If I were leafing through Prospect wondering where to begin, I would probably pass over this article. Given its theme??nature or nurture??I would expect to be bored. And for several reasons: for the confused arguments that are mobilised by those who want to prove either that our character (behaviour, personality) is entirely, or mostly, genetically determined or entirely, or mostly, environmentally determined; for the straw men each party conscripts to represent the views of its opponents; for the banality of middle positions which remind us that both nature and nurture contribute to our being the kind of creatures we are; and, most of all, because the warring parties tend to walk straight past the places where the really interesting questions about human nature are to be found.
Much of the excitement of the nature versus nurture debate comes from the nastiness that it brings out in the participants. The spectacle of charismatic communicators at each others? throats almost compensates for the tedium of a muddled debate. In his recent onslaught (The Blank Slate), Steven Pinker accused those who minimise the role of genes in the shaping of the human mind, in explaining differences between individuals or determining their attainments in IQ tests, life and everything else, of being in thrall to an ?anti-life, anti-human? abstraction.? The genophobes can be just as rude. When EO Wilson launched ?sociobiology??whose central notion is that behaviour and society are ?the extensions of genes that exist because of their superior adaptive value??he was accused, in a letter in the New York Review of Books from Stephen Jay Gould, Richard Lewontin and others, of reviving ideas that provided the basis for ?the eugenics policies which led to the establishment of gas chambers in Nazi Germany.?
Yet often the similarities between the two sides are more important than their differences. The progressive environmentalists, who emphasise nurture, are as determinist as the reactionary hereditarians, who emphasise nature. And both parties tend to overlook most of what it is to be human. Matt Ridley?s book Nature via Nurture admirably defuses this simplistic antithesis. Though Ridley does not take the obvious next step and reject the terms of the ?nature versus nurture? debate altogether, he does provide ammunition for those of us who feel that neither naturians nor nurturists properly engage with?to echo his subtitle??what makes us human.?
The book is a wonderful achievement: rigorously argued, steeped in the primary scientific literature and impressively up to date. Ridley?s argument is that recent genetic research has shown us not only how genes influence behaviour but also how behaviour influences genes. Genes are designed to take their cue from nurture: ?the more we lift the lid on the genome,? he writes, ?the more vulnerable to experience genes appear to be.? Gene expression can be a consequence as well as a cause of what we do. ?The adherents of the ?nurture? side of the argument have scared themselves silly at the power and inevitability of genes, and missed the greatest lesson of all: the genes are on their side.? We pick the nurture that suits our nature: ?having ?sporty genes? makes you want to practise sport; having ?intellectual genes? makes you seek out intellectual activity. The genes are the agents of nurture.?
Ridley illustrates his thesis with many striking examples. Here is a handful taken at random. Darlene Francis and Tom Insel transplanted embryonic mice of one genetically pure strain into the wombs of mice of another genetically pure strain and found that the transplanted mice took on behavioural characteristics?such as hesitation before plucking up courage to explore?of the strain of the mother in whose womb they had been fostered. In other words, the intra- uterine environment can override genetic propensities. Josh Huang investigated the production of brain-derived neurotrophic factor (BDNF), a key mediator of the impact of experience on brain growth and organisation during development and learning. He created genetically-modified mice which produced a double dose of BDNF. When he reared them in the dark he found that they developed normal visual function. This was quite unlike normal mice which, if reared in the dark during a critical growth period, cannot see properly. Genes, it appears, may substitute for aspects of experience. The vast literature on language acquisition suggests that we have an innate ability to learn by experience, a natural instinct for acquiring the relevant nurture: we are genetically programmed to use environmental drivers to develop. Learning, far from being the opposite of instinct, is itself an instinct and what we learn is determined not only by what we are exposed to but also by the genetic tuning of our brains, which are prewired to extract the most relevant experiences from the environment. Even the most primitive form of learning?the acquisition of conditioned reflexes?depends upon dopaminergic neurons which are genetically regulated. This function can be altered by knocking out the relevant gene. By a series of ingenious experiments, published a couple of years ago, Josh Dubnau and Tim Tully demonstrated that different genes are active in the acquisition and retrieval of memory in the fruit fly.
