Female Muscovy ducks have evolved a convoluted mechanism for keeping unwanted males at bay

An extraordinary sexual arms race that has played out in duck ponds for thousands of years has been uncovered by evolutionary biologists.

Faced with unwelcome advances from undesirable males wielding large, corkscrew-shaped penises, the females have gone on the defensive.

The solution – the result of millennia of evolution – arrived in the form of vaginas that spiral in the opposite direction, so thwarting uninvited males at a stroke.

Some female ducks possess genitalia of labyrinthine complexity, with kinks, dead ends and hairpin bends, according to a report in the ...

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