The Accidental Species: Misunderstandings of Human Evolution, by Henry Gee, University of Chicago, RRP£18/$26, 224 pages

Why Dogs Hump and Bees Get Depressed, by Marc Bekoff, New World Library, RRP£13.99/$15.95, 320 pages

The Gap: The Science of What Separates Us from Other Animals, by Thomas Suddendorf, Basic Books, RRP£19.99/$29.99, 352 pages

A Natural History of Human Thinking, by Michael Tomasello, Harvard, RRP£25.95/$35, 192 pages

You might think that we humans are special: no other species has, for example, landed on the moon, or invented the iPad. But then, I personally haven’t done those things either. So if such achievements are what makes us human then I must be relegated to the beasts, except in so far as I can catch a little reflected glory from true humans such as Neil Armstrong or Steve Jobs.

Fortunately, there are other, more inclusive, ideas around about what makes us human. Not long ago, most people (in the west) were happy with the account found in the Bible: we are made in the image of God – end of argument. But the theory of evolution tells a different story, one in which humans slowly emerged as a twig on the tree of life. The problem with this explanation is that it is much more difficult to say exactly what makes us so different from all the other twigs.

Indeed, in the light of new research into animal intelligence, some scientists have concluded that there simply is no profound difference between us and other species. This is the stance taken in new books by Henry Gee, palaeontology editor of the leading scientific journal Nature, and by animal behaviour expert Marc Bekoff. But other scientists of equal eminence argue the opposite: that new research is finally making the profound difference between humans and animals clear – and two of them, the psychologists Michael Tomasello and Thomas Suddendorf, have written new books purporting to tell us exactly what it is.

But first, there are no obvious physical features to explain our successes. Such useful below-the-neck traits as bipedalism and opposable thumbs are too widespread (many birds, for example, are both bipedal and have opposable digits – albeit claws rather than thumbs). And just pointing to our large brains won’t work: they might be three times the size of the brains of chimpanzees but elephants’ brains are three times bigger again. Of course, elephants have bigger bodies too, leading some to think that we might have the highest ratio of brain size to body size. However, that honour actually belongs to shrews and ants.

Some determined researchers drew up a new measure, according to which brains grow larger as body size increases but not in direct proportion. It turns out that, with enough tweaking, a scale can be developed according to which humans come out as the brainiest. But the real lesson we might draw from this is how desperate we are to demonstrate that we are special, and how hard this is to do with any rigour.

For Gee, this shows that our obsession with our uniqueness is folly. “There is nothing special about being human, any more than there is anything special about being a guinea pig or a geranium,” he writes in his persuasive book The Accidental Species: Misunderstandings of Human Evolution. We only believe we are so exceptional, he argues, because we believe that we are the pinnacle of evolution. But this is a misunderstanding: we are just one twig in the thicket, and we could easily have never sprouted at all.

Gee is good at explaining how fossil evidence has been (mis)interpreted to fit that famous picture of man rising from the ape, growing taller and wiser with each step before culminating in us. The reality, he points out, is very different: until recently (no later than 50,000 years ago) there were many species of humans across the world. Some, such as the Neanderthals, had brains at least as big as ours; while others, such as the diminutive “hobbit” found on the Indonesian island of Flores, were more closely akin to the apes.

In such a world, Homo sapiens would have appeared much less exceptional, and our close connection to other species more obvious. Some of these other humans disappeared through natural disasters – a volcanic eruption in the case of the hobbit population – whereas others might have been driven to extinction by us. So if our twig stands out, it might be only because we have ruthlessly pruned the rest of the branch.

This would fit with the biologist Marc Bekoff’s view of modern humans. What sets us apart, he argues, is that “we’re the only animals who cook food, and no other species is as destructive of its own and other species”. His latest work Why Dogs Hump and Bees Get Depressed: The Fascinating Science of Animal Intelligence, Emotions, Friendship and Conservation is a collection of his blog posts and essays that aims to show that other animals are every bit as special as we are.

Bekoff’s starting place is what he calls the principle of evolutionary continuity. For too long, he writes, we claimed to be the only species with reason, emotion, consciousness or morality. But we share a long evolutionary history and basic biology with other animals, particularly other mammals. We should therefore expect that “if some mammals experience something, most or all mammals probably do, too.” It would be simply unscientific to expect one twig on the tree of life to be radically different from those on the branches around it.

