Most people think of masturbation as a poor substitute for sex. The question is, why is it a substitute for sex? For most species, it doesn’t seem to achieve any kind of evolutionary purpose. Or does it?

Historically, masturbation was considered sinful because it did not—it could not—produce any offspring. That’s not a socially progressive viewpoint, but evolutionarily it’s spot on. Masturbation doesn’t have a clear evolutionary advantage, and it does waste the body’s resources. While it’s understandable that people, and animals, might masturbate due to a sexual urge, why does masturbation relieve the urge? Wouldn’t evolution favor creatures that only get aroused for a potential mate?

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A fun possible evolutionary justification for masturbation comes from scientists studying marine iguanas. The marine iguana mating scene consists of harems kept by the biggest, meanest males on the beach. Naturally, there’s some sneaking around going on. Sneaky smaller males can tempt females to mate with them, but these sessions depend on timing. If the larger male interrupts the couple before the act is over, the smaller male could get hurt without getting any babies out of the encounter. Scientists noticed that smaller males often engaged in an odd behavior before they went out to find a female. They’d grip the rock beneath them and rub against it. The motion was subtle, but unmistakable. Soon the smaller male was ready to go, and could get the mating done faster than a male who hadn’t prepared himself.

So the urge to masturbate might not be just about enjoyment—it might be a way to make sure everyone can get off quick before her husband comes home. That probably doesn’t make it less sinful, though.

Image: Diego Delso, License CC-BY-SA 4.0

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