Sex Is Driven by the Impetus to Change
Ask any biologist—sex seems like a waste. It’s costly: Think of the enormous energy that goes into producing a peacock’s spectacular fan-shaped tail, apparently meant to entice a female to mate with him. And it seems inefficient: Sex allows us to pass on only half of our genes, and fully half the species (males) can’t bear children. Evolution is unsentimental, so those costs must bring benefits. The usual answer is that, by reshuffling genes with every generation, sex creates new genetic combinations, detaches beneficial mutations from harmful ones and gives a species a degree of evolutionary flexibility. It keeps genes in the pool that might not be of use today, but might save a creature’s descendants from plagues, pestilence, and parasites.
All that is probably true, but the thesis has one flaw. While the benefits of sexual reproduction tend to be subtle and become evident only over many generations, its costs are heavy and immediate. To understand sex completely, we need an explanation that goes back to the primordial soup of very early complex organisms and the immediate survival pressures they were under. Damian Dowling, an Australian evolutionary biologist, set forth last year with colleagues Justin Havird and Matthew Hall in the journal . It proceeds from the simple fact that single-celled bacteria and archaea, known as prokaryotes, never indulge in sexual reproduction. They have some sex-like behaviors, including making bodily contact to exchange genes—sometimes called “bacterial sex.” But they do not reproduce sexually; they proliferate simply by dividing
