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August 17, 2012 8:58 pm
Evolving: The Human Effect and Why it Matters, by Daniel J Fairbanks, Prometheus Books, RRP£16.99/$19, 352 pages
Masters of the Planet: The Search for Our Human Origins, by Ian Tattersall, Palgrave Macmillan, RRP£16.99/$26, 288 pages
Homo Mysterious: Evolutionary Puzzles of Human Nature, by David P Barash, OUP, RRP£18.99/$27.95, 384 pages
Once upon a time, there was an ape that stood up. Why it stood up nobody knows, but once upright it found it could use its hands to fashion tools from sticks and stones. So it stayed standing up. And once it decided to stay standing up, its brain started to grow. Why its brain started to grow nobody knows, but with a bigger brain the ape, which was by now an ape-man, could make better tools and even speak. Why it started to speak nobody knows. And by then it wasn’t an ape-man any more, but a human. And those humans with the most developed brains – Homo sapiens – used their cunning to spread throughout the world. All the many other kinds of human and ape-man died. Why they died nobody knows.
When the Homo sapiens were lords of all, some of them became curious about where they had come from. Having a poor collective memory, they at first thought the world had simply been handed to them by a god who happened to look just like they did. But a few began using their inflated brains to try to piece together a story about how it had all begun with an ape that had once stood up. And three of them even wrote new books on the subject.
There remains something about the evolutionary account of our origins that sounds a little like a just-so story. Until a century and a half ago it would have been regarded by the most educated person as just that – a witty tale in slightly poor taste; science fiction perhaps, but not science. This incredulity lingers: although now firmly established in the minds of most Europeans, evolutionary theory remains highly contentious worldwide. Notoriously, this includes in the US. According to a Gallup poll conducted this year, nearly half of Americans believe we humans were created by God just as we are today, whereas a further third believe in a process of “intelligent design” guided by a divine hand. Only 15 per cent accept that we evolved unaided from some surprisingly upright apes.
This reflects a kind of paradox: although our brains have ballooned over the past million years or so, we still struggle to understand ourselves. Nowhere is this more obvious than in the study of our origins. That we evolved is considered by the scientific community to be established beyond reasonable doubt, yet at the same time there remain enormous gaps in our knowledge of how it happened. Some of the most fundamental details of our development – why our ancestors became bipedal, or why their brains tripled in size – remain unexplained. In different ways, all three of the books under consideration here wrestle with this problem. Taken together, they give a good overview of what we really know about our primate past and what we don’t.
The gaps in our knowledge make life uncomfortable for those who are struggling to defend evolutionary theory against the dogma of creationism. The biologist Daniel Fairbanks helps to run workshops on evolution for embattled American high school science teachers and is therefore well aware of the “ongoing criticism, even threats” to which they are subjected. In his book Evolving: The Human Effect and Why It Matters he therefore aims to spell out why we can be so sure that our ancestors were apes.
Fairbanks begins his useful and accessible survey with the evidence written into our bodies – the peculiarities that no intelligent designer would ever have designed. By comparison with our ancestors, for example, we have small jaws, yet we have the same number of teeth – with the consequence that we suffer from tooth crowding, as anyone who has had to have their wisdom teeth removed will know. This would be an odd thing for a deity to intentionally construct. It is rather a vestige of our evolutionary past, like the useless hind leg bones found deep inside whales.
Fairbanks, however, devotes most space to the newest, yet perhaps most important, source of evidence for our evolution: the story told by our genomes. If the theory of our evolutionary origins were true, we would expect species that split off from each other recently to have similar genes. And this is exactly what we find: we share 98 per cent of our DNA with our nearest living relative, the chimpanzee. This applies not only to the DNA that actually makes us work but equally to our vast amount of functionless so-called “junk DNA”, and even the remnants of ancient viruses that once worked their way into our genomes.
