Almost 99 per cent of our species’ functional genes are identical to those of a chimp. Yet as the evolutionary biologist Armand Leroi points out in his documentary series What Makes Us Human?, which concludes tonight, people and chimpanzees are not easily confused.
The genes that vary between us and our closest animal cousins may be few, but the differences they explain are vast. They account for our big brains, high intelligence, language and complex culture. All these human qualities have been advanced as answers to Leroi’s question but a relatively small number of genes underlie them all.
Only a handful of these are known. Leroi offers two examples: ASPM, involved in brain development, and FOXP2, which is critical to language. The search for others is among the most exciting in science and US researchers revealed a good new candidate, HAR1, this week, which probably influences brain development.
The identification of these genes is a source of wonder, with the power to explain how our species has become what it is. By understanding them we can also aspire to treat and prevent disorders that occur when they go wrong. ASPM, for instance, malfunctions to cause a brain condition called microcephaly, and is the basis of an embryo screening test.
This field of study, though, invariably ignites controversy. If evolving genes have given us our distinctive human brains and behaviour, they might also explain qualities such as intelligence and aggression that differ between humans. This notion is often fiercely resisted, amid allegations of genetic determinism and even racism.
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But such charges often stem from misunderstandings of what this science implies. The ASPM gene is a good example. Bruce Lahn, of the University of Chicago, has found evidence suggesting that this gene has been evolving recently in humans.
About 10 per cent of us have two copies of a new variant, and another 50 per cent have one copy. As the gene is involved in brain growth, it is possible that it is being selected because of a positive effect on intelligence.
Yet far from being a “gene for” intelligence, its function remains unknown. Even if it does affect intellect, it is certain to be one of many factors, both genetic and environmental, that play a part. No serious scientist would claim that it has a narrow deterministic effect.
This was demonstrated in the first part of What Makes Us Human? The patently bright Leroi took the ASPM test himself and was revealed to have “bog standard” variants. If the gene has any impact, it is a small cog in a bigger machine.
Another gene that illustrates this is called MAOA. Research suggests that people with one version are predisposed to antisocial behaviour, but only if they were maltreated as children. Rod Lea, a New Zealand scientist, was attacked last week for racial stereotyping after noting the high frequency of this variant among male Maori. Local newspapers talked of a “warrior gene”. Yet Lea never suggested that the Maori are programmed to be violent. The link between the MAOA variant and aggression depends on a tough environment: to say it is common is not to say that violence will be, too. Lea was investigating whether the gene might also influence other social problems among the Maori, particularly high rates of smoking. The misguided row is threatening what could prove to be beneficial work.
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We are the products of our genes, as Leroi’s series makes clear. But it does not follow that they control us, or that recognising their importance is a cause for concern. A misguided fear of determinism risks holding back research that promises to transform understanding of how genes shape the human body and mind, and how we might correct the malign side of their influence.
What Makes Us Human? Channel 4, tonight, 8.10pm. Mark Henderson is Science Editor of The Times