Does this make people prisoners of the way their brain is wired ?

The genetic illusion WHAT is man ? Philosophers have debated this question for millennia , reaching no very serious conclusion . Lately , however , philosophy has become rather less fashionable than genetics , which is in the throes of a hugely expensive effort , known as the Human Genome Project , to answer the same question . This project is already showing great promise . It should produce many medical benefits . But it will also throw up some ethical dilemmas . Should humans be genetically engineered ; should insurers have access to customers ' genetic make - up to assess their risk of disease ? And , in the longer run , it is in danger of creating a philosophical misconception of its own: that men 's actions are determined by their genes , not by their own free will .

It is not the geneticists who are at fault . The trouble is that other people often read too much into what geneticists do . When a geneticist asks what man is , one obvious answer is: " 99% a chimpanzee " . This is the percentage by which a person 's DNA appears to match that of his nearest non - human relation . What it is to be human is , in that sense , crowded into 1% of the 3 billion genetic " letters " that go to make up a person 's genetic material - - the human genome .

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Reading those 3 billion letters is the task of the genome project , which expects to list all of them within the next few years in the hope of producing new forms of medical diagnosis and treatment ( see page ) . But this is not merely a matter of working out what the genes are . Biologists also need to interpret the messages genes carry , and how those messages interact to build a person . If and when the interpretation is completed , humanity will know its biological self better than was conceivable as little as two decades ago .

After such knowledge Yet anticipating that interpretation risks recapitulating mistakes that have dogged genetics since its inception . The subject got off to a bad start when the work of its founding genius , Gregor Mendel , was ignored for almost 40 years . The period of this ignorance - - the last decades of the 19th century - - was marked by the growth of eugenics . This movement proposed to improve humanity by a process tantamount to selective breeding . One strand of it , however , begat America 's sterilisation and selective immigration laws of the 1920s, and ultimately led to the Nazi death camps .

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Another strand - - concerned with the measurement of human intelligence - - rapidly degenerated into a vacuous debate between those who thought intelligence to be largely inherited and those who believed it to be a product of a child 's early environment: nature versus nurture , as the argument came to be known . By the time real scientific genetics started its careful , limited experiments on plants and fruit flies and fungi , ideological camps were already established , and prepared to pounce on any result that supported their point of view . Conversely , geneticists with particular points of view were not above making up results to support their own ideologies .

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There is a real danger that this could happen again . The reaction against genetic explanations that followed the excesses of eugenics has lost much of its steam . There seems to be particular public interest in scientific results that purport to show that this or that aspect of human behaviour is under biological control . There is , it is said , a gene for " thrill seeking " . Male homosexuality , one result suggests , is inherited down the maternal line . The brains of homosexuals are different from those of heterosexuals . The brains of dyslexics are different from those of people who can read easily . Few of these results have emerged from the genome project itself . But , as time goes by , some such information undoubtedly will , and will strengthen the idea that people 's will is not as free as western philosophers have liked to suppose . Or , as it is often put , that biology is destiny .

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Yet this would be an error . Clear limits exist to normal human behaviour , and such limits are obviously genetic . People do not , for instance , eat grass and moo . They do not , except in novels by Edgar Rice Burroughs , swing through the trees . But it is nevertheless true that they could choose to do these things if they wanted to , at least for a time .

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The respectable scientific case against free will is a physicist 's case - - that every outcome is an inevitable consequence of the arrangement of matter that immediately preceded it . This is not , however , a biologist 's case . And it is certainly not a geneticist 's case . For " biology is destiny " carries a second , unspoken , premise: " genetics is biology " . The conclusion that follows is: " therefore genetics is destiny " . Sometimes it is . Men with a fault in the appropriate gene will be colourblind without exception . Usually , though , things are more complex . Height is certainly under genetic control , but genes do not explain why young Japanese are taller than their fathers . The cause is a change of diet . And nutrition is just as " biological " as genetics .

About a dozen genes are reckoned to control height . Brains are built and regulated by thousands of them . And in addition to this the scope for environmental effects on brain development , and therefore on behaviour and intelligence , is both enormous and commonplace . It is known as learning .

The complexity of the way the brain develops and functions , and the interaction between genes and environment that is responsible for it , will certainly be illuminated by the genome project . Genes will emerge that , if present in one form rather than another , or present in particular combinations , predispose people to behave one way rather than another . Other genes will cause only those predispositions appropriate to a particular environment to develop . All such predispositions will be expressed in the same way - - in the actual wiring of the nerve cells that make up the brain .

Does this make people prisoners of the way their brain is wired ? This question is best addressed by asking not whether it seems difficult for someone to make a particular choice , but whether it seems impossible . Sometimes it clearly is . Certain diseases genuinely rob people of choice . Accidental brain damage can have the same effect . If neurobiology ultimately comes to show that the way someone 's brain is wired really does limit their scope for choice in a given situation to no choice at all , then so be it . But even when the genome project is completed , the science that could come to that conclusion will still be a long way off - - and just how far off can be imagined by thinking how much a person differs from a chimpanzee , yet how similar is their DNA . So much complexity from so little difference . Genetics has suffered before from a mountain of speculation being built on a molehill of knowledge , and humanity has suffered as a result . For now there is no reason to abandon the belief that people control their own actions - - and should be held responsible for them .

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