Article appeared on telegraph.co.uk
Winning a mate used to depend only on physical prowess and men with the strongest jawline and thickest skulls were better able to survive onslaughts from love rivals.
That meant that over time all men developed thicker bones in the jaws, around the eyes and on the forehead than women.
They also developed a greater proportion of muscle to fat than women and became taller than women, said the study,
Dr David Puts, whose findings are published in Evolution and Human Behaviour, said unlike many animal species men and women are similarly sized although men develop more muscle and women more fat.
Dr Puts, of Pennsylvania State University, said: "On average men are not all that much bigger than women, only about 15 percent larger. But the average guy is stronger than 99.9 percent of women."
Men are also far more aggressive than women, with about 30 percent in small-scale foraging communities dying violently. Dr Puts suggests while a deep voice has been considered an appealing trait to women, it actually signals dominance.
He said: "A deep voice makes men look dominant and older. A low voice's effect on dominance is many times greater than its effect on sexual attraction."
The main sticking point with human male competition compared to other species is men do not possess inherent weapons like antlers and claws. But they have always manufactured them instead including bows and arrows, spears and knives.
Dr Puts suggests species that live in three-dimensional space – birds and insects in the air or swimming creatures in the sea – tend not to compete for mates using physical competition because it would be very difficult for a male to defend females while fighting other males on all fronts.
Species that live on the ground or the sea floor have it easier because there are only two dimensions to defend. Some insects that live in tunnels or burrows exhibit the most intense competition because it is impossible for the other male to get to the females except through the defender.
Male competition is rare among birds, occurring to a greater degree among large terrestrial species. Tree-living primates also show less physical competition. Humans living in a two-dimensional environment would experience substantial physical competition for mates.
According to Dr Puts, humans and chimpanzees create male coalitions that are often strengthened by kinship. Coalitions can help males defend females from other males. But when external forces are absent, these same males can compete with each other for mates.
These ideas may seem to paint a rather bleak picture of human nature with men dishing it out among themselves for most of human evolution.
"Things are different for us now in many ways. It is heartening to think human behaviour is flexible enough that the right social institutions can increase equality and peace."
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