Researchers from Emory University have discovered that fathers with smaller testicles are more likely to be involved in caregiving activities like diaper changes, feeding, and nap time. Brains scans also show higher activity in their reward system. But the study is far from complete in its assessment.
It seems like a strange study to conduct, but the analysis was an effