The argument that some behaviour is “in our genes” is distrusted by the left. Too often it is used to whitewash terrible injustices. Yet it cannot be entirely dismissed. Certain patterns of behaviour and thought, such as the faculty of language acquisition, are very clearly a part of our genetic inheritance as a species. The instinct for justice itself appears to arise spontaneously in small children. The escape from the idea that genes determine our fate is not to pretend that they have no influence, but to come to understand that they can have many different, often conflicting influences, even within the same people and certainly within populations. This is true both of their effects on behaviour and on bodies.

Biology is a science that deals with variations. There is no one perfect type of a species. Diversity, in this sense, is not just something to aim at but something necessary for a population to flourish. The idea that natural selection works only on mutations is a deeply misleading oversimplification. It is much more likely to alter the proportions of an already existing mixture of genes. What is more, game theory shows that the balance of advantage will shift as a result of the shift in a gene’s frequency. With very few exceptions, such as the change that Noam Chomsky postulates makes possible the complexity of human syntax, few mutations are going to be so overwhelmingly advantageous that they drive out all other variants. More often, if any one variation becomes dominant, there will be an advantage for its opposite. “Normal” is thus a shifting, fuzzy category.

This is especially true of the genes which can influence human behaviour and emotional predispositions. Not only is the chain of causation from gene expression to behaviour unimaginably complex, it is also profoundly affected by outside circumstances. Identical twins, who share the same DNA, are not identical people, because they cannot entirely share the same life and experiences.

What science can do, under these circumstances, is to look for correlations between DNA sequences and observable behaviour. The correlations can, at best, give pointers towards where causes might be found. The latest effort has been to see if there is a genetic cause for homosexuality and the result is clear. There isn’t.

Using a data set of nearly half a million people, of whom 27,000 reported same sex contact, researchers found – in their own words – “In aggregate, all tested genetic variants … do not allow meaningful prediction of an individual’s sexual behaviour”. There are five loci which appear to have a measurable, though far from decisive, influence on sexual preference. Some are also involved with the sense of smell, and one is associated with male pattern baldness.

This leads to perhaps the most interesting feature of the research: it not only shows that there is no clear genetic cause for same sex attraction, but that the attraction itself does not form a coherent whole. Some of the genetic variations weakly associated with same sex behaviour are different in men and women. In place of the old idea that there might be a single cause for a single pattern of behaviour, there is now an understanding of multiple causes for varying patterns of behaviour. In place of a single scale of sexual attraction as posited by Kinsey, in which desire for the same sex and opposite sex are linked so that more of one means less of the other, the researchers suggest that these are independent variables. Diversity is good in itself and humans are more – much more – than the sum of their genes.

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