A Syracuse University research team has discovered something quite remarkable, if not immediately useful in everyday life*: bats belonging to species where the females are promiscuous have bigger testicles than those in species where the girls are more family-oriented.
There is, however, a price to pay: the bigger your 'nads, the smaller your brains, according to team leading biologist Scott Pitnick, who quipped: "It turns out size does matter."
Pitnick's research, which according to AP features in last December's Proceedings of the Royal Society: Biological Science, concludes that males in some species "make an evolutionary trade-off between intelligence and sexual prowess", as bat-mating expert David Hoskens of Exeter Uni explained.
Pitnick's team examined 334 bat species, finding that in those with monogamous females, males had testes ranging from 0.11 per cent of their body weight to 1.4 per cent. In contrast, in species with promiscuous females, the testicles ranged from 0.6 per cent to 8.5 per cent of the males' mass. Rafinesque's big-eared bat was apparently the species with the league-topping testes.
"Bats invest an enormous amount in testis, and the investment has to come from somewhere. There are no free lunches," Hoskens illuminated. The reason your bat might be obliged to invest so much in the trouser department is simple. "If female bats mate with more than one male, a sperm competition begins. The male who ejaculates the greatest number of sperm wins the game, and hence many bats have evolved outrageously big testes."
Naturally, if you've put all your energy into record-breaking nuts because the girls on your block are putting it about, you might have an "adaptive advantage", but there simply is not enough energy left to invest in a bigger brain.
Bat chaps are not the only males who walk bow-legged with a vacant expression on their faces - chimpanzees too are promiscuous and their cojones are much bigger than those of gorillas, where one bloke controls several females without fear of competition.
* Oh, alright then - it's a real dinner party show stopper: "Yes, it's true: the poor thing had bollocks like bowling balls but was as thick as ten short planks nailed together..."
And thanks to reader John Emery for the testicular heads-up.