The Berlin wall dividing naturians and nurturists has been given another knock by studies of intra-uterine influences on development which have discredited the notion that nurture acts postnatally and nature prenatally, and the belief, dear to ?blank-slate? progressives, that nurture is manipulable and nature is not. Gilbert Gottlieb found that ducklings who were made mute by operations on their vocal cords while they were still in the egg did not respond specifically to the maternal call of their own species, unlike other ducklings, and concluded that this was because they had not heard their own embryonic voices before hatching. It would seem that our apparently instinctive behaviour is shaped by our experiences even before we are born. David Barker hypothesised from a pathbreaking series of observations on the influence of birthweight on cardiovascular health in middle age and beyond, that intra-uterine deprivation caused certain developmental switches to be thrown and a ?thrifty phenotype? to result. This phenotype is unable to cope with the metabolic consequences of postnatal plenty and develops cardiovascular disease. Prenatal environmental influences have even been invoked to explain sexual preference (see Philip Hunter, Prospect November 2002). Growing in a womb previously occupied by at least one male tenant appears to have two effects on a male embryo: lighter birthweight and increased propensity to homosexuality. Ray Blanchard, who made this observation, suggests that this is because the previous male tenant provokes a maternal immune reaction to genes that are expressed only in males, among them a gene called PCDH22 which is on the Y chromosome. This wires a bit of the brain that is peculiar to males and its absence may prevent the wiring that is associated with attraction to female bodies.
Ridley?s insistence on the interaction of genes with the environment in determining the finished product of an organism is a reaction to the resurgence of the hereditarians following a long eclipse after the second world war. Francis Galton, who launched the modern nature/nurture debate in the late 19th century, wrote: ?There is no escape from the conclusion that nature prevails enormously over nurture? My fear is that the evidence may seem to prove too much and be discredited on that account, as it appears contrary to all experience that nurture should count for so little.?
He came to this conclusion on the basis of twin studies and these have provided powerful ammunition for the naturians. From 1945 until the late 1970s, however, Galton?s notion of a genetic basis for human characteristics, and even the use of twin studies, was regarded with disdain and indeed moral repulsion, not least because this was one of Dr Mengele?s preoccupations. Twins, however, provide such enticing natural experiments?and occur with such frequency?that studies of them have proved irresistible. By comparing dizygotic twins (womb-mates derived from two fertilised eggs who do not have the same genetic composition) with monozygotic, or identical, twins (womb-mates derived from a single fertilised egg who have precisely the same genetic make-up) and also by comparing both kinds of twin reared apart and brought up together, it has seemed possible to disentangle the respective contributions of nurture and nature to the formation of personality.
Such studies have produced results that go beyond the expected high correlations for physical characteristics and propensity to disease. Thomas Bouchard found that the correlation on scores for religious fundamentalism for identical twins reared apart (same genes, different environment) is 62 per cent, while that for fraternal twins reared apart (different genes, different environment) is 2 per cent. The figures for broader measures of religiosity are 58 per cent and 27 per cent respectively; and for right-wing attitudes they are 69 per cent for identical twins reared apart, while there is no correlation for fraternal twins reared apart. In other words, even prototypically ?cultural? things such as religion and political beliefs appear to be influenced by one?s genetic make-up.
But there are reasons for not getting overexcited by these findings. First, it is not clear how many attempted correlations the whole literature contains and, even more important, the extent to which there is a publication bias in favour of positive findings which may conceal the contribution of chance. There are innumerable possible human characteristics and populations which might be studied. Second, categories such as ?religiosity? or ?right-wing attitudes? are gross simplifications of higher-level aspects of human consciousness, which encompass a vast range of individual modes of thinking and feeling. And third, there is no reason to assume that these cultural phenomena are linked directly to genes rather than the (high) phenotypical correlations between the identical twins: having very similar physical characteristics may make them more likely to have or choose similar experiences.
Not getting too excited is increasingly justified by the tantalising story of the unsuccessful search for ?genes for? characteristics such as intelligence and the even more disappointing failure to identify the ?genes for? disorders such as autism and schizophrenia, despite their high degree of heritability?in the case of autism, up to 90 per cent. Ridley?s critique of the notion of a ?gene for x? is one of the many glories of his book. His summary of our current understanding of schizophrenia could not be bettered: ?A century after the syndrome was first identified, the only two things that can be said for certain about schizophrenia are that blaming unemotional mothers was plain wrong, and that there is something highly heritable about it. Many genes clearly influence susceptibility to schizophrenia, many may respond to it in compensation, few seem to cause it.?
