Males with flamboyant physical ornaments – such as beards and long hairs have smaller testicles, according to a newly released study.
The finding comes from a study that looked at testicle size of more than 100 primate species – including humans – and found gonads vary dramatically among different animals.
The smallest testicles were found to be the size of peppercorns while the largest was comparable to that of a tennis ball’s diameter.
Researchers explain that poorly endowed males commit all their energy into attracting mates using beards and long hair and have none left to invest in their genitalia.
Researchers chose to study primate testicle size as it varies so widely in different populations.
Primatologist and study co-author Dr Cyril Grueter, from the University of Western Australia, said male primates live in highly competitive environments.
Dr Grueter said primate testicle size varies enormously.
‘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,’ he said.
‘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,’ Dr Grueter said.
Researchers explain that poorly endowed males commit all their energy into attracting mates using beards and long hair and then have none left to invest in their genitalia.
One of the reasons, the researchers suspect, is that trying to do both just takes too much energy.
He explains that all the males are striving for the same thing – to father offspring.
‘But not all of them can have what they want,’ Dr Grueter said. ‘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.’