It was brawn over beauty in human mating competition, anthropologist says

"There is sexual competition in many species, including humans," said David A. Puts, assistant professor of biological anthropology.

Many researchers have considered mate choice the main operator in human sexual selection. They thought that people's mating success was mainly determined by attractiveness; but for men, it appears that physical competition among males was more important. Puts sees humans as similar to many of the apes in using male competition to determine access to mates, the winning male choosing the women of his dreams. He reports his findings in the current issue of Evolution and Human Behavior.

"On average men are not all that much bigger than women, only about 15 percent larger," said Puts. "But, the average guy is stronger than 99.9 percent of women."

The problem is that men and women do not appear sexually dimorphic -- different sexes having radically different sizes and weights. But Puts notes that women tend to store more body fat, while men have 60 percent more muscle mass than women.

Other traits indicate physical prowess was the major force in human mate competition through history. Men are far more aggressive than women, and approximately 30 percent of men in small-scale foraging communities die violently. Puts suggests that while a deep voice has been considered an appealing trait to women, it actually signals dominance.

"A deep voice makes men look dominant and older," said Puts. "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 that male humans do not possess inherent weapons.

"Other animals have antlers or long canines and claws," said Puts. "Why don't we have them?"

According to Puts, men do have weapons. They make them. Bows and arrows, spears, knives -- men have always manufactured weapons.

Other male traits also seem to imply competition. Males have thicker jawbones, which may have come from men hitting each other and the thickest-boned men surviving. Competition may explain why males have more robust skulls and brow ridges than women.

Another argument for male competition focuses on the environment. Puts suggests that 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 Puts, humans and chimpanzees create male coalitions that are often strengthened by kinship. Coalitions can help males defend females from other males. However, 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 duking it out among themselves for most of human evolution.

"Things are different for us now in many ways," said Puts. "It's heartening to think that human behavior is flexible enough that the right social institutions can increase equality and peace."