As I write, machines around the world are chewing up human chromosomes and spitting out the raw DNA sequence at an astounding rate of 5 billion bases a year. The four nucleotides that make up the sequence of DNA – adenine, guanine, cytosine and thymine – are represented by their initial letters, A, G, C, T. If we take each of these as equivalent to a letter of the alphabet, the machines are producing text roughly as long as 18 copies of The Origin of Species a day. By the time you read this, the project will be nearly done, though it may take another year to align the bits of sequence and fill in the gaps.
As the most visible (and expensive) product of Big Biology, the human genome project has understandably attracted much public attention. The excitement stems not from decoding the genome of a complex organism – that has already been done for fruit flies and roundworms – but from hopes that having the human DNA sequence will help us cure disease, genetically engineer our own and other species and, above all, tell us what makes us specifically human. These aspirations are flamboyantly expressed on the dust flap of Genome: The Autobiography of a Species in 23 Chapters: ‘The human genome, the complete set of genes housed in 23 pairs of chromosomes, is nothing less than an autobiography of our species … we, this lucky generation, are the first beings who are able to read this extraordinary book, and to gain hitherto unimaginable insights into what it means to be alive, to be human, to be conscious or to be ill.’
Genome is among the first of what will certainly become a flood of books explaining human genetics to the public. Because much of the ‘autobiography’ is still in test tubes, however, Ridley spends less time showcasing the genome project than recounting the last decade of research in human genetics. His stories are at once instructive and infuriating. For each nugget of science, Ridley also includes an error or misrepresentation. Some of these derive from poor scholarship: others from his political agenda. Ridley’s genetic determinism is so implacable that he admits virtually no environmental influence on our human make-up, and his right-wing politics lead him to slant the implications of the research he discusses and to deliver annoying homilies against big government and environmentalism. In the end, Genome is more soapbox than synopsis.
Ridley structures the book eccentrically, with its 23 chapters numbered (and titled) to correspond to our chromosome pairs. From each chromosome, he picks a single gene to inspire an essay on a big question – ‘History’, ‘Fate’, ‘Stress’, ‘Sex’, ‘Free Will’ and so on. Despite this bizarre organisation, it is possible to extract plenty of up-to-date information about genetics. It will be news to many, for example, that 97 per cent of our genome is ‘genetic junk’, a palimpsest of useless DNA from ancient viruses, self-replicating remnants of genes no longer functional, and ‘jumping genes’ that spread regardless of the welfare of their carriers. As Ridley observes, ‘our genomes badly need worming.’ There are further intriguing lessons about genetic conflict – between the sexes, between the genes within a genome, and between parasitic bits of DNA and the chromosomes they seek to colonise. Indeed, rather than a harmonious parliament of genes, our genome looks to Ridley like a Bosnia of opposed interests.
His stories sound good, but all too often stray from the scientific straight-and-narrow into more dubious territory. In fact, the reader without a strong background in genetics and the theory of evolution will have trouble separating fact from fiction. The problems can be seen by taking a close look at the chapter on ‘Intelligence’. Here Ridley revisits a perennial question: to what extent is our intelligence determined by our genes as opposed to our environment? This question has provoked intellectual disagreement for over a century, beginning in 1884 with Francis Galton’s Hereditary Genius, continuing through the eugenics movements of the early 20th century, and culminating in the loudest recent salvos, Stephen Jay Gould’s The Mismeasure of Man and Richard Herrnstein and Charles Murray’s The Bell Curve.
Given the inflammatory nature of the topic, and the powerful sociopolitical questions it raises, it would pay a writer to tread gingerly here. Will understanding the genetics of intelligence help science to make us smarter? Or, if there are no scientific nostrums, can we restructure society so as to use our collective intelligence more efficiently?
The seriousness of these questions, together with the dearth of hard evidence, has produced debates fuelled largely by opinion. Whether one finds nature or nurture to be the predominant factor seems, in fact, to depend on one’s upbringing. A 1968 analysis of US experimenters studying the genetic basis of IQ differences between blacks and whites showed a strong correlation between the authors’ conclusions and their backgrounds: older investigators with less-educated parents and more ancestors coming from abroad, for example, found less genetic influence on racial difference. These are turbulent waters, but Ridley wades in boldly, determined to demonstrate the hegemony of the genes.
He begins on the right note by observing that ‘intelligence’ is a slippery notion that can be defined and measured in many ways. He immediately bypasses this difficulty, however, choosing to define intelligence as whatever is measured by IQ tests. This is encapsulated in the hereditarians’ favourite variable, g (‘general cognitive ability’), which measures correlated performance across several tests, is strongly related to scholastic achievement, and remains fairly constant over an individual’s lifetime. Many have balked at equating intelligence with performance in standardised tests, but Ridley does not break stride: ‘let us accept this plainly foolish definition of intelligence as the thing that is measured by the average of several intelligence tests – g – and see where it gets us.’ Where it gets us is to Ridley’s preordained conclusion that whether we are smart or dumb depends largely on our genes. He never returns to the foolishness of g, which in all later discussion is considered actually to be intelligence.
