Married men, no matter how aloof or hands-off they are with children, have lower testosterone levels than single men, a study has found.

The study, which appears in the October issue of Current Anthropology, investigated the links between male testosterone levels and marital status among modern-day pastoralists in northern Kenya, of whom less than 1.5 percent consider their wives a source of emotional support.

The Ariaal males serve as herd boys until they reach puberty, at which point they are initiated, become warriors and accumulate livestock. They do not marry and have children until around 30 and, the researchers suggest, value social bonds with male peers more than bonds with spouses or family.

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"These findings add to the cross-cultural scope of published data on the topic of human pair bonding, parenting and testosterone," wrote researchers Peter B. Gray, of the University of Nevada, Las Vegas, Peter T. Ellison, of Harvard University, and Benjamin C. Campbell, of Boston University.

"While a number of North American studies have shown lower testosterone levels among monogamously married men compared with their single counterparts, no study outside North America had observed this."

The researchers measured testosterone in morning and afternoon saliva samples of more than 200 Ariaal men over the age of 20. They found that monogamously married men had lower testosterone levels than unmarried men in both the morning and afternoon.

Contrary to expectations, polygynous married men had even lower levels of testosterone than monogamous married men.

"These results lend further support to arguments that male testosterone levels reflect, in part, variation in male mating effort," the researchers wrote. "Contrary to earlier findings, polygynously married men did not show higher testosterone levels. In fact, follow-up analyses among Ariaal men age 40 and older revealed lower testosterone levels among polygynously married men compared with monogamously married men."

The researchers suggest that this may be due to the fact that it is older men — who typically have lower testosterone levels — who have the social status and wealth required to obtain more than one wife.