Atlanta (CBS ATLANTA) — Men with small testicles are likely to be more nurturing and better fathers to their children.
A new study from Emory University finds that men who tend to be a loving parent also have smaller testicles. The research, released today in the Proceedings of the National Academy of Sciences, involved 70 men of varying ethnicities — most were Caucasian, five were Asian and 15 were African-American – with at least one child under two years old.
Prior studies have suggested that decreases in testosterone may suppress mating efforts, which potentially channels a man’s energy toward the care of infants and make these men more empathetic.
“Our data suggest that the biology of human males reflects a trade-off between mating and parenting effort,” says Emory anthropologist and study lead author James Rilling,
This study showed that men with smaller testes exhibited more nurturing activity in their brains when shown pictures of their children. Also, separate surveys from their respective female partners showed that these men were more involved in the upbringing of their children.
“I wouldn’t want to say that men with large testes are always bad fathers but our data show a tendency for them to be less involved in things like changing diapers, bathing children, preparing meals, taking them to the doctor and things like that,” said Rilling.
“The correlation is stronger between sperm count and sperm quality and testicle size,” Rilling explained. “Bigger size, better, healthier sperm.”
Larger sized testicles seemed to indicate men who were built for competition with other men to make women pregnant, but not so much to care for the child.
“Mothers definitely have more of an impact on child development, but fathers are also important and their role is understudied,” said Rilling.
The exact measurements of a “large” or “small” testicle were not made clear in the study.
“Our study is the first to investigate whether human anatomy and brain function explain this variance in parenting effort,” says Jennifer Mascaro, who led the study as a post-doctoral fellow in the Rilling lab. “Testes volume is more highly correlated with sperm count and quality than with testosterone levels.”
Both testosterone levels and testes size were inversely correlated with the amount of direct paternal caregiving reported by the parents in the study.