It is important to realise that the genetic contribution to variation in intelligence among members of a population (‘heritability’) differs from the contribution made to an individual’s intelligence by his or her genes (‘inheritability’). In principle, heritability can be measured: for a given trait in a given population, it is the proportion of the total observed variation among individuals attributable to variation in their genes. (The remaining variation, attributable to ‘environmental effects’, is the amount of variation in the given trait found among genetically identical individuals.) Inheritability, on the other hand, is a loose concept, referring to how important genes are in producing a trait in a single individual; this cannot be measured, and is not equivalent to heritability. The number of limbs found on a human individual, for example, has a strong genetic basis and is thus extremely inheritable. But the heritability of limb number among individuals is nearly zero, because such variation as does exist – e.g. that caused by thalidomide or accidents – is almost entirely of environmental origin.
Confusingly, while reviewing the IQ data, Ridley goes back and forth between these two notions of genetic causation, ultimately telling us, incorrectly, that ‘half of your IQ was inherited.’ What he really means is that half of the observable variation in IQ within a population is due to genetic variation among its members. Ridley notes correctly, however, that estimates of heritability are limited to the group under study, and say nothing about the basis of IQ differences among ethnic or socioeconomic groups, which typically experience different environments.
The conclusion that IQ has a substantial heritability comes largely from work on pairs of identical twins reared either together or apart. As they share the same genes, these twins can in principle be used to separate the effects of nature and nurture. When raised together, members of such pairs show a higher correlation of IQ than do fraternal twins or normal siblings. This correlation may represent not shared genes, however, but shared environments: there are fewer differences in the way we treat a pair of identical twins than there are in the way we treat other children. Nevertheless, when identical twins are reared in separate homes, the correlation between their IQs barely changes, implying that the postnatal environment has little effect on ‘intelligence’.
In the past, most twin studies have suffered from methodological and interpretative problems (see Not in Our Genes, by Richard Lewontin, Steven Rose and Leon Kamin) which may have inflated estimates of the genetic contribution to IQ. Ridley’s conclusion that IQ has a heritability of around 50 per cent rests, however, on more recent studies by Thomas Bouchard and his colleagues at the University of Minnesota. The experimental programme described in their publications seems far sounder than that of earlier researchers, and the conclusions of Bouchard and Co may well be correct. But I suspect the issue may be much less fully resolved than Ridley would have us believe, not least because of Bouchard’s refusal to allow some colleagues access to his primary data. Such access, customary among scientists, is essential for evaluating publications on controversial topics that present only a broad summary of results. Considering the historical problem of investigator bias and the serious flaws uncovered in studies once considered legitimate, I believe that – for the time being – the Minnesota studies cannot be properly evaluated. (These studies, by the way, also show large genetic contributions to variation in many other aspects of behaviour and personality.)
After addressing the general genetic contributions to IQ, Ridley homes in on an ‘intelligence gene’ that seems to dwell on chromosome 6. As in most mapping of human genes, the localisation begins by the discovery of a number of ‘marker genes’, whose DNA sequence varies from person to person. A group of people is then surveyed simultaneously for variation in these markers and variation in a particular trait – in this case, the g statistic. If variation in g correlates with variation in a marker, one has evidence (discounting occasional spurious correlations) that the marker is somewhere near a gene affecting IQ. Because each marker is associated with many nearby genes, a correlation is only the first step in finding the gene of interest. One must then use other methods to navigate the surrounding genetic territory.
This technique has allowed Robert Plomin and his colleagues to localise what they consider to be an ‘intelligence gene’ – a factor affecting the variation in g scores in a sample of Ohio schoolchildren. Unfortunately, Ridley assumes that the marker used by Plomin (a gene called IGF2R) is the actual gene affecting IQ. He speculates in detail about how such an unpromising gene might modify intelligence (the product of IGF2R helps transport proteins around the cell), but such gymnastics are probably fruitless. IGF2R is much more likely to be a landmark than the final destination.
It is doubtful, however, whether Plomin’s intelligence gene even exists. Because of problems with statistics and sampling, nearly every report of a ‘behaviour gene’ located in this way – including those supposedly associated with schizophrenia, manic depression, criminality and alcoholism – has been retracted or called into question when later investigators failed to replicate the results. A famous example is Dean Hamer’s ‘gay gene’, announced with much fanfare in 1993, when his group found an association in 40 families between a marker on the X chromosome and male homosexuality. Because of the high political stakes and levels of public interest, Hamer’s results immediately hit the headlines, followed quickly by the publication of his popular book, The Science of Desire: The Search for the Gay Gene and the Biology of Behaviour. The expected uproar ensued: many gays rejoiced that homosexuality could no longer be seen as a sinful choice, and some conservatives spoke darkly of pre-emptive abortion. Since 1998, however, two independent research groups have failed to find any evidence for Hamer’s gene, which now seems likely to be an artefact of sampling. Unsurprisingly, the press has largely ignored these later studies.