This is a serious blow to naturians and makes the hope of identifying genes for something that is rather more ontologically dubious??general intelligence??seem yet more forlorn. Random searches through the genes of intelligent people to find ways in which they differ consistently from average people have so far turned up just one decent statistical correlation and more than 2,000 no-shows. If, as Ridley argues, ?genes are the means by which nurture expresses itself, just as surely as they are the means by which nature expresses itself,? the gene hunt will be beset by noise?or, more precisely, there will be no scientific basis for a principled distinction between signal and noise. The heritability of IQ, for example, depends strongly on socioeconomic status. To make things more confusing, this dependency is nonlinear. Living on a few thousand pounds a year can severely affect your performance in IQ tests but living on ?40,000 or ?400,000 a year makes little difference. In other words, once environment has reached a certain minimum standard, innate capacity starts to matter more.
Such observations in Ridley?s book should move the debate on. He has shown that there is a way of incorporating insights from both naturians and nurturists. Nature via Nurture is not merely a place in the middle of the road but a position of genuine synthesis. His book should be required reading for journalists; for those in the humanities with so much to say about scientists about whose work they have so little knowledge; as well as for those lecture-circuit charismatics who betray their scientific calling in pursuit of popular excitement. Still, I don?t think Ridley has moved the debate on far enough.
There are several reasons for taking a more radical step beyond nature/nurture. The first is that the two terms are so ill-defined. For Galton, ?nature? was the contribution of heredity to our personality, intelligence, achievements and a variety of physical and mental characteristics. A century or so later, heredity has boiled down to the roles of genes. But this has not resulted in clarification. Above the level of molecular biology, the notion of a ?gene? has become increasingly complex. The chapter in which Ridley addresses the ambiguities of this slippery word is an expository tour de force. He considers seven possible meanings of gene as used in different contexts: a unit of heredity; an interchangeable part of evolution; a recipe for a metabolic product; a disease averter or health giver; a development switch; a unit of selection; and a unit of instinct. These different ways of seeing a gene are neither mutually exclusive nor precisely mappable on to one another. There is another problem: genes have been invoked not only to account for the differences between human beings but also (by sociobiologists and evolutionary psychologists) to explain human nature in general. This has created new muddles between genetic variation as the determinant of individual personality and the human genome as a constraint on human nature in general. Those who believe that there are genes that make human males violent are often unclear whether such genes are part of a common male inheritance designed to assist life in the wild or are present in only a subset of very bloodthirsty males.
Gene-eyed evolutionary psychologists are reminiscent of those professors in the Academy at Lagado who tried to separate the sunbeams that had gone into making a cucumber. Worse: evolutionary psychology not only attempts to break down the cucumber into its individual sunbeams but imagines that it can measure their relative intensity and their separate contributions to the tastiness of individual slices.
The unsatisfactory consequences of the naturian habit of segmenting the rich manifold of human consciousness into a manageable number of parameters to be measured are also borne by nurturists purporting to correlate digitised bits of ?the environment? with digitised bits of the person. Nurturists, however, have additional difficulties of their own. The work of David Barker and others has pushed the empire of nurture backwards in time to intra-uterine life and, indeed, to the moment of conception. The post-conceptional range of nurture seems limitless. ?Nurture? is usually taken to encompass things that are not only, as Galton said, ?innumerable,? but also almost ludicrously heterogeneous: exposure to weather and illness, parental care (smacks and hugs), interactions with siblings and peers, watching television, training and education, the accidents of life, and so on.
Even less clear is how, beneath gross and uninformative classifications, we are to think of these often quite abstract environmental ?factors? doing their work, and whether we should think of them as ?factors? at all; or how we should take account of the fact that?just as the human race has collectively created an environment of artefacts, institutions and rules?so individual humans contribute to making their own environment from quite early on. Take a very ordinary example: the ?learning behaviour? exhibited by a woman who, at the age of 30 embarks on a course of self-improvement. She decides she will attend evening classes in 2004 to learn German. In order to make this possible, she devotes part of 2003 to stockpiling babysitting tokens so that she won?t have to miss any lessons. Her subsequent ability to speak German will clearly, in part, be owing to the environment she has found herself in; but this is an environment she has created, or at least requisitioned, for herself. Are we to include this kind of thing?which makes up most of human life?in the ?environmental? factors that ?explain? what she has become? If we are, then the scope of ?environment? has expanded beyond something that is encountered as given to parts of the world which the individual has created.
Although Ridley notes that Piaget saw ?cognitive development neither as learning, nor as maturation, but as a combination of the two, a sort of active engagement of the developing mind with the world,? he still seems wedded to an externalist account of human life and behaviour. ?Nature via nurture? is just as determinist as the claim that ?it is all in our genes,? or the environmentalist Pavlov?s assertion that ?the real cause of every activity lies outside of man.? For Ridley?s understanding of ?what makes us human? is resolutely biological. In this respect, he is rather similar to Richard Dawkins, who acknowledges that consciousness frees humans from the tyranny of genes. Dawkins has advanced the notion of the ?extended phenotype,? which includes social organs such as institutions and forms of behaviour, and he suggests that cultural evolution takes place through self-replicating ?memes,? units of cultural inheritance.
