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Fathers with small testicles more likely to be involved in child care because they have lower testosterone levels.
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Decreases in testosterone may suppress mating efforts, channeling a man’s energy toward child care.
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Testes volume is associated with sperm production and testosterone levels.
Men with small testicles are better parents, new research suggests.
Researchers found that fathers with smaller testicles are more likely to be involved in child care.
Previous studies have suggested that decreases in testosterone may suppress mating efforts, potentially channeling a man’s energy toward the care of infants.
This ties in with an evolutionary hypothesis called Life History Theory which holds that mating and parenting compete for the limited energy animals expend on reproduction, reports the Proceedings of the National Academy of Sciences Online.
Dr James Rilling, of Atlanta’s Emory University, decided to investigate the link between testes size and parenting among men.
Testes volume is associated with sperm production and testosterone levels.
His team studied 70 fathers aged between 21 and 43, all with young children.
Their testes were measured and MRI scanning was used to monitor the activity in a region of the brain implicated in parental motivation, while the men viewed photographs of their own child, a stranger’s child, and an adult stranger.
The specific measurements of a ‘large’ or ‘small’ testicle were not made clear in the study, however.
The men’s partners answered a parenting questionnaire that questioned the fathers’ involvement in tasks such as taking children to health care visits and attending to children at night.
The researchers found that fathers’ testes size was negatively tied to nurturing-related brain activity triggered while they viewed pictures of their own child.
In particular, fathers who were more responsive than others to their child’s emotional faces tended to have smaller testes and be more involved in infant care.
Dr Rilling said: ‘The link between testes size and parenting-related brain activity suggests a trade-off between mating and parenting.’
