Rethinking human evolution – again

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).

Artists’ reconstruction of H. georgicus, a variant of H. erectus which was likely the original human form – arguably every species since has merely been a variation on this incredibly successful hominin.

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…

More soon.

Copyright © Matthew Wright 2017

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13 thoughts on “Rethinking human evolution – again

    1. Certainly have, and it’ll get worse before it gets better. If it gets better… I think the way we exploit every environment to the point of destroying it, all the while viciously fighting anybody defined as ‘not our kin group’ (now intellectualised into other forms), is a misfired survival tactic from our ancestral period – worked a treat when there were a few thousand of us in Africa. When there’s 7.5 billion? Not so much.

      1. Precisely why we need to either: become extinct before we make the planet completely derelict, or, reduce our numbers dramatically and rapidly – leaving enough technology and skilled folks to rebuild after lessons have been learned – hopefully…

        1. Exactly – and we also need to change the way we behave towards each other. It’s always a case of ‘us’ versus ‘them’, where some other group is defined as ‘them’, and we are very skilled at destroying them, either figuratively (as happens here in NZ in intellectual circles) or literally. Mix that with our ability to destroy every environment and… yah. Moving to another planet (as Hawking and others suggest) won’t work. Technically we could do it, if we had the motivation, but it wouldn’t change the behaviours that led to Earth being environmentally wrecked while we fought over what was left. Ugh…

  1. I’m gobsmacked. I’ve read a little bit about human evolution – e.g. The Hobbits – but I had no idea about any of this. So…you’re saying that we were a remnant of humans that just happened to survive some catastrophe and then spread to fill all the vacant niches?
    I’m not at all religious but that bears a rather chilling similarity to the story of Noah and the Deluge. Or at least to the idea of a small band of /survivors/ restarting the world.
    Sadly you’re right about the mess we’ve made of it.

    1. It’s not my theory but that of those working in the field. I did an undergrad degree in anthro but haven’t since pursued it actively, though I keep up with the science of it because it’s so fascinating – and has totally been turned over by new discoveries. Yes, it would seem that we are the only human species that didn’t go extinct, and we had cousins around until, in geological terms, an eye-blink ago. The problem likely wasn’t a single catastrophe but a general environmental downturn such as the advent of a period of glaciation which affected the planet – there is speculation that the Neanderthals were finally wiped out by a new ice age that began about 26,000 years ago and may have been triggered globally by a colossal eruption of the Taupo volcano in New Zealand. The fact that several species such as the Red Deer Cave people seem to have vanished with the onset of the Younger Dryas (about 12,900 BP), possibly on the back of a cometary impact (speculatively) is interesting. More data is needed. And when it comes, we’ll doubtless revise the whole picture again.

  2. Very interesting article Matthew. We are apparently overdue a ‘mass extinction event’ by some millions of years. Scientists have long speculated that there have been many of these. With the population now out of control (7.442 billion as of 2016), great stress has been put on the climate, and plastics in the oceans have recently been highlighted as a real issue that we seemingly have no solution for.

    German archaeologists from the Museum of Natural History in Mainz, have recently discovered a 9.7-million-year-old set of teeth, discovered from the riverbed of the Rhine that don’t appear to belong to any species discovered in Europe or Asia. They most closely resemble those belonging to the early hominin skeletons of Lucy (Australopithecus afarensis) and Ardi (Ardipithecus ramidus), famously discovered in Ethiopia.

    But these new teeth, found in the western German town of Eppelsheim near Mainz, are at least 4 million years older than the African skeletons, which has scientists so puzzled they held off publishing for a year. In the press conference announcing the find, Mainz Mayor Michael Ebling claimed the find would force scientists to reconsider the history of early mankind – in that we didn’t come out of Africa after all.

    The teeth are still being examined in detail, after which they will go on display at the University museum in Mainz. http://www.dw.com/en/archaeology-fossil-teeth-discovery-in-germany-could-re-write-human-history/a-41028029

    1. This discovery is fascinating and adds to the jigsaw of evidence science has about human ancestry and spread. It’s possible that the Australopithecines were more widespread than envisaged originally (they’ve been postulated as direct ancestors of the Hobbits, for instance). What strikes me is that although we often view our geographical origins in terms of the continents, the reality back then was that all species of human, ape etc inevitably followed patterns of habitable territory. These usually spanned continents, so it’s possible that the Australopiths were able to make their way into Europe that way. The huge variety of ape and early human species found in Africa, by comparison with elsewhere, suggests that we are an African ape, originally, but one that perhaps spread quite widely. We’ll find out, I’m sure – science is all about revising theories when new evidence comes along. I guess it’s a matter of ‘watch this space’.

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