A study published in the journal PNAS found that smaller testicle size in men appears to be liked to greater involvement in child-rearing.
Study researchers from Georgia found and recruited male participants all with children under the age of 2 years old via fliers and Facebook advertisements. They then measured each man's testosterone levels and testes volume. They also performed brain scans while they were shown pictures of their own children's faces and those of strangers. Researchers also included mothers by surveying them on the father's level of parental involvement. Researchers, in the study notes, say that the intention of the study was to determine whether biological factors accounted for absentee fathers.
They wrote, "In modern Western societies, some fathers choose not to invest in their children. Why do some men make this choice? Life History Theory offers an explanation for variation in parental investment by positing a trade-off between mating and parenting effort, which may explain some of the observed variance in human fathers' parenting behavior." And though previous research suggests that decreased levels of testosterone suppresses male parenting efforts and also affect male parenting. However, this study proves that smaller testes may lead the way for better fathers.
Lead researcher Jennifer Mascaro, an anthropologist, said, "Fathers' testicular volume and testosterone levels were inversely related to parental investment and testes volume was inversely correlated with nurturing-related brain activity when viewing pictures of their own child." Translation: men with lower testicular volume and testosterone levels were determined to be better fathers.
"Collectively," the authors write, "these data provide the most direct support to date that the biology of human males reflects a trade-off between mating and parenting effort."
Do you think testes size affects your partner's parenting?