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Psychologists attend lectures on the Nature/Nurture debate with a certain sense of weary inevitability. This is born of the artificial polarisation of the debate by those with a book to sell or an axe to grind. When I realised that Matt Ridley had, yes, a new book to promote, I settled down for a rehash of the old arguments. It was therefore delightful to hear a speaker who articulated a balanced position in a novel way. This was backed by evidence guaranteed to interest a wide range of biological scientists as well as the general public.

We started with a sweep through the history of the debate, from both a literary and a philosophical viewpoint, which stressed that it has been an issue for writers and educators as far back as the sixteenth century. After a sweep through the derivation of what Galton termed "A convenient jingle of words", and the philosophical divide between the empirical school, represented by Locke, Hume and Mill (Nurture) and the continental naturists such as Hobbes, Rousseau and Kant (Nature), we settled down to a history of the science behind the debate in the last two centuries. While the division of the last 130 years into blocks in which one viewpoint was dominant was a little simplistic, it was nonetheless effective in conveying the fluctuation of scientific fashions in this area, and hinting at the sometimes dreadful political consequences of these skewed beliefs.

First he outlined the period 1870-1920 as "Heredity’s Heyday" which began with Darwin, who wished to emphasise the shocking new truth that humans were part of the animal continuum, touched on Galton and William James and ended with Haeckel’s alarming theories on racial determinism. We then heard the period of 1910-1960 characterised as years in which the view of the child at birth as a tabula rasa or "Blank Slate" was current. In this area psychologists were as dominant as biologists had been over the previous half century, with a coherent case being made for the linking of Freud with Pavlov and the founders of behaviourism, Watson and Skinner. The case for the human as the product and not the cause of society had never been stronger.

Next he outlined the most recent period of 1960-2000 as representing yet another swing of the pendulum. Following the discovery of DNA’s structure in 1953 - an anniversary commemorated in this series of lectures - evidence appeared to accumulate which pointed to innate components of extremely complex behaviour, resulting in the current climate of headlines reporting the discovery of "genes for criminality." The work of Konrad Lorenz, Noam Chomsky and Jane Goodall was all placed in the context of this argument for the innateness of much that makes us human - love, language and society. Finally we were brought right up to date with the selfish gene views propounded by Hamilton, Pinker, Boucher and Dawkins, for whom the body is merely the vehicle that genes employ to reach the next generation.

In the year in which the complete human genome has finally been published there was a timely examination of what this vast potential knowledge might mean for the issue of what makes us who we are. The idea that our unique consciousness and use of language resulted from having many more genes than other organisms - perhaps as many as 100,000 - has been exploded. The total is only 30,000, about the same as mice and a quarter less than rice. Are there therefore too few genes to explain the complexity of human behaviour, bringing nurture back into the picture by default? Is free will in fact the null hypothesis? The idiocy of this philosophy of numbers was sharply pointed up by the pithy observation that, under such a schema the virus would be the J.S. Mill of biology!

The aim of this lecture, after all the scene-setting, was to propound a view which integrates both nature and nurture into a single model. As he pointed out at the beginning of the lecture, as long ago as 1581 Richard Mulcaster wrote "By nature emplanted, for nurture to enlarge" and it is this which forms the basis of his model. However, as well as including the widely recognised feed-forward moderation of the relationship between phenotype and behaviour by nurture, his model also included the feedback mechanism whereby behaviour itself modifies the relationship between the genotype and the phenotype. This incorporates the bi-directional relationship between behaviour and gene expression which is widely acknowledged but rarely stated explicitly in general texts. The neat title of the lecture "Nature via Nurture" was thus arrived at.

The remainder of the lecture expounded this thesis with reference to various examples in which the interaction of genes and experience is observed. An excellent slide clearly illustrated the absurdity of the "gene for every trait" approach often found in populist science reporting. This purported to illustrate the genes for attributes of maleness, which would of course be found on the Y-chromosome. After skimming down the slide, from the gene for the tendency to play air guitar (RIF) past selective hearing loss (HUH) to the love of gadgetry (MAC locus) the audience, or at least that portion of it without a Y-chromosome, chuckled appreciatively.

More seriously, he cited the work of Susan Mineka and colleagues, which provides a neat illustration of Seligman’s preparedness theory whereby a predisposition to a particular behaviour is mediated by a particular experience. In Mineka’s elegant study, a captive-bred monkey with no fear of snakes in shown a videotape of a wild monkey showing terror in response to a snake. The captive-bred animal developed an extreme fear of snakes following the viewing - a clear example of vicarious conditioning. The important element of the study, however, is the control condition, in which the captive-bred monkey sees a videotape of the same monkey showing the same fearful reactions to a flower. This fails to induce a fear of flowers in the subject monkey, demonstrating that there must be both nature (tendency to fear snakes) and nurture (experience of other animals showing fear) for conditioning to occur.