Ridley does not address the implications of genetic studies of IQ. In reality, there aren’t many, unless one wants to ensure the survival of the smartest through selective breeding. In practice, the best one can do is to determine whether IQ can be boosted by social engineering or by altering educational methods – policies that have nothing to do with genetics. Citing the failure of Head Start programmes among young children to produce more than temporary increases in IQ, Ridley implies that such programmes cannot overthrow the dictatorship of the genes. But ‘heritability’ does not mean ‘inevitability’, and Head Start is only one of countless other remedies. For centuries, diabetics were doomed by their genes – until insulin came along in 1921.
Like Ridley’s previous two books, Genome tries to popularise the discipline of ‘evolutionary psychology’, which holds that virtually all human traits were the direct products of natural selection on our ancestors, and that current environments have little effect on our genetic legacy. Evolutionary psychology is deeply controversial because of its continual reliance on untestable assertions about human evolution and its insistence on the primacy of biology over culture in determining our behaviour. Ridley does his best to promote the programme by either dismissing environmental influences or subsuming them into the genome. He notes, for example, that ‘mood, mind, personality and behaviour are indeed socially determined, but that does not mean that they are not also biologically determined. Social influences on behaviour work through the switching on and off of genes.’
This assertion is occasionally true, but more often false. Social influences begin with sense-perception. Hearing and seeing, for example, do not involve the switching on of genes, but instantaneous electrical impulses that release stored neurotransmitters. Subsequent behaviours – anger, pleasure and other types of mood and thought – similarly involve the release of stored chemicals, not the activation or inactivation of genes. Certainly, mood, mind and personality are ‘biologically determined’ in the sense that they involve our brain and body, but the genes act at a long remove, having given us physiological systems free from direct genetic control.
As the book wears on, Ridley’s political views become increasingly intrusive, as he dismisses concerns about mad cow disease (blaming the whole affair on the British Government), genetic engineering of crop plants and global warming, which is seen as a ‘synthetic crisis’. He properly abhors enforced eugenics among humans but, curiously, does not consider the question of genetically modifying helpless and sentient animals. Selective breeding of cows, for instance, has already turned them into udders on legs, unable to stand properly and prone to arthritis and mastitis. Who knows what further suffering will be visited on these animals when we can manipulate their genes at will? But even when discussing human eugenics, Ridley cannot resist pushing his libertarian agenda: ‘Eugenics is like any other programme that puts the social benefit before the individual’s rights. It is a humanitarian, not a scientific crime.’ These ‘humanitarian crimes’ presumably include taxation, handgun prohibition and mandatory speed limits.
Such libertarianism clashes with his extreme genetic determinism: how can we exercise individual choice if we’re prisoners of our genome? Ridley believes, however, that ‘we feel and demonstrably are free,’ and so devotes his last chapter to reconciling genetics and free will. Struggling to resolve this contradiction, he calls on ‘chaos theory’, a mathematical theory based on the fact that, in some complex systems, small differences in starting points yield huge differences in outcomes (the classic example involves the development of weather systems). The discussion turns rather cloudy at this point, but Ridley concludes that slight differences in your environment can make enormous differences in your behaviour. But our choices do not become free simply because we lack the information to predict them: nobody claims that weather has free will because it is hard to forecast. Finally, realising that he has made little headway in his philosophising, Ridley beats a quick retreat into Newspeak, asserting that ‘freedom lies in expressing your own determinism, not somebody else’s.’
The mapping of the human genome will certainly produce substantial scientific and social advances, but can it really tell us what it is to be alive, conscious and human? This is doubtful: we already have the complete sequence of the drosophila genome, but not an inkling of what it is to be a fly. There are two problems here. The first involves the road that leads from DNA to a human being. At one end stands the genome of a fertilised egg: at the other a Homo sapiens. In between is the immense black box of development which hides the complex and unknown ways in which genes interact with each other and with their environment. The intricacy of such interactions, only now starting to be unravelled by developmental biologists, guarantees that an understanding of how genes produce individuals will not be gained in our lifetime, and probably not in our children’s.
More important, understanding the subjective phenomena of consciousness and emotion – surely important parts of being human – cannot rest solely on the reductionist strategy of sequencing genes. Everything that makes us human must be consistent with our genes, but solely in the superficial sense that we can do only what our biology allows us to do. This does not make genetics the unique key to our humanity. Consider three traits that might be seen as uniquely human: romantic love, religious belief and fear of death. Genes contribute to building a brain that makes these feelings possible, but to say that the genes for ‘love’ are those involved in brain development is to engage in unproductive buck-passing. Like free will, ‘being human’ is in many ways an emergent property, requiring analysis at levels higher than that of genes. Ridley is simply operating on the wrong plane when he claims that ‘what we call personality is to a considerable degree a question of brain chemistry.’ This is trivially true, but will not be much help in understanding personality. Turning the tables on Ridley, one might note that, like all material entities, genes must conform to the laws of physics. But this does not mean that what we call genetics is ‘to a considerable degree a question of’ physics.