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Among these cave insects, the females evolved to have penises — twice. The reasons challenge common assumptions about sex.
Some species have the equivalent of many more than two sexes, but most do not. A new model suggests the reason depends on how often they mate.
The oldest law of genetics says that gametes combine randomly, but experiments hint that sometimes eggs select sperm actively for their genetic assets.
The mathematical concept of parity and the fatal flaw of serial multiplication can help explain why having two sexes usually works better than having one or three.
Sex might help natural selection purge excessive mistakes from our genes.
Asexual reproduction can produce twice as many offspring as sexual reproduction without the hassle of finding and courting a mate. So why do most complex animals have two sexes? Why not three?
Nature offers species a panoply of ways to determine an organism’s sex. That flexibility suggests we need not be concerned about losing sex chromosomes, but it raises the question of why such a fundamental property is so variable.
Microscopic creatures called bdelloid rotifers have thrived without mating for millions of years. How they did it could reveal why sex is so essential for almost everyone else.
An insight borrowed from computer science suggests that evolution values both fitness and diversity.
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