Friday 28 January 2011

The chasm that separates great apes from humans

Jon Cohen’s new book reminds us that, for all the claims that apes and human beings are ‘98.5 per cent the same’ in terms of genetics, there is still an unfathomable gap between us.

Today we are often told that us ‘arrogant’ human beings need to get off our anthropocentric pedestal. We are not as special as we think; we are ‘just another ape’. Peter Singer, the so-called father of the animal rights movement, claims that the great apes - that is, orang-utans, gorillas, chimpanzees and bonobos - are not only our closest living relatives; they also possess many of the characteristics that were once considered to be unique to humans.

When I met one of the world’s foremost primatologists, Frans de Waal, in 2005, to discuss his book Our Inner Ape: The Past and Future of Human Nature, he told me: ‘Genetically, we are 98.5 per cent identical to chimps and bonobos, and mentally, socially and emotionally we are probably also 98.5 per cent identical. We love to emphasise that little difference that exists and cling to it and make a big deal out of it, but the similarities vastly outnumber the differences.’ Similarly, Deborah Fouts, co-director of the Chimpanzee and Human Communication Institute based in Central Washington University, although conceding that ‘[chimpanzees] haven’t built a rocket ship to the moon’, asserts that ‘we’re not that different’.

In his new book Searching for What Makes Us Human, in Rainforests, Labs, Sanctuaries, and Zoos, American science journalist Jon Cohen suggests that it might now be time to emphasise the differences between us and our evolutionary cousins.

He writes: ‘There is something fundamentally backward about the “almost human” rubric for chimps. From everything I can tell, no chimpanzee looks at a human and wonders: is this where I came from? Nor do chimps ponder the possibility that we represent where they are heading. Yet humans from every culture look at chimpanzees and see hints of their primitive selves.’

Cohen recounts a number of tales from his travels around the world, when he met both with chimps and their researchers. His journey includes world-renowned genetics labs, rainforests in Uganda, sanctuaries in Iowa, and experimental enclaves in Japan. At times, the book frustratingly reads like a collection of tangentially related articles, where Cohen’s argument is often hidden or lost; but nonetheless there are many interesting insights into the world of ape research.

For instance, cutting-edge genetics research has shed some light on the conundrum of the one per cent difference between the genes of chimps and humans. ‘The nearly-identical molecular makeup does not lead to nearly identical organisms’, Cohen points out.

The differences between humans and chimps are vast. ‘We have bigger and more complex brains, fully-fledged language and writing, sophisticated tools, the control of fire, cultures that become increasingly complex, permanent structures in which to live and work, and the ability to walk upright and travel far and wide’, Cohen writes. And we differ not only in terms of our behaviour and how we live, but also in terms of our anatomy and susceptibility and resistance to different diseases. Chimps miscarry much less frequently than humans, and males ejaculate far more sperm. ‘A one per cent genetic difference accounts for all this?’, Cohen asks.

The publication of the draft of the chimpanzee genome in September 2005 may have provided us with some of the answers. ‘Just as the research team provided the best validation yet of a one per cent difference, it also revealed the most dramatic evidence of the figure’s limitations’, says Cohen, explaining: ‘To begin with, the number does not factor in the many stretches of DNA that have been inserted in or deleted from the genomes… But more striking still, the chimpanzee genome project highlighted the importance of the biological knobs that control gene expression.’

In Not a Chimp, Jeremy Taylor similarly argues that the genetic gap between humans and chimpanzees is far larger than molecular biology first indicated. Some of the important differences between the genomes of chimps and humans are in the regulation of gene expression. So a small change can make an immense difference.

Having investigated the ape-language field for my book Just Another Ape?, I was especially interested in what Cohen had to say about apes’ purported ability to acquire human-like language. During one of his journeys, Cohen met two of the stars of the ape-language world: the bonobo Kanzi and his half-sister, Panbanisha. He writes: ‘If they have language, I did not witness it. If a three-year-old human showed as little response to what I said, I would think the child had a hearing problem or was psychologically impaired.’

The 1960s and 70s were the heyday of ape-language research, but the field imploded in the 1980s after Columbia University researcher, Herbert Terrace, published the findings of his attempts to teach the chimp Nim Chimpsky American Sign Language (ASL). Not only did Terrace conclude that Nim was incapable of creating sentences; his team also analysed films of other high-profile ASL-using apes, including Washoe the chimp and Koko the gorilla, and decided that apes had a ‘severely restricted’ ability to learn more than ‘isolated symbols.’ There was no evidence of them being able to create sentences.

The field became the butt of jokes, Cohen points out, quoting the linguist Noam Chomsky: ‘It’s as likely that an ape will prove to have a language ability as there is an island somewhere with a species of flightless birds waiting for humans to teach them to fly.’

Cohen rightly concedes that apes do communicate with each other in the wild, but their communications by no means reach the status of language. He writes: ‘Chimpanzees, as far as scientists can tell, only vocalise about the here and now. They do not talk about yesterday or tomorrow, their dreams or fears, loves lost or sought – all of which would require using words as symbols.’

At the Wolfgang Köhler Primate Research Centre in Leipzig, Germany, Cohen was given a tour by its director, Josep Call. Call and his team have carried out comparative research on two-year-old human children and adult chimps and orang-utans, and have found that human children significantly outperform apes on social cognition tasks even at this young age. This shows that humans are not just social, Call says, but ‘ultra social’.

It is our unique ability to connect with other minds that has allowed us to advance through cumulative cultural transmission. Michael Tomasello, director of the Leipzig centre’s department of developmental and comparative psychology, told Cohen: ‘If you raise a human baby on a desert island outside of any kind of culture, that child’s cognitive abilities as an adult would be very similar to other apes. What’s really different is something in the direction of culture. All of the things we consider our highest achievements, including language, symbolic mathematics and social institutions like governments and universities… these are cultural products. This isn’t one person’s brainpower. These are collective efforts.’

Because chimpanzees cannot teach or truly imitate, their cultural learning is severely limited. As Call told Cohen, it would be possible for a single chimpanzee to invent all the achievements of other chimpanzees within its lifetime. ‘A smart human could not invent a car or even the thing you are writing with’, Call told Cohen. ‘Or imagine if you had to invent algebra in a lifetime and invent Arabic numerals. Without that given to you by your culture, you’re not going to get there.’

Back in the US, Cohen spoke to David Premack, the man who came up with the concept of ‘Theory of Mind’. He has carried out extensive comparative research on chimps and humans, concluding that only humans can teach and correct themselves. Premack writes: ‘It is no coincidence that humans both practise and teach, whereas other species do neither. A species that practises but does not teach – that corrects itself but does not correct others – will probably never be found. Nor will a species of the opposite kind, one that teaches but does not practise, [one that] corrects others but not itself.’

Although the field of primate research is littered with anthropomorphism – as Premack told Cohen, too many of his former colleagues were ‘chimp huggers’ who ‘confused chimps with humans’ – there has been some fascinating research in recent decades, and key theoretical breakthroughs have been made. Cohen is lucky to have had the opportunity to meet so many of those who have been at the forefront of these innovations, and to discuss their findings and insights with them.