This is Fairbanks’ field of expertise and he is not afraid to offer detail. It is worth persevering for the insight that these analyses offer: because of the way genetic variation accumulates over time, it is now possible to reconstruct humanity’s spread across the globe with astonishing accuracy. DNA evidence shows, for example, that the Andean peoples of Peru are descended largely from “native” women (whose ancestors came from north-east Asia across a land bridge some 15,000 years ago) and, on the male side, from a small group of rapacious Spanish soldiers.
Evolving does a good job of explaining how we know what we do about our origins; but a much better account of what we know is to be found in Ian Tattersall’s Masters of the Planet: The Search for our Human Origins. Whereas Fairbanks is most at home amid our coils of chromosomes, Tattersall is instead a bones man. As befits a curator emeritus of the American Museum of Natural History, he is an expert guide to the fossil evidence. In Masters of the Planet he has drawn on this expertise to produce an authoritative snapshot of the ongoing struggle to understand our evolutionary past.
What is most striking is just how much can be read from a few ancient skulls if you know how. Bipedalism is a case in point: no scientist has seen our putative ape-like ancestors in the flesh, yet they deduce from a host of clues that these ancestors were walking on two legs some 4m years ago. For example, if the hole through which the spinal cord enters is on the underside of the skull, this suggests an upright posture – in quadrupeds, including great apes such as chimpanzees, this hole tends to be more at the back of the skull. (You can work out why this is by going down on all fours: you will find your head naturally positioned so as to be staring at the ground rather than looking forwards – which is not conducive to avoiding sabre-toothed tigers.)
Countless other clues, from toes to hips, help give an idea of how a specimen might have looked when alive. But they leave open the question of why. Coming down from the trees to wander about upright would, as Tattersall points out, have been hugely risky. It meant leaving a way of life that had been successful for millions of years to develop new foraging strategies in the face of the ferocious predators that prowled the grasslands. There are many theories purporting to explain why our ancestors became bipedal, from minimising exposure to the baking African sun to increasing long-distance trekking efficiency. But none seems entirely adequate to explain such a revolution. This is, as Tattersall puts it, “hugely unfortunate”, as everything that has come since – up to and including you reading this article – follows from those first two-legged steps.
Tattersall does an excellent job of showing how we can sketch the story of our origins from the few precious fossil remains, while at the same time not glossing over our ignorance of such crucial details. But the psychologist David P Barash is even bolder in embracing the unknown: his latest book, Homo Mysterious: Evolutionary Puzzles of Human Nature, is a catalogue of the many unresolved riddles of our history.
A surprising number of these mysteries concern female sexuality. The male orgasm, for example, serves a rather obvious seed-sowing function – but what is the point of its female equivalent? The popular hypothesis that such ecstasy enhances the likelihood of a subsequent pregnancy is, Barash informs us, entirely without evidence. The idea that it might motivate reluctant ladies also seems flawed: other animals don’t require an eruption of bliss in order to continue the family line. Perhaps it is simply a “non-adaptive by-product” – an incidental development to which evolution is indifferent?
Barash doesn’t think so, preferring to believe that it is more important than that. But in what way remains a riddle – and only one of many posed by the female body. Scientists cannot explain, for example, why women have prominent breasts even when they are not suckling children. Other mammals don’t. Yes, of course, men are drawn to these protruding sacks of fat – but why? No one knows, though theories abound.
As Barash points out, most books about science are accounts of what we know – threatening to give the impression that all the hard work is done. In doing the opposite and writing about the gaps in our knowledge, he hopes to inspire the next generation of Darwins and Dawkinses to take up lab coats in the pursuit of truth. The book is not a white flag in the face of the unknown but a call to arms, suffused with confidence that nature will ultimately give up all her secrets.
Some might think it imprudent of Barash to admit to so many gaps in the evolutionary account of humanity, given that religious fundamentalists are ready to exploit them for their own ends. But it is just this willingness to admit what we do not know, combined with the conviction that we nonetheless can and will know it, that marks out the scientific method. And we might celebrate the fact that this method, through revealing our simian history, has brought us far enough as a species to see just how far we have come.
Stephen Cave is author of ‘Immortality: The Quest to Live Forever and How It Drives Civilisation’ (Biteback/Crown)
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