Granted that recorded history is only a moment in evolutionary time and that music-making is not part of our fossil record, the fact that the ability to compose melodies has survived for as long as it has must have some significant evolutionary function. Otherwise, it would have declined to become a trivial part of the gene pool. Given that its incidence is so regular, it is unlikely to be a random or spontaneous event. The numbers of musicians, cross-cultural similarities, its early onset and its historicity, all suggest that music-making is significant. We may argue, then, that music-making is either a by-product of some other adaptive process, or adaptive in its own right.
This paragraph is lifted from Jim McKnight's book, except that I have substituted music for homosexuality. And, in strict sociobiological terms, why not? One could spend an enjoyable afternoon dreaming up contributions which music might make to reproductive fitness. Perhaps it binds a community together, helping to ensure a more secure upbringing for its offspring. Perhaps music brings about sexual as well as emotional arousal, in individuals or groups, and so more offspring result. Or perhaps musicians have a stronger libido than those of us who are tone deaf, are more successful at attracting sexual partners, or make more caring parents. Throw in a few speculations about how all this worked in hunter-gatherer bands 50,000 years ago, and some first-hand accounts of sex 'n' drugs 'n' rock and roll today, and you are well on the way to a book proposal.
What the proposal would lack is science. So far as I know, there is no research dedicated to teasing out which of these evolutionary scenarios might stand up. But there could be. There is ample evidence that musical ability is partly genetically determined; and the appeal of music is one of the great human mysteries, surely deserving of investigation.
True, the analogy with homosexuality is imperfect. The intellectual puzzle which took McKnight's fancy is how to account for a behaviour which is of no obvious reproductive advantage. For among exclusively homosexual males - he is not concerned here with explaining the endurance of same-sex attraction in women - there is no chance of passing on their genes. So if, as he assumes, their behaviour is under genetic influence, why does it not disappear from the population? But that hardly seems enough to account for the attention the puzzle has attracted from researchers. That is in some ways as much of a puzzle as the one McKnight wants to solve.
He tells us several times in this book of the opposition he faced when he let it be known that it was this question he wanted to answer. But there seem to have been many researchers equally devoted to identifying the biological correlates of same-sex attraction: hormonal, neurophysiological or genetic; and others who have tried to account for the persistence of putative genes for homosexuality.
Since the recent reports of Simon LeVay on brain anatomy and Dean Hamer's group on a possible genetic marker, the biological view of homosexuality has gained ground. Neither of these studies is totally persuasive, and both still await replication, but both are streets ahead of most of what went before. Here McKnight covers much the same ground as LeVay's own recent book with the complementary title Queer Science, though less stylishly. He offer a conscientious review of a large array of inconclusive, unrepeatable, or methodologically flawed studies of hormone action, intra-uterine environments, inheritance and sexual and reproductive behaviour.
This is followed by a discussion of evolutionary scenarios which might account for the persistence of homosexual genes. As McKnight says, all of these "are inferential and the hypotheses we generate are propositional rather than empirical in nature". In truth, they often have the authentic sociobiological quality of an intellectual parlour game - quite fun as long as they are not taken too seriously. The specific scenarios are explained clearly enough, though the exposition is not helped by McKnight's repeated switch between the assumption that there is a "gay gene" and his disavowal of a belief in it. It is hard to decide if this is a justified effort at simplifying the logic of the various arguments about balanced polymorphism and inclusive fitness which might solve his puzzle, or a wish to have his cake and eat it. Either way, by the end it is hard to feel that we are much further forward.
I have no quarrel with McKnight's contention that the weight of evidence is against anyone who would defend a purely constructivist account of sexual orientation. Of course it matters that we are creatures with a biology, and with an evolutionary history as well as a life history. But moving beyond that truism is hampered by the proliferation of speculations on details of our evolutionary past which are forever lost to us, and by the disinclination of contemporary human populations to restrict their behavioural repertoire to that of rats or even monkeys. Despite McKnight's sterling efforts to achieve clarity, much of the discussion reinforces his suggestion that the literature on homosexuality is "a vast confusion from which few clear answers emerge".
His remedy is to focus on the "far more fundamental" question of why homosexuality persists, rather than simply asking how it comes about. After reading this book, I am not convinced that this helps. If we do arrive at a point where there is persuasive evidence that homosexuality is partly genetically determined, no doubt evolutionary theory is flexible enough to account for this. But then, in the hands of a sociobiologist, evolutionary theory can account for almost anything. McKnight suggests this is the direction in which social psychology is going in order to recover lost confidence in its ability to cope with the diversity of human behaviour. On this showing, I am not sure if the renewal of confidence is justified.
Jon Turney is senior lecturer in science communication, University College London.
Straight Science?: Homosexuality, Evolution and Adaptation
Author - Jim McKnight
ISBN - 0 415 15772 2 and 0 415 15773 0
Publisher - Routledge
Price - £45.00 and £14.99
Pages - 218