GUILT-FREE intercourse may, as Philip Larkin wrote, have begun in 1963, but sexual reproduction has been around a good deal longer than that. About two billion years ago single-celled organisms began exchanging and mixing up genetic information in ways modern biologists recognise as rudimentary forms of sex—though it would be well over a billion years more before animals evolved nervous systems that would let them derive any pleasure from it. Yet the question of why sex exists at all remains troublesome. A creature which reproduces asexually passes on all of its genes to each of its progeny. One that mates with another, by contrast, passes on only half of them. On the face of things that is a huge selective disadvantage. There must therefore, evolutionary biologists believe, be equally huge compensating benefits.
Two ideas exist about what these might be. One is that the genetic variety sex creates prevents parasites and pathogens evolving a single, optimum technique for exploiting a host species. This is the “Red Queen” hypothesis, an allusion to a character in “Through the Looking-Glass” who had to run as fast as she could to stay in the same place. The other idea is...Continue reading
Source: Science and technology http://ift.tt/1RnHFXD
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