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Open Access Highly Accessed Question and Answer

Q&A: Who is H. sapiens really, and how do we know?

Mason Liang and Rasmus Nielsen

BMC Biology 2011, 9:20  doi:10.1186/1741-7007-9-20

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Fig. 1 as seen from the Americas

German Dziebel   (2011-06-10 16:20)  Great Russian Encyclopedia

This is all fine and dandy. And very well-written. Let me try and throw an anthropological "tomahawk" into the existing models of human origins.

If we compare Fig. 1 with all its previous iterations, we notice the emergence of Melanesians as a distinct population within non-Africans. This amendment reflects the recently established Denisovan-Melanesian genetic match, which made Melanesians qualify for a special place among the great divisions of humanity. Amerindians, on the other hand, are still "missing in action" on these charts. Why? X chromosome B006 haplotype, which has a Neandertal match, is found at highest frequencies in Amerindians, of all continental groups, and at lowest frequencies in Africans. Blood group O, which is most frequent in Amerindians, again showed an intriguing match in the 2 Neandertal individuals tested for classical markers. Paleoindian skulls don't have a "Mongoloid" or a "Caucasoid" morphology suggesting that Amerindians had split off from other humans before the formation of these two continental groups. Then how come Amerindians are not on the chart? Or, let's take levels of linguistic diversity. Amerindians are divided into 140 language stocks, which constitutes 2/3 of world linguistic diversity. Africans have only 20. This suggests that the New World, just like Melanesia, has a long history of fragmented demography, which maybe is hard to capture archaeologically but which harkens back to Mid-Pleistocene population realities. The fact that language - one of the key diagnostics of behavioral modernity - shows low variability in Africa and high variability outside of Africa - connects nicely to the fact that the so-called African "anatomically modern humans" are poorly associated with signs of behavioral modernity. Behavioral modernity firmly appears in the archaeological record in Africa (and elsewhere) only some 40-50,000 years ago. How can we assume that "anatomically modern humans" are "our" ancestors if in all living modern humans modern anatomy is inextricably tied to modern behavior?

Let's also ask ourselves: How far is 50,000 YBP from the known horizon of modern human occupation in the New World? The recent discovery of the Zhirendong chin in South China that instantly pushed the dates for modern human presence in Asia back by 60,000 years suggests that the temporal gap is not that dramatic.

The recent discovery of a proto-Clovis toolkit in Buttermilk Creek, Texas (instead of expected NE Asia or Alaska) pushed the known time of New World occupancy to 16,000 YBP. More importantly, it suggested that we just don't have enough hard data to argue for a recent peopling of the Americas. There's no string of archaeologically identifiable and Siberian-looking cultures connecting NE Asia through Alaska with Texas in pre-Clovis times. Sky is the limit there in terms of the potential time of entry into the New World. It's possible that the antiquity of human presence in the Americas manifests itself not in lithics but in languages.

Amerindians, therefore, shouldn't be brushed aside as a recent population irrelevant to the question of the origins of modern humans. In "The Genius of Kinship: The Phenomenon of Kinship and the Global Diversity of Kinship Terminologies" (2007) I introduced the idea that, if we take all the interdisciplinary data into account, we can't exclude the possibility that modern humans 1) evolved not from African archaic hominids but from East Asian archaics; 2) speciated into "us" not somewhere in Africa - already populated by archaics - but in a region previously unoccupied by hominids, namely in the New World; and 3) finally, expanded out of their homeland not through the territories thickly occupied by Neandertals (Neandertals did replace "anatomically modern humans" in Southwest Asia, didn't they?) but through the lands sparsely populated by competing hominids. After a bottleneck associated with the speciation event in such a marginal area as America, modern humans migrated back into the Old World, expanded in size, intermixed with each other and replaced hominids on all continents. This model explains the behavioral uniqueness of modern humans better than the other ones. Fig. 1 could, it would seem, be complemented by a third, out of America, model, the paleobiological and archaeological support for which may be up for recovery in the future, while linguistic and ethnological support has been in abundance for a long time.

The traces of "archaic admixture" outside of Africa may, in fact, be traces of common descent from non-African hominids. These genetic findings bring back some of the arguments for regional continuity in Asia that involved such palpable morphological features as shovel-shaped incisors (frequent in Asians, Amerindians and Neandertals) and facial flatness, among others. The divergent position of Africans among modern human populations may be the result of homoplasies with chimp sequences. It seems odd that hominin genomes "waited around" for several million years until modern humans migrated out of Africa to develop mutations from orthologous chimp sequences. We are still missing ancient DNA from "anatomically modern humans" in Africa or from African archaics to ascertain if modern African divergence is indeed that old. Alternatively, African divergence may reflect a greater degree of modern human admixture with African archaics in Africa than with Eurasian archaics in Eurasia. If the degree of divergence reflects the depth of admixture, then the "purest" humans would be found on a continent that has no history of occupation by hominids, namely, again, in the New World.

To sum up, Fig. 1 has evolved considerably over the past 10 years, but it still looks like a medieval map on which the New World is missing because unknown yet.

Competing interests

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