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Fatherhood causes drop in testosterone - and may keep men loyal

New research suggests that men are “biologically wired” to remain for child-rearing – as testosterone levels drop after a partner gives birth.

Library photo posed by models.
Library photo posed by models.
Image: John Birdsall/John Birdsall/Press Association Images

MEN’S TESTOSTERONE LEVELS drop following the birth of their child – making them more likely to focus on family life and remain for child-rearing, according to the results of a new study.

Studies over the past number of years have shown that fathers tend to have lower levels of testosterone than their childless counterparts – however it wasn’t established whether this was because men with less testosterone were more likely to become fathers or if becoming a father lowered the body’s level of the hormone, according to the Los Angeles Times.

The research suggested that men with high levels of testosterone are more likely to secure a partner and father children, but that once a baby is born their levels of the hormone decrease. Men with a newborn child aged less than one month old and men involved in childcare showed especially low levels of testosterone, reports the BBC.

Lee Gettler, an anthropology doctoral student working on the new study, said: “It’s not the case that men with lower testosterone are simply more likely to become fathers. On the contrary, the men who started with high testosterone were more likely to become fathers, but once they did, their testosterone went down substantially”.

The lead investigator of the study, Christopher Kuzawa, said that humans were unusual among mammals because offspring depend on adults for feeding a protection for more than a decade – which meant there was more of a need for human fathers to remain to raise children, the Telegraph reports.

“Raising human offspring is such an effort that it is co-operative by necessity, and our study shows that human fathers are biologically wired to help with the job,” he said. “Fatherhood and the demands of having a newborn baby require many emotional, psychological and physical adjustments. Our study indicates that a man’s biology can change substantially to help meet those demands.”

The study took place in the Philippines and followed 624 men in their twenties for four-and-a-half years; it showed that a man’s testosterone levels drop by about a third following their partner giving birth.

Dr Allan Pacey, a male sexual health expert at Sheffield University, told the BBC that the observations of the study could make “some evolutionary sense if we accept the idea that men with lower testosterone levels are more likely to be monogamous with their partner and care for children”.

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He said: “Testosterone is the key hormone that defines male physiology. We know that levels correlate with a man’s sex drive, his risk–taking behaviour and social dominance. It has also been suggested that it may increase his attractiveness to women and help him find a mate”.

However Pacey urged caution about jumping to the conclusion that less testosterone meant a man was less likely to “stray”, saying that the study did not prove that.

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