But this simply replaces the distinctively human with biological?and Darwinian?thought, from which mind, intention, self-consciousness and agency, the active shaping of one?s life, are absent. Such ?biologism? does not acknowledge the profound difference between, say, a gene as ?a device for extracting information from the environment? and a woman who so orders her affairs as to be able to attend evening classes in the future. The difference is between the largely physical environment of beasts and the largely abstract nexus of meaning, engaged by a self-conscious agent, that is the context of ordinary human life. Biologism ignores the extent to which we shape ourselves in response to customised circumstances.
While Ridley rightly observes that one is no more or less free if one?s behaviour is accounted for 99 per cent by the environment and 1 per cent by genes or vice versa, he does not draw the correct conclusion from this: that all nature/nurture explanations of human behaviour are inadequate. This is because they are rooted in biology and no biological account, which must treat people as organisms, can find a place for human freedom. He is aware of this and attempts, unsuccessfully, to find free will within his biological framework by replacing what he calls linear with circular causality, in which an effect influences its own cause. But his observation that genes are ?steeped in circular causality? shows how little relevance this idea has to the freedom that characterises humans.
Ridley?s sophisticated story, just as much as the simplifications of evolutionary psychology, sociobiology and behaviourism, elides the huge gap between humans and other animals. He does this by attributing human characteristics to non-human organisms, and vice versa. This is most striking in the amusing anthropomorphisms in which Ridley frequently indulges. In his discussion of the microscopic worm Caenorhabditis elegans?which has no brain and the princely total of 302 neurons?he speaks of the beast showing "flexible learning," and discusses the difference between "social" worms that "go to school" (are housed in a petri dish with other worms) and those that are "kept at home," and how they develop different adult "personalities." This rampant Disneyfication allows him to move easily between "memory" in fruit flies and memory in humans. Interestingly, when he expresses the view that pair bonding in prairie voles may not be entirely different from human love, he cites in support of his view what is in fact a potent piece of contrary evidence?an excerpt from A Midsummer Night?s Dream. It should not be necessary to point out that the fact that prairie voles do not write about love, or write like Shakespeare about love, says more about the differences between us and prairie voles than biology can begin to take account of. His account of the research suggesting that the ability to form long-term attachments (signifying love rather than just sex) in humans and rats depends "on the length of a piece of DNA text in the promoter switch at the front of a certain receptor gene" is animalomorphic about humans and anthropomorphic about rats.
Ridley delivers abundantly on his title, Nature via Nurture, but he does not do so on his subtitle, Genes, Experience and What Makes us Human. What makes us human?creatures unique among all creatures in leading, rather than merely living, our lives?is importantly different from the genetic or environmental influences that make C elegans C elegans or a prairie vole a prairie vole or even a chimpanzee a chimpanzee. Of course, there are many underpinning biological (and indeed physico-chemical) mechanisms in common, but biological mechanisms are not the whole story, or even an important part of the story, of human lives and what makes one life go badly and another go well.
The distinctively human story began several million years ago when, for a variety of reasons (discussed in my book The Hand: A Philosophical Inquiry into Human Being), people started parting company from the other beasts. From then on, what was absent in most animals and only fleeting in higher primates became increasingly central in humans: self-consciousness stabilising into selfhood; instinctive behaviour evolving into agency, regulated by often quite abstract customs and rules; tools sustaining a network of culture in which partially collectivised experience forms the basis for the creation of a world of signs, symbols and artefacts distant from nature; sentience becoming objectivised and pooled as knowledge; uncertainty becoming the basis of institutionalised inquiry, and so forth. Even sophisticated "biologistic" accounts of humans sideline this, and tend to see humans as organisms, rather than as people whose behaviour is primarily governed by considerations for which there is no equivalent in the animal kingdom. They will, therefore, like their environmentalist or geneticist predecessors, be several million years out of date, overlooking the thousands of generations of cultural development, the self-transformation of humanity, made possible by the second-order awareness that first arose in that remote past when hominids set out on their lonely path.
This is not to deny our biological origins. We were not dropped by God from the sky into the natural world. But we are our origins only to the extent that an adult is a neonate. To seek "what makes us human" in the places where we took off from nature is like trying to find on the launchpad a rocket that has already been travelling for several million years.
