It’s been said that changes in male investment in mating strategies, mate seeking behaviour and parenting effort might be associated with changes in testosterone levels. But scientists studying the Ariaal tribe (subsistence pastoralists living in northern Kenya) found that they experience a decline in levels of the male hormone only after they get married, according to research published in Current Anthropology.

The Ariaal have an “aloof” marital system; whereby, apart from sex, husbands and wives have very little to do with each other, and the men are only minimally involved in childcare. Ariaal men remain single “warriors” until they are about 30 years old, at which time they marry one or more women.

The researchers measured testosterone in 205 Ariaal men, aged 20 and over; and (contrary to prediction) found that those with one wife had lower levels of the hormone than unmarried men, and polygynously married men had lower levels still.

Peter B. Gray (University of Nevada) and colleagues said:

Testosterone levels are lower among married men probably because they are investing less in mating effort, or to put it another way, they no longer have to compete for mates.

The finding provides both a social and evolutionary explanation for the decrease in testosterone, rather than an age-related one; and so, whilst variation in testosterone may still be associated with mating effort in young Ariaal men, political networks and wealth may be better predictors of marital status in older men.

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Posted by Jonathan in Anthropology, Sociobiology

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