There’s something about sex that seems to inspire whimsy. The scientific literature on how it all began is spiced with clever turns of phrase, witty asides, and the occasional risque double entendre. perhaps the strain of accounting for such an absurd way of making babies goes to the heads of even the sober men and women of science.
You’d think there would hardly be cause for such exercise about the original reason for sex. After all, the problem was considered pretty well solved 30 years ago. Sex was said to be good for the species, says Richard Michod, a 41-year-old professor of ecology and evolutionary biology at the University of Arizona in Tucson and one of the key figures in the current debate. By sex, of course, he means the mating of genetic material from two individuals to produce one with a new combination of genes. By ensuring that offspring were slightly different from their parents, sex increased the chances that a species would produce a new, improved model capable of surviving environmental changes or of getting the jump on a rival or predator. It provided genetic variability, so sexual populations evolved faster, and that was that. It was in all the textbooks, says Michod.
In the mid-seventies, however, evolutionary biologists began to question that conventional wisdom. Chief among the worriers was John Maynard Smith, a professor of biology at the University of Sussex in England and, dare one say it, a seminal figure in the field. He was troubled that the standard explanation for sex invoked a slightly dubious mechanism (dubious in his view, anyway) known as group selection.
The classic example of group selection in action is the animal that gives a warning cry to alert the group to a dangerous predator and thereby puts itself at risk. Why does self-sacrificing behavior enter into a discussion of sex? Because no organism in its right mind would opt for sex with another organism as a way to create offspring. It’s too darned expensive, genetically speaking.
Most higher organisms that go in for sexual reproduction package their genes into pairs of chromosomes (we humans have 23 such pairs). But any sexually reproducing organism throws half its genes overboard when it makes sex cells--that is, eggs or sperm--because its sex cells contain only one chromosome from each chromosome pair. (This is called the haploid, or halved, condition; the union of egg and sperm in sexual reproduction restores the diploid, or paired chromosome, condition.) Thrifty asexual organisms, on the other hand, transmit all their genes to the next generation.