Moving to humans, he cited walking and adoption of gender roles as examples of behaviours which contain strong genetic components (all infants pull themselves up and attempt to walk; boys are more likely than girls to prefer war games) but also require experience (those wobbly steps need practising; boys are more likely than girls to be praised for "tough" behaviour). He is clearly on more controversial ground with the second example than the first, but the point is well made and accessible.

The importance of experience and behaviour in guiding the expression of genes is well illustrated by the examples of critical periods presented here. At a very biological level we have the development of ocular dominance columns in striate cortex which occurs during the first few days of life in mammals. If visual input is absent or comes from only one eye, then this organisation of the brain will not take place and the input from one eye will be permanently disregarded by the brain. The genes determine the organisation but the experience of vision is required for translation of genotype to phenotype - the calibration of the system. The timing of the critical period is known to be affected by a number of genes. For example, a knockout of the GAD2 gene delays it indefinitely, whilst the genetically caused over-expression of a nerve-growth factor (BDNF) causes the premature ending of the critical period.

The imprinting which Lorenz used as such a powerful example of biologically determined behaviour also turns out to have a critical period in which it will occur, and when we turn to humans we find that one of our defining features, language, also has a critical period for development. This is illustrated by the sad examples of children who have been profoundly neglected and deprived of spoken language input, such as Genie. Up until the age of about 13 it appears possible for language to be acquired, but after this point, though words may be acquired, grammar will elude the child. Chomsky’s grammar may be universal but it is not unlimited.

Staying with language, studies of a large family, many of whose members suffer from specific language impairment (SLI) have identified a gene which appears to be important in language development. SLI sufferers have problems with language such as inability to generalise grammatical rules. The members of this family with the problem also carried a mutation of the FOXP2 gene. This gene appears in a different form in humans to all other primates and mammals. It has undergone two non-silent mutations in the last 200,000 years of the human lineage which appear to have been very actively selected for. This may be the gene for complex language but we need to remember that without experience at the correct time it is never fully expressed.

There was some interesting speculation on the role of the AVPRIA gene which is a vasopressin regulator. An insertion on this gene causes vasopressin to be expressed in different regions of the brain. Both the insertion and the differential expression of vasopressin are found in prairie voles which form pair bonds which involve paternal involvement with offspring. Neither are found in other vole species in which paternity begins and ends with conception. Humans carry a similar insertion in the AVPRIA gene to prairie voles, but there are substantial individual differences in the length of the gene. Whether this is a factor in the formation of stable relationships is clearly a question for future research . . . and a whole new section on the dating agency questionnaire!

Finally the issue of criminality was addressed. The question of whether criminals are born or made has influenced penal policy for centuries, and the answer would appear to be that both genes and childhood maltreatment are vulnerability factors for a criminal record. While a Dutch family with a history of antisocial behaviour in its male members showed a specific mutation in the gene for monoamine oxidase A (MOA-A), an enzyme which breaks down the neurotransmitter serotonin in the brain, this mutation has never been found outside of this particular family. However, there are two forms of the promoter for this gene, one highly active and the other less so. The genes themselves have no impact on behaviour, but the combination of a less active MAO-A promoter and childhood maltreatment produces a hugely increased risk of criminal conviction.

The point was made that the best predictor of an outcome will depend on the prevalence of both the gene and the behaviour: when few people read behaviour is the best predictor of myopia, with mass education genes become a better predictor. Matt Ridley never allows speculation to run away with him, and just as we were tempted down the "Aha! A gene for . . ." route, the evidence for the critical role of nurture was presented as a counterbalance. The role of genes in permitting learning and the equal role of experience in altering gene expression were repeatedly emphasised and made accessible through well-chosen examples.

One of the themes of this lecture, which made it stand out from many such contributions was that it did not shy away from the philosophical, and indeed theological implications of the viewpoints discussed. As well as facing the issue of biological determinism head-on, even in the controversial area of sex differences, Matt Ridley pointed out in his conclusions what many social learning theorists fail to acknowledge: that social determinism is just as inimical to free-will as the genetic kind. Leibniz’s monads were experiential as well as biological and Freud was a determinist to just as great an extent as Chomsky. The unfashionable truth that meritocracy is genetic determinism was clearly stated, while evolution, and beyond that technology, was identified as the greatest promoter of free-will. Stephen Fry, who suggested that he call his book "Nature, Nurture and Nietzsche" would not have been disappointed.

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