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our ancestors and their climates

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In a number of posts here I’ve been scratching around in the field of human origins, getting lost among the taxonomic shrubbery, and getting vaguely annoyed, and vaguely suspicious, about the endless claims over new species, often from the merest fragments of remains. Though I’m pretty ignorant about it all, my sense is that not enough allowance is given for variation, and that there are more connections between particular finds than are acknowledged.

Being still a bit old school, I often prefer to read about this stuff in books and magazines than on science blogs or podcasts, so a wee foraging trip to the local bibliotheque has uncovered a 2010 book by Clive Finlayson, The humans who went extinct: why neanderthals died out and we survived, which has provided me with the best general education on human origins of anything I’ve read so far. In this post I’ll focus on the first two chapters of the book, so I’ll barely be touching on neanderthals. I’ll be looking at the landscape and environment of the proto-humans in all their variety.

Finlayson is an evolutionary ecologist, so landscape and environment [which combined together make for habitat] is his bag. He’s particularly interested in and knowledgable about how climate changes have created and destroyed habitats and their populations over time.

We often associate the success of mammals with the chance extinction of the dinosaurs at the K/T event, 65 million years ago, but in fact they were quite prevalent before this, as recent fossil evidence has shown [the earliest mammals so far found being dated to 170 mya]. The massive K/T event destroyed all living creatures larger than an average dog, including all dinosaurs and probably most mammals. The first primates that we have evidence of appeared after K/T, about 60 mya. However, a decisive global warming event at the boundary between the Palaeocene and the Eocene [55mya] proved a boon for these early tree-dwelling primates. In a short space of geological time, surface temperatures warmed to such an extent that evergreen forests stretched into high latitudes of the northern hemisphere, and primates spread  north-east from southern Asia into North America, heading south and further east into Europe, the land being connected in ways hard to imagine now. The fossil record fully bears out this great north-eastern expansion.

Finlayson makes a very important and useful distinction between expansion and migration here, which is particularly important when we consider the spread of Homo sapiens much later. He illustrated this with the tale of the collared dove, a species which made its first observed European appearance in Turkey in 1900. By the 1960s it was becoming prevalent in Britain, having, in the interim, expanded its collective territory in an east-westerly direction, with an estimated European population of approximately seven million breeding pairs currently. So they encountered a congenial habitat throughout Europe, going forth and multiplying and expanding their range. No migration necessary – a bit like bacteria expanding in a petri jar full of nutrients. This is the way Finlayson sees populations of proto-ancestors expanding and contracting as environments changed from thick, lightless forest to sparse woodland and savannah as regions cooled, and vice versa. Some populations were better adapted to one type of habitat than another, and they died out with rapid climatic change, or were reduced to scattered remnants. He also makes an interesting distinction between innovators and conservatives among these populations. The innovators were for the most part living on the edges, at the ever-changing boundaries between habitats, inventing because of necessity as change occurred more rapidly there and flexibility was paramount. The conservatives gravitated to the centre of habitats, moving with them as they shifted southwards or northwards, consolidating their narrow range of skills in times of stability, but often dying out when those habitats finally vanished. All of this applied to mammals other than humans too of course, and none of it involved conscious decisions, and there was a great deal of luck involved, what with greater and lesser ice ages and other extreme weather or geological events, such as the Toba volcanic explosion of more than 70,000 years ago, the likely cause of a bottleneck in our ancestral population. There were also pockets of habitat, microclimates if you will, which underwent such rapid, up and down changes in temperature and ecology that they could be measured in generations rather than millenia, and they may well have encouraged rapid adaptation. The story is complex and multi-faceted, and I’m already beginning to see how this might have impacted on the neanderthals, who were unlikely to have been ‘wiped out’ by other humans as has sometimes been suggested. Climate appears to have got them in the end, as with so many other species. The last neanderthal population known about was confined to the south-western Iberian peninsula. It’s likely that the last neanderthal eked out his or her lonely existence in a cave now known as Gorham’s cave on Gibralter, some 30,000 years ago. However, archaeology never stops surprising us, as this report shows.

It raises the question of whether Mousterian technology must always go hand in hand with neanderthal populations, and Aurignacian technology with our ancestors [I hope to look at these and other ancestral technologies in another post] . Finlayson describes this belief as ‘a symptom of a long-standing, and in my view, highly erroneous, observation among some archaeologists that equates biological entities, such as the neanderthals, with particular cultural traditions.’ This is no doubt a debate that has a way to run yet.

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Written by stewart henderson

November 27, 2011 at 5:22 pm

Posted in Uncategorized

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