The proboscis monkeys of Malaysia – perhaps not the best looking our distant primate cousins – is famed for its strange shoe-shaped nose. But what is the point of wielding this impractical nose on the front of your face? Well, according to a new study, it's almost certainly to do with sex.
New research from Cardiff University in the UK, the Danau Girang Field Centre in Mayalysia, Kyoto University in Japan has found a clear link between the nose size of the male monkeys and the number of females in their harems, suggesting that big-nosed males have more sex than the smaller-nosed counterparts. Not only that, a bigger nose also seems to mean bigger testicles.
Their study was research published in the journal Science Advances.
"Although the unique nature of the 'odd-nosed' proboscis monkey has long been admired as an extremely attractive visual feature by biologists, explanations for its evolution have so far been gleaned more from folklore than from science,” Dr Sen Nathan, Assistant Director of Sabah Wildlife Department at Cardiff University, said in a statement.
To reach this conclusion, researchers studied the behavior and anatomy of captive and free-ranging proboscis monkeys, searching for correlations between body mass, facial characteristics, testicular volume, vocalizations, and the number of harem females.
“In addition to finding that enlarged male noses serve as advertisements to females in mate selection, we also found that males with larger noses also tended to have larger body mass and testis,” noted Dr Ikki Matsuda, Chubu University and Kyoto University in Japan. “This suggests that nose enlargement is a reliable predictor of social dominance and high sperm count.”
Dr Nathan added: “We also observed that nasal enlargement modified the resonance properties of male vocalizations, which probably encode male quality. Our results, therefore, indicate that the audiovisual contributions of enlarged male noses serve as advertisements to females in their mate selection.”
This phenomenon is known as sexual selection and can be found throughout the animal kingdom. It’s the same idea as a male peacock showing off its pretty feathers to impress a female. Although the features might decrease the male's chances of survival, it can increase its chances of reproductive success by “advertising” its sexual prowess to a would-be mate. For the proboscis monkey, a chubby snout means is an audiovisual cue towards the females to show who is the dominant male and therefore who is worth reproducing with.