Like Gee, Bekoff supports his case with examples of altruistic rats, toolmaking crows and evidence of the emotional lives of bees. Towards the end, there is even an account of what appears to be animal spirituality: one group of chimpanzees have been recorded participating in a “waterfall dance”, during which they would stand upright at the water’s edge, swaying rhythmically from foot to foot and stamping for up to 15 minutes.

Bekoff’s central claim – that we are far from standing out as the only complex thinking creatures on earth – is now much less controversial than it was just a few decades ago. His own tireless writing and campaigning have made a significant contribution to this turn. But despite some interesting snippets, this new collection adds little to his excellent earlier books on the moral and emotional lives of animals.

The University of Queensland psychologist Thomas Suddendorf places Bekoff among the “romantics” – those inclined generously to ascribe human-like traits to other animals. Suddendorf himself is keen to avoid being the opposite – a “killjoy” who tries to explain away all evidence of thinking in rats and dogs. In his admirably clear and cogent first book The Gap: The Science of What Separates Us from Other Animals he seeks a middle way that does justice to other species while arguing that there really are important differences between us and them.

What makes this so difficult is our closeness to the other branches on the tree of life as highlighted by Gee and Bekoff. This does not mean that there are no differences between the branches, only that these are differences of degree: we are not the only species with, for example, language – we just have more of it. The same goes for the other features that Suddendorf considers key to our success: mental time travel (thinking about the past and future), theory of mind (thinking about what others might be thinking), intelligence, culture and morality.

Take, for example, the ability to imagine and plan for the future. Monkeys are bad at this – in one case, a group of capuchin monkeys who were fed biscuits once each day would invariably eat their fill then throw the leftovers out of their cage, only to regret this and desperately try to retrieve them when hungry a few hours later. Chimps, on the other hand, demonstrate some foresight and self-control: they can resist the biscuit in front of them if they know doing so will result in their receiving many more biscuits. But the longest any chimp has managed this feat of self-control is eight minutes. Compare this with humans who can delay gratification for days, weeks, or even a whole lifetime in the hope of getting their reward in heaven.

Suddendorf’s book is a fine introduction to this fascinating field and deserves a wide audience; but it is notable that he frequently relies on the research of Michael Tomasello, co-director of the Max Planck Institute for Evolutionary Anthropology in Leipzig. Those seeking the most cutting-edge account might therefore turn directly to Tomasello’s own new book, A Natural History of Human Thinking.

Tomasello has spent a lifetime conducting similar tests on both great apes such as chimpanzees and on humans of different ages, in order to pin down exactly where our capacities differ. In this difficult but rewarding book, he attempts to place these results into a grand theory of how and why these differences evolved.

All of our enhanced faculties, he argues, are about one thing: co-operation. Our great ape cousins are very social – a trait associated with cognitive complexity – but they are mostly competitive within those social groups. At some point in our evolutionary history, he conjectures, early humans were forced to overcome this competitiveness and work together for common goals such as hunting large prey. Such co-operation then drove the development of all those faculties listed by Suddendorf, from understanding others to language, culture and morality. These abilities further support each other, which is why the twig of humanity now stands out so far.

Tomasello makes a good case for our being hardwired to work together: in one study he cites, an adult and a human infant were engaged in a joint effort to get a toy. When the adult suddenly stopped, the child tried various means to re-engage him; whereas chimps just tried to manage the task on their own. In another study, pairs of three-year-old children had to collaborate for a reward; when the reward unexpectedly became available to one child halfway through, he or she nonetheless ignored it and persisted until both were rewarded – needless to say, chimpanzees did not.

Tomasello’s account of how co-operation drove the development of our distinctive intellect is controversial – Bekoff too would point to the growing body of evidence on how other species co-operate. It is also highly speculative: a trait such as co-operation leaves few traces in the fossil record. But it is speculation by a thinker at the top of his field, based on the latest research, and as such is likely to be the definitive statement of human uniqueness for some time to come.

His account also makes me feel better about not having invented the iPad or landed on the moon: it suggests that these are indeed triumphs of the human spirit, but not because they sprang from the minds of lone superhumans. Rather, it is because they are products of the distinctively human practice of putting heads together. And even I can do that.

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Stephen Cave is author of ‘Immortality: The Quest to Live Forever and How It Drives Civilisation’ (Biteback/Crown)

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Letter in response to this article:

Humans have ability to communicate in abstract language / From Mr David Tipping