"Hard guys" have less testosterone in their blood
US researchers have now discovered astonishing things: Really tough men have less testosterone in their blood. Although the life of the Tsimané in Bolivia is physically more demanding than that in the western world, men there have a much lower testosterone level. The researchers have now tracked down the cause.
Testosterone dampens the immune system
The people of the Tsimané in Bolivia lead a simple hunter-gatherer life. They hunt in the rainforests and do simple farming. Nevertheless, this people puzzles the anthropologists. Benjamin Trumble of the University of Washington at Seattle and his colleagues found that the male members of the tsimané had an average of a third less testosterone in their blood than US men. The online journal "Proceedings of the Royal Society B" reports.
The anthropologists were also surprised by this result. So far, men who do hard physical work every day have been assumed to have high testosterone levels. Ultimately, however, the researchers developed another much more conclusive thesis. "A high testosterone level dampens the immune system, so it makes sense to keep it low if you live in an area with lots of parasites and pathogens, like the Tsimané," explains Trumble that they could only afford because of the low risk of infection, and while men's testosterone levels in western industrialized countries decrease with age, the tsimané remains unchanged.
Testosterone kick in competitive situations provides energy But the Bolivian men have one thing in common with those from western industrialized countries. In competitive situations, the testosterone level in the blood increases briefly. To confirm this, the researchers let the Tsimané play soccer against each other. Testosterone levels were increased by 30 percent immediately after the competition. When measured again after an hour, it was still 15 percent above the average level.
In the sudden hormone kick in the competitive situation, the researchers saw a fundamental biological mechanism. They made the same observations in Western men. "Even in a highly pathogenic environment, it is important to raise testosterone levels in order to have energy in the short term and gain a competitive advantage," said Michael Gurven of the University of California, anthropologist and co-author of the study .
Since 2002, the people have been examined as part of the "Tsimane Life and Health History Project". Back in 2009, scientists around Gurven discovered that the tsimané developed almost no cardiovascular diseases.
Testosterone makes women more selfish At the beginning of the year, British scientists discovered that the male sex hormone testosterone made women more selfish and less cooperative. It was the first time that a hormone was discovered that caused restrictions in interpersonal cooperation.
While scientists have long known that some hormones such as oxytocin promote cooperative behavior in economic tasks, they now wanted to look for a hormone with the opposite effect. That is why Nicholas D. Wright and his colleagues studied the effects of testosterone on women. For the investigation, a pair of two women were shown two successive images on the computer, one of which was to be determined, on which a sought-after motif was hidden. If both women chose the same picture, the next pictures followed. If the test subjects opted for different images, they should discuss them with each other and agree on them. The women underwent the same attempt twice at intervals of one week. The women received ineffective placebos for one test and a dose of testosterone for the other. When evaluating the test results, the researchers found that without taking testosterone, the women could significantly improve their overall result through cooperative decisions. The researchers led by Nicholas D. Wright from the Institute of Neurology at University College London published their results in the online journal "Proceedings of the Royal Society B". (ag)
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Image: Karl-Heinz Laube / pixelio.de