Re-thinking human evolution… again

I have been fascinated of late with the way our understanding of human evolution has forged ahead in leaps and bounds.

This year alone we’ve discovered that Homo naledi, the previously unknown ‘archaic’ species that was discovered in a South African cave, was still going just 250,000 years ago and – very likely – had the ability to speak. We’ve also found evidence that the ‘Hobbits’ of Flores Island aren’t a diminutive of ‘Java Man’, Homo erectus, but likely descended from a different branch of the human family tree. And there’s the discovery that our own species, Homo sapiens, likely dates back at least 250,000 years.

What all this adds up to is that the old idea of progressive one-thread evolution from ape to man, in which each type was wholly replaced by the next, is right out the window.

Human evolution as ‘progress’, public domain, via Wikipedia.

Mind you, that idea was pretty dodgy even when Ernst Mayr and others were popularising it in the mid-twentieth century. Looking back, that ‘march of progress’ rested on the supposition that humans – alone – apparently weren’t subject to speciation like everything else. Our ‘evolution’ instead consisted of a steady ‘progression’ of types, an ‘advance’ apparently defined by male silhouettes revealing the relentless expansion of a single body part (no, not that one…)

A lot of that thinking was founded in nineteenth century concepts of progressivism and could be applied without much problem when hard evidence of human evolution was contained in literally a few dozen fossils. Current humanity was also a single species, and it was easy to assume that this had always been the case. The fact that Homo sapiens are the sole surviving species of a wider family that once had the same style of speciation as other animals wasn’t visible. Now it is – down to the point where, in yet another rather cool break-through, it’s been found possible to sift cave dirt and discover hominin DNA within it.

What it adds up to is a very different picture of human evolution from the twentieth century certainties. Both the old-style ‘out of Africa once’ hypothesis and its competitor, ‘multiregionalism’ – in which humans in widely dispersed environments around the world somehow all evolved to become exactly the same species at exactly the same moment – are dead as dodos.

Today’s understanding is very different.  Sure, we’re all one species today – indeed, genetically we’re unusually close by normal measures. But that’s because we are the sole survivors of the wider human family. Like every other species, humanity was subject to speciation. Our human family also left Africa many times, spreading around the world and further diversifying.

Holotype specimen of H. naledi, Berger et al, Creative Commons 4.0 license via Wikimedia.

There is also good evidence that the differences of capability between most of these human species were of style rather than of degree. After a certain point, different human types weren’t lesser than us – just different, like lions are different from tigers. But what our relatives did was still recognisably human.

We know this because, in another whittling away of discredited twentieth century thought, all of the features we foolishly regarded as unique to Homo sapiens alone – creativity, art, speech and technology – have been shown to be shared with our fellow human types. Neanderthals, it seems, weren’t thuggish brutes who spoke in grunts. They made jewellery, played musical instruments using the same tonalities as ours, and developed epoxy resins from birch bark, which they used to glue spear-heads to hafts. They then used those spears to ram large beasts and wrestle them to the ground. Neanderthals were twice as a strong as we are, you see, and at least as smart. Their brains were actually bigger than ours. Or take Heidelberg Man, Homo heidelbergensis, who on average was a little taller than we are and had a brain size within our own average range. They flourished from North Africa to Europe half a million years ago. Were they cave men? No. The remains of their houses, built from reeds and local materials, have been found in southern Spain.

All of them, it seems, were humans – and to a large part human by our own definition, including having speech. They didn’t do things quite the way we did, but why would they? They weren’t us. But they seem to have been just as a smart, just as capable, and just as creative in their own way.

What’s changed is our view of how evolution works and how living species are inter-related. It’s not a nineteenth century progressive-style ‘tree’ in which ‘higher’ means ‘more advanced’ and lower ‘more primitive’. It’s better to present it as a kind of wheel in which species are portrayed around the perimeter, including surviving ancient species – they’re not ‘primitive’, so much as ‘they didn’t need to change’. Here’s what it looks like – click to go through to the original site which offers a printable download covering 3000 species (and how cool is that!):

Tree of life, 21st century style – click to go to a high-res download with 3000 species named

So the modern picture is that, instead of us being at the ‘top’ of the evolutionary ‘tree’, we’re just a part of the general mix. And there probably wasn’t such a lot of difference between us and our cousins. I’ve actually seen it argued that all human species are merely variations on H. erectus/ergaster, who first emerged in the early Pliestocene about 1.9 million years ago. By this argument (which runs against Mayr’s species definition mechanism), all human species should really be classified as sub-species of Erectus/Ergaster, who used fire, made tools, and flourished variously from Java to Britain to Russia to Africa over a period of at least 1,500,000 years. Or maybe longer depending on which date you accept for their extinction.

Either way, the fact remains that of all the different human species alive even 50,000 years ago, only ours remains. Even our closest relatives – the Neanderthals and Denisovans – are gone. And the evidence is growing that we survived not because of some innate smartness or some advantage we alone had, but purely by accident. We came pretty close to going out, too, around 70,000 years ago.

Intelligence, it seems, is not a survival advantage – not ape intelligence, anyway. All it leads to is in-fighting and resource destruction. But we survived anyway. And now we are the last humans.

It is a weighty responsibility. Let’s not blow it.

Copyright © Matthew Wright 2017

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7 thoughts on “Re-thinking human evolution… again

  1. Reblogged this on Wind Eggs and commented:
    Disturbing to some, heresy to others, our thinking on evolution has evolved. (I would like to say “evolved again” but that would be redundant.) If you understand evolution this should come as no surprise, but it may be time to rethink how we treat the other species on this planet. In the meantime, Matthew Wright, shares an update.

  2. Brilliant post Matthew, I was recently reading about the new discoveries which indicate the human story is much more complex and indeed older than science previously thought. You gave am elegantly summary that focused my thoughts on this tortuous field wracked with uncertainty and contradiction. Thanks

  3. Thanks for summarizing this so well, and the reminder that we are the last humans. Of course, if we sputter out, the earth and its remaining life forms will go on, without stopping to weep for us. Fascinating image, too!

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