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Even an hour after the game, testosterone was still 15 percent higher than under normal conditions for Tsimane men, who have a baseline testosterone level that is 33 percent lower than that of men living in the United States, report researchers in the Proceedings of the Royal Society B.

Tsimane men spend much of their time hunting, foraging, fishing, and clearing land by hand to grow crops. According to the study by anthropologists at UC Santa Barbara and the University of Washington, the Bolivian foragers-farmers do not show declines in testosterone as they age.

The lives of the Tsimane offer a glimpse of how humans survived before industrialization and modern amenities, says Michael Gurven.

“Our lifestyle is now an anomaly, a major departure from our species’ long-term existence as hunter-gatherers,” says Gurven, professor of anthropology at UC Santa Barbara and co-author of the paper. Gurven is also co-director of the Tsimane Health and Life History Project, a collaboration between UC Santa Barbara and the University of New Mexico.

“Maintaining high levels of testosterone compromises the immune system, so it makes sense to keep it low in environments where parasites and pathogens are rampant, as they are where the Tsimane live,” says Ben Trumble, a graduate student in anthropology at the University of Washington and the paper’s lead author.

That men living in the US have greater levels of circulating testosterone represents an “evolutionarily novel spike,” Trumble adds. The spike reflects how low levels of pathogens and parasites in the US and other industrialized countries allow men to maintain higher testosterone levels without risk of infection.

He also pointed out that while men in the US show a decline in testosterone as they age, and the drop serves as a sentinel for age-related disease, Tsimane men maintain a stable testosterone level across their lifespan, and show little incidence of obesity, heart disease, and other illnesses associated with older age.

Despite lower levels of circulating testosterone under normal conditions, the forager-farmers do have something in common with US men—short-term spikes of testosterone during competition.

The findings suggest competition-linked bursts of testosterone are a fundamental aspect of human biology that persists even if it increases risk of sickness or infection.

“What’s interesting is that in spite of being in a more pathogenic environment, it’s still important to raise testosterone for short-bursts of energy and competition,” Gurven says.

As to whether higher levels of the male hormone would offer a competitive advantage in sports, Trumble suspects that because US 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.”

The work was funded by the National Institute of Child Health & Development and the National Institute on Aging.

More news from UC Santa Barbara: www.ucsb.edu/news-topics

More news from the University of Washington: www.washington.edu/news/