and mirrors, but his basic argument resorts to this:

“Even if Neandertals or other contemporary humans lacked the modern form of the FOXP2 allele entirely, or any of the other genes that have evolved uniquely in the human lineage, no evidence suggests that the mere presence of a modern allele is a sine qua non for modern linguistic ability” (2004: 536).

In short, this is no different than the argument that “Neanderthals [may have] used different genes to perform a similar function.” That’s all fine and good, but if true, then they were using different genes, and if so, this is another powerful indicator of genetic divergence. And if they did not, this is an equally powerful indicator of genetic divergence. In short, the issue here is not whether Neanderthals could speak, as interesting as the question may be, but whether their speech capability was identical to that of humans (ergo, a shared trait signifying gene flow and genetic compatibility) or whether it was predicated upon an entirely different genotype (ergo, a divergent trait strongly suggestive of distinction).

Archaeological evidence of behavior

And finally, Wolpoff dismisses behavioral differences, that he readily concedes exist (“ranging from the absence of projectile weapons to a much smaller population size and lower population density in the Neandertals” 2004: 537) on the basis that:

“Every one of these differences can be explained by the fact that the Neandertal populations were on average earlier than Cro-Magnon ones” (2004: 537.

This is in my personal estimation a ridiculous argument. Regardless of whether “on average” Neanderthal populations were earlier than Cro-Magnon populations, said behavioral differences nonetheless are clearly attested to. Moreover, there is no evidence to my knowledge that contemporaneous Neanderthal populations erased these behavioral differences with contemporaneous Cro-Magnon populations. In other words, the differences are not merely temporal; they are uniform characteristics that distinguish Neanderthals from Cro-Magnon. So, for instance, Neanderthal did not just evidence an absence of projectile weapons in timeframes earlier than when Cro-Magnons evidence a presence of projectile weapons; rather, Neanderthals always, in all times and places, evidence an absence of projectile weapons, and this includes times and places coterminous with Cro-Magnon populations that employed projectile weapons.

For the record, the best analysis of behavioral differences that I’m aware of (and that is regularly cited in that regard) is Richard Klein’s Whither the Neanderthals? Unfortunately, I do not know of a full text link online that has general access.

So, let me know if you’d like me to speak to any of this further. This is all my personal opinion, fwiw, and others can judge my judgment as they see fit.