No one would accuse the men of the Tsimane tribe of Bolivia of being anything less than manly, given their hunter-gatherer lifestyle. But new research suggests that Tsimane tribesmen have a third less baseline testosterone than their more sedentary American counterparts.
The study highlights the gap between the popular conception of testosterone as a chemical jolt of masculinity and the actual complexities of the hormone. In fact, having high baseline levels of testosterone can be a handicap for men.
"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," study researcher Ben Trumble, an anthropology graduate student at the University of Washington, said in a statement.
Trumble and his colleagues measured salivary testosterone in 88 16- to 59-year-old Tsimane men 15 minutes before a multi-village soccer tournament. After these men played in the tournament, the researchers measured their salivary testosterone again 10 minutes later and then an hour after the game.
They found that compared with age-matched American men and controlling for body size, baseline testosterone levels among the Tsimane are low: 182.9 picograms per milliliter for Tsimane men versus 266.8 picograms per milliliter for U.S. men. Like men the world over, however, the Tsimane soccer players got a testosterone boost from competition. Ten minutes after the game, their salivary testosterone was 30 percent higher than the pre-game measurement. An hour later, it was still 15.5 percent higher than before the game.
Studies of men in industrialized countries suggest they get a similarly sized boost from competition at about 37 percent, the researchers report today (March 27) in the journal Proceedings of the Royal Society B.
The study highlights the oddity of the industrialized man, study co-author and University of California Santa Barbara anthropologist Michael Gurven said in a statement.
"Our lifestyle now is an anomaly, a major departure from our species' long-term existence as hunter-gatherers," Gurven said.
This lifestyle change could have important health effects, the researchers found. Unlike American men, the Tsimane did not see a decline in baseline testosterone with age. In the U.S., drops in testosterone correlate with the onset of age-related disorders such as heart disease rarely seen in the very active Tsimane, Trumble said.