Thinking about human evolution never stands still. A little while ago I checked out where science was in regard to the Red Deer Cave People, an extinct species of humans who were discovered in the early 2010s. They’re intriguing – a species who manifestly aren’t us, Homo sapiens, but who seem to have been just as smart, and who lived in what is now southeastern China up until about 14,500 – 11,500 years ago.
They were, in short, our contemporaries. And they looked very different – moderate-sized brain, smaller than us with different thigh structure, and with wide and flat cheekbones. Perhaps they were inter-fertile with our species: the Neanderthals and Denisovans certainly were – we’ve found evidence of Denisovan genes both in Tibetans (where they give adaptation to high altitudes) and in the coastal populations of Papua New Guinea – who have about 6 percent Denisovan genes, in fact. We know nothing else about the Red Deer Cave people, though, other than that they ate a lot of red deer (Cervus elaphus) – hence the name – and had much the same technologies as our own ancestors. As yet, they don’t even have a defined species name. And there are a couple of things that stand out for me (other than their cheekbones).
One is that when we add this to Homo naledi (‘star man’), the Hobbits, the Denisovans and the other hominin species we’ve been finding, human evolution was obviously a lot more complex than science used to imagine. Back when I was an anthropology undergrad in the 1980s, the field was dominated by the notion of a single-species ‘advance’ from one form to another, with the exception of the Neanderthals who were (occasionally) accepted as a kind of ‘side branch’.
The problem, back then, was that there was widespread evidence of an ‘ancestral’ type – Homo erectus (‘upright man’) – which was widespread from Britain to Africa to Java. And yet we – Homo sapiens (‘wise man’) – were also evident, later, in the same places. Eugene Dubois’ notion of ancestry in Java had been discredited – we were an African species, originally – but there was no evidence of multiple exits. And so the battle-lines were drawn: either humanity had come out of Africa more than once (for which, at the time, there was no evidence) or they had – somehow – all evolved simultaneously, in different environments, in defiance of the way biology works, into a single species, Homo sapiens.
This ‘multiregional’ theory stood against known mechanisms of speciation, as advocated by Ernst Mayr and others. Normally, a species that has become geographically isolated from a cousin population will evolve somewhat differently, product of different environmental pressures and a phenomenon known as ‘genetic drift’. That’s how different species of the same base stock emerge – something observed by Charles Darwin in microcosm on the Galapagos in the late 1830s. But it’s true generally. Look at African and Indian elephants, for instance.
But in the mid-late twentieth century humans, apparently, stood outside those processes. I didn’t agree with multiregionalism at the time for this reason, though hey – back then I was just a student, which made me less than worthless in academic terms. But a lot of the main figures in the field also objected to the idea. The multiregionalists fought back with arguments about migration – populations, they insisted, surged back and forth in a kind of paleolithic love-fest that enabled genetic mixing. But it was a stretch.
So where did all that end up? Well, the whole multiregional argument foundered on evidence that emerged from the 1990s onwards, including genetic analysis. It turned out that humans had left Africa many times. The likely reason was natural climate change: humans expanded into any environment that was favourable. This changed over time, often leading to isolated populations. It also turned out that until relatively recently, in terms of the biological time spans, more than one species of human existed on Earth at any given moment – as you would expect of a genus subject to allopatric speciation and genetic drift. Each new form didn’t automatically replace the last at all. Some vanished as their environments changed. But others did not. Furthermore, not only was our own species, Homo sapiens, just one of several species of human; but contrary to the old notion of ‘advance’ mediated on brain size and hence intellect, many of our cousins had brains within our own size-range, and similar technologies.
Indeed, two of our closest cousins had bigger brains than we did. In a way that is perhaps neither here nor there. On the basis of the ‘Hobbits’, who had chimp-sized brains but also used tools, fire and probably spoke, it appears size is less an arbiter than internal organisation. But, if recent discoveries are correct, our two bigger-brained hominin cousins also had better stone-age era tech than ours. And yet only we – Homo sapiens – survived. Furthermore, genetic analysis shows that our species, who represents all humans alive today, is genetically so close that, if we were dogs, we’d be the same breed. This is unusual and means we, too, suffered a very tight population bottleneck.
In other words, science has shown that there is no material difference between any of us alive today; and our wider genus – humans – basically went extinct during the harshest part of the last ice age. Our own species missed the climatic death-blow only by a whisker, and likely by chance. That makes us the last humans. All of us. Together. And what have we done with that responsibility? Um…
Copyright © Matthew Wright 2017