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more on human ancestry

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Homo erectus

This is a fantastic time to be interested in human origins.

[Ed Yong, ‘Not Exactly Rocket Science’]

The post linked to above, and probably plenty of others I could’ve linked to, makes my previous post on human origins look decidedly amateurish. But after all, I’m an amateur. And that’s all good, I’m just trying to educate myself here.

The Yong post doesn’t concern itself with how far back we can trace our distinctly human ancestry, but it does refer to the multi-regional model of origins, which I carelessly mentioned in my post, and it focuses on the latest analyses of our relations with Neanderthals, through computer simulations of the spread of populations and examination of the Neanderthal genome. It also mentions a recently discovered type of archaic human called the Denisovans, with whom we also interbred. This sounds confusing, as you might think we  were archaic humans when we bred with them, but apparently not – or perhaps not quite so archaic as Denisovans.

It seems from my reading that ‘archaic’ here means a form that’s no longer extant, rather than a form that’s less developed or more ‘primitive’. Evidence of the Denisovans comes from a finger bone found in Denisova cave in Siberia, only in March 2010. Mitochondrial DNA from this hominin bone, which dated back 41,000 years, suggested that it was distinct from both Neanderthals and modern humans. Next, a team examined and sequenced the nuclear genome of this hominin [all from a wee finger bone], aided by the fact that DNA is better preserved in cold climates. As we know, the Neanderthal genome and the modern human genome have also been sequenced, and a comparison of results has shown that the Denisovans and the Neanderthals shared a divergent branch from the line leading to modern African humans. The branch diverged from the lineage some 800,000 years ago, with Denisovans and Neanderthals diverging from each other some 640,000 years ago.

That so much can now be gleaned from such scant fossil finds does tend to excite. Only last year another early species of Homo was identified, H gautengensis, through analysis of a specimen found back in the seventies in the Strekfontein caves of South Africa. This species is believed to predate H habilis, emerging more than two million years ago and dying out about 600,000 years ago. It was big-toothed and small-brained, little more than three feet tall, and weighing around 50kgs. It was bipedal on the ground but probably spent most of its time in trees, and it lived largely if not entirely on vegetable matter. Can we identify such a creature as human? It probably lacked speech or any language capacity. We can’t analyse its DNA, but anatomical and other research suggests it is a close relative of H sapiens, if not a direct ancestor.

These recent discoveries of possibly or probably new lineages are due to a convergence of new techniques and accumulated knowledge – we know better where to look and what to look for. More discoveries await analysis, and previous finds await reappraisal. It looks as if our Homo ancestry will get a lot bushier as a result. There’s a bit of a language issue here. Homo sapiens are clearly human beings, and they’re direct descendants of another Homo species. H erectus is the most likely candidate, but we’re far from sure. In any case, at the point of divergence there would’ve been little noticeable difference between our species and its immediate ancestor. This difficulty about beginnings is compounded by our naming the whole genus Homo, Latin for ‘man’, in the gender-neutral sense. The genus is more than 2 million years old, our species may only be about 200,000 years old. Many would argue that H gautengensis, given the description given above, is not human. Others would argue that it is, or at least that it is proto-human [though this is problematic as it suggests a human ‘prototype’, a rather teleological term]. So the original question, how long have humans been around is dependent both on how we define ‘human’, and on what we can properly infer from the data. For example, though we might be able to infer much about the lifestyle of H gautengensis [I don’t know how they managed to work out its probable diet] from modern analyses, we might never be able to know how we’d have reacted if we’d met a specimen. Would we see recognition in its eyes? Could we have befriended it [or him, or her]? How would we have communicated? It’s more likely, of course, that both groups would’ve exhibited in-group/out-group hostility, but even so, it’s hard to imagine what that hostility would’ve felt like, with its admixture of recognition, curiosity and wonder.

In any case, for those who might want to argue that  the species H sapiens and H sapiens alone is truly human, there are more complications. In 1997 remains were found in Ethiopia of a probable subspecies of H sapiens, since named H sapiens idaltu, dating back 160,000 years. The remains consisted of three craniums, and who knows how many other remains are yet to be found, of this and other subspecies. So now we prefer to call ourselves H sapiens sapiens, but more of that another time.


Written by stewart henderson

September 15, 2011 at 9:53 pm

Posted in anthropology

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  1. […] been writing a bit about the origins of Homo sapiens, for example here and here, but I’ve said virtually nothing about Australopithecus sediba,  a species, sub-species or […]

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