Science explains: the shape of the penis
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Evolutionary science suggests that the phallus' shape serves to flush out any possible competitors sperm.
The latest research suggests the mechanics of sexual intercourse and the shape of the human penis evolved as a countermeasure to the infidelity of our female forebears. Men may not be aware of it, but during sex they may be instinctively using their penises as "sperm displacement devices," says evolutionary psychologist Todd Shackelford of Florida Atlantic University.
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