Communications of the ACM
Why Sex?
Photo Researchers, Inc.
At the heart of the theory of evolution lies a conundrum.
Most people think of natural selection in terms of "survival of the fittest." And when it comes to asexual organisms, that catchphrase is pretty much on the mark. The fittest individual in a population will (by definition) have the most offspring, and over generations, the number of these offspring—all identical to their common ancestor—will grow exponentially and gradually take over the population, crowding out less fit individuals.
When it comes to sexual reproduction, however, the fittest genotypes do not survive down the generations. If nature comes up with an exceptionally fit individual, there is no way to preserve that individual's makeup intact in the next generation. Each offspring gets only half of the fit parent's genes, and over generations, that parent's contribution becomes more and more diluted. Instead of hanging on to the winning hands, sexual reproduction shuffles the deck with each generation, seemingly driving the population towards a steady mediocrity. On the face of it, sexual reproduction seems like a pretty stupid idea.
And yet, sex is everywhere...
From Simons Foundation
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