According to a HealthDay report, researchers are hoping to discover if the difference between fathers who are highly involved with child rearing and fathers who aren't is a matter of brain function or anatomy.
More specifically, they've been exploring a link between the size of a man's testicles and the level of testosterone, and parenting style.
The study, which included 70 fathers of children aged 1 to 2, used blood tests to measure testosterone, and interviews with fathers and mothers separately asking how often the man fed, bathed, prepared food for children or took them to appointments. Researchers also used an MRI brain scan to monitor the fathers' brain activity while looking at pictures of children. MRI technology was also used to measure the size of the men's testicles.
What they found suggested that the men with lower testosterone and smaller testes were more engaged caregivers. Testes volume was also correlated with the the men's increased neural response, specifically in the reward center of the brain, to viewing photos of their own offspring.
These results don't take into account that the very act of being involved caregivers may have an effect on testosterone levels and testicle size.