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A Most Private Evolution

Dumb designs for sex: Evolutionary biology walks on the weird side

Maybe female seed beetles have their own what-the-bleep exclamation. Even for insects, it’s difficult to imagine any other reaction to a male Callosobruchus maculatus beetle’s sex organ, which has spikes.

“It jumps to mind as something quite dumb,” says Göran Arnqvist, an evolutionary biologist at Uppsala University in Sweden, who for much of the past eight years has studied seed beetle sex.

Male beetles of several Callosobruchus species have sharp edges on their sperm-delivery organs. The females’ ducts grow a bit of extra toughening but not enough to make sex safe from the risk of injury. After many tests, Arnqvist has concluded that the genital excesses aren’t good for the species as a whole. These seed beetles would have less-damaging sex — and would produce more babies — if males lost their edges.

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