The male proboscis monkey has a particularly large and long nose among primates.So far, the research team has found that nose size is related to vocal range, ensuring male physical strength and high fertility.The large nose is also a weapon that fascinates females, suggesting that they measure each other's strengths and avoid unnecessary conflicts over females.

　In general, in primates other than humans, males are stronger as their canines are larger than their noses, which is advantageous for victory in struggle and acquisition of females.The research team predicted that the proboscis monkey society is a multi-layered society in which Harlem-type herds gather, and because there is no territory in Harlem, females are in a fierce battle for competition, and stronger males have larger canines.

　However, it turned out that the stronger the male (larger physique), the smaller the canine tooth of the proboscis monkey.The males shook the branches with a large physique and indirectly fought against the competitors by making a cry with a big nose, which is a medal of a strong male, and avoided the fatal injury after the fierce struggle by the canines.

　Also, if the canines are too large, it will be disadvantageous for chewing food.Proboscis monkeys, which eat energy-inefficient leaves as their staple food, seem to have had an advantageous evolutionary strategy to overcome the competition between males by moderately developing their canines and eating food efficiently to increase their physique. ..

　The result of this research is an interesting phenomenon in which the trade-off (profit and loss) of traits has evolved due to the interaction between competition for sex (sex selection) and competition for life (natural selection). It is expected to lead to the elucidation of the mechanism of society and language generation.

Paper information:[Communications Biology] Large male proboscis monkeys have larger noses but smaller canines