Primate species only have enough energy to grow either big testes or an impressive beard or mane, study claims

Correction

The results of the joint study by the University of Western Australia and the University of Zurich about the relationship between the size of sexual ornaments and testes in primates were misinterpreted and wrongly assumed to be about the difference between individual humans.

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A study by researchers from the University of Western Australia, has postulated that hairy men with long hair and beards have the smallest-sized testicles.

The Australian scientists examined the testicle sizes of more than 100 separate species of primates (including human beings) and learned that the testes vary in size and shape depending on the animal. The smallest were the size of peppercorns, while the largest were the size of tennis balls.

The researchers used testicle size as an indicator of dominance among mating males. But they noticed that there was a correlation between poorly-endowed males, who made an effort to look flamboyant and eye-catching instead, with vibrant hairstyles and longer fur. The same factors also appeared to be in play for homo sapiens.

Credit: 1621

Commenting on his study's findings (which were published in the journal Proceedings of the Royal Society B) primatologist and co-author Dr Cyril Grueter stated: "Not all of them can [mate]. So how do they succeed?  Well, next to simply fighting, they can produce so-called 'badges of status'; showy ornaments that help their bearers control access to females by intimidating other males. And if males cannot keep others off their females, they can win by producing a lot of sperm to swamp those from their rivals."

He added: "We found the same thing with ornamentation - some species sport flamboyant accoutrements such as beards, manes, capes and cheek flanges, and various shades of colour in their faces and fur. Others are pretty drab and look more like your Mr Average. This finding clearly shows that you can be well-adorned or well-endowed, but it's hard to be both."