Santa Barbara, Calif. As part of an isolated indigenous group in central Bolivia, Tsimane men spend much of their time hunting, foraging, fishing, and clearing land by hand to grow crops. Their ability to maintain the physical activity required to survive each day might imply they have higher than average male testosterone levels.
Anthropologists at UC Santa Barbara and the University of Washington have found, however, that the baseline testosterone level of Tsimane men is 33 percent lower than that of men living in the United States, where life is physically less demanding. Also, in contrast to men in the U.S., the Bolivian foragers-farmers do not show declines in testosterone as they age. The researchers' findings appear today in the Proceedings of the Royal Society B.
According to Michael Gurven, the lives of the Tsimane offer a glimpse of how humans survived before industrialization and modern amenities. "Our lifestyle is now an anomaly, a major departure from our species' long-term existence as hunter-gatherers," said Gurven, professor of anthropology at UCSB and co-author of the paper. Gurven is also co-director of the Tsimane Health and Life History Project, a collaboration between UCSB 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," said Ben Trumble, a graduate student in anthropology at the University of Washington, and the paper's lead author.
That men living in the U.S. have greater levels of circulating testosterone represents an "evolutionarily novel spike," Trumble continued. The spike reflects how low levels of pathogens and parasites in the U.S. and other industrialized countries allow men to maintain higher testosterone levels without risk of infection. He also pointed out that while men in the U.S. show a decline in
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University of California - Santa Barbara