A team of researchers led by Ben Trumble at the University of Washington analysed testosterone levels before and after a series of football matches played by men from the Tsimane tribe in the Amazon rainforest. They discovered that the players experienced a 30 percent increase in testosterone immediately after the game, with testosterone levels remaining 15 percent higher an hour after the game. Similar increases have been shown in men living in the U.S. or other industrialized nations following sports competitions.
The researchers were interested in investigating the testosterone levels among the Tsimane because under normal conditions they have lower circulating levels of testosterone than men from industrialised societies. This is because of the increased susceptibility to infection associated with a high base level of testosterone; Tsimane men are more exposed to the dangers of infection than the average North American, so a lower base level of testosterone could offer them significant evolutionary advantages. However, the lower starting level of testosterone among Tsimane men led researchers to question whether they would still experience the same elevated levels of testosterone following competitive sport as men from industrialised societies do.
The study suggests that competition-linked bursts of testosterone are a fundamental aspect of human biology that persists even if it increases risk for sickness or infection. As for whether higher levels of the male hormone would offer a competitive advantage in sports, Trumble suspects that because U.S. men "are taller, and weigh more than Tsimane men, and tend to be exposed to fewer parasites and pathogens, they would probably have a competitive advantage regardless of circulating testosterone."
"What's interesting is that in spite of being in a more pathogenic environment, it's still important to raise testosterone for short-term bursts of energy and competition," said Michael Gurven, co-author and anthropology professor at the University of California Santa Barbara.