[LINK] "The end of archaic h. sapiens"

[rfmcdonald]

Razib Khan's post at Discover's GNXP taking a look at the origins of Homo sapiens. This is a surprisingly complicated question, especially now that it's well-known Homo sapiens sapiens includes representatives from at least two highly distinctive hominid populations, the Neandertals and the recently-found Denisova.

One of the terms in paleoanthropology which can confuse is that of archaic Homo sapiens (AHS). This is in contrast to anatomically modern humans (AMH). A simple Out of Africa “recent-origin-with-replacement” model allowed to sidestep the semantic imprecision in tossing disparate populations into a generic category such as AHS (similarly, the term “animal” as opposed to “human” has some colloquial utility, but it’s not scientifically useful). But the possibility of admixture from archaic lineages in modern human populations forces us to grapple with the dichotomy between AHS and AMH, as modern humans may be a compound of these two categories (not to mention the idea of behaviorally modern humans, who are a subset of AMH).

I assume that fleshing out the details of a new paradigm which is both precise and accurate will be a project for the coming years. But before we move on we need to fix more sturdily our understanding of the genealogical relationships of contemporary human populations. Over the past few years there have been major strides in this domain, confirming the broad outline of a dominant African heritage for modern humans. Geneticists have moved from classical markers to SNP data, focusing on hundreds of thousands of genetic variants. But now they’re shifting to whole genome sequences, which with errors excepted encapsulate the totality of the lowest order aspect of human genetic variation.

Razib takes a look at the paper. The conclusion? The hunter-gathering San of southern Africa are the most distinctive populations because of their very early separation from the other human populations of the world, even other Africans.

Notably, our point estimate of ~130 kya suggests that the San divergence occurred ~2.5 times as long ago as the African-Eurasian divergence, that major human population groups diverged at least ~80,000 years before the out-of-Africa migration and that the San divergence is more than one-third as ancient as the human-Neanderthal divergence…Still, human effective population sizes are sufficiently large that these divergence times are small relative to the time required for lineages to find common ancestors in ancestral populations. Indeed, of the mutations differentiating a San individual from a Eurasian individual, only about 25% are expected to have arisen since the San divergence. Thus, the ancient divergence of the San population does not alter the essential fact that far more human variation occurs within population groups than between them.

Razib continues, noting that the San/non-San and Neanderthal/AMH divergence is a matter of degree, not type.

There’s now a fair amount of data and results which indicate a deep divergence between the traditionally hunter-gatherer populations of Sub-Saharan Africa and the farmers and agro-pastoralists of the continent. If these results are correct (and they seem to be in line with the earlier genomic analysis of the Bantu and Khoisan from South Africa) then we have here a rather straightforward refutation of the very simple Out of Africa model, where one East African group replaces everyone else. The Bushmen seem to be of another lineage. Secondly, these results suggest that we should be cautious about inferring a qualitative difference between Neandertals and AMH, where the former is bracketed as “archaic”. The difference between Bushmen and non-Bushmen is far less than between Neandertal and AMH, but it is by a factor of multiples, not order of magnitude.

Fascinating. What will come next out of the labs of the geneticists and the sites of the physical anthropologists and who knows what else?