The Red Queen_ Sex and the Evolution of Human Nature - Matt Ridley [21]
Attempts to explain sex have since proliferated like libidinous rabbits. They present an unusual spectacle to the observer of science. Most of the time, scientists are groping around in a barrel of ignorance trying to find a fact or a theory, or to discern a pattern where none has been seen before. But this was a rather different game. The fact – sex – was well known. To explain it – to give sex an advantage – was not sufficient. The proffered explanation had to be better than others. It is rather like the gazelle running faster than other gazelles, rather than running faster than cheetahs. Theories of sex are two a penny and most are ‘right’ in the sense of making logical sense. But which is most right?25
In the pages that follow you will meet three kinds of scientist. The first is a molecular biologist, muttering about enzymes and exonucleolytic degradation. He wants to know what happens to the DNA of which genes are made. His conviction is that sex is all about repairing DNA or some such molecular engineering. He does not understand equations, but he loves long words, usually ones he and his colleagues have invented. The second is a geneticist, all mutations and Mendelism. He will be obsessed with describing what happens to genes during sex. He will demand experiments, such as depriving organisms of sex for many generations to see what happens. Unless you stop him he will start writing equations and talking of ‘linkage disequilibria’. The third is an ecologist, all parasites and polyploidy. He loves comparative evidence: which species has sex and which does not. He knows a plethora of extraneous facts about the arctic and the tropics. His thinking is a little less rigorous than others’, his language a little more colourful. His natural habitat is the graph, his occupation the computer simulation.
Each of these characters champions a type of explanation for sex. The molecular biologist is essentially talking about why sex was invented, which is not necessarily the same question as what sex achieves today, the question the geneticist prefers to address. The ecologist, meanwhile, is asking a slightly different question: under what circumstances is sex better than asex? An analogy might be the reasons for the invention of computers. The historian (like the molecular biologist) will insist they were invented to crack the codes used by German submarine commanders. But they are not used for that today. They are used to do repetitive tasks more efficiently and quickly than people can (the geneticist’s answer). The ecologist is interested in why computers have replaced telephone operators but not, say, cooks. All three may be ‘right’ on different levels.
The Master-copy Theory
The leader of the molecular biologists is Harris Bernstein of the University of Arizona. His argument is that sex was invented to repair genes. The first hint of this was the discovery that mutant fruit flies unable to repair genes are unable to ‘recombine’ them either: recombination is the essential procedure in sex, the mixing of genes from the two grandparents of the sperm or egg. Knock out genetic repair and sex stops too.
Bernstein noticed that the tools the cell uses for sex are the same as it uses to repair genes. But he has been unable to convince the geneticists or the ecologists that repair is more than the original, long-superseded purpose of the machinery sex uses. The geneticists say the machinery of sex did indeed evolve from the machinery of gene repair, but that is not the same thing as saying sex exists, today, to repair genes. After all human legs are the descendants of fishes’ fins. But they are designed, nowadays, for walking, not swimming.26
A quick digression into molecules is necessary here. DNA, the stuff of genes, is a long, thin molecule that carries information in a simple alphabet of four chemical ‘bases’, like Morse