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thumbnail image of amourous coupleessay: The Advantage of Sex

The topminnow
breeds both
asexually and
sexually at
different times.
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Real-world evidence  

In the years since Hamilton's simulations, empirical support for his hypothesis has been growing. There is, first, the fact that asexuality is more common in species that are little troubled by disease: boom-and-bust microscopic creatures, arctic or high-altitude plants and insects. The best test of the Red Queen hypothesis, though, was a study by Curtis Lively and Robert Vrijenhoek, then of Rutgers University in New Jersey, of a little fish in Mexico called the topminnow.

The topminnow, which sometimes crossbreeds with another similar fish to produce an asexual hybrid, is under constant attack by a parasite, a worm that causes "black-spot disease." The researchers found that the asexually reproducing topminnows harbored many more black-spot worms than did those producing sexually. That fit the Red Queen hypothesis: The sexual topminnows could devise new defenses faster by recombination than the asexually producing ones.

It could well be that the deleterious mutation hypothesis and the Red Queen hypothesis are both true, and that sex serves both functions. Or that the deleterious mutation hypothesis may be true for long-lived things like mammals and trees, but not for short-lived things like insects, in which case there might well be need for both models to explain the whole pattern. Perpetually transient, life is a treadmill, not a ladder. end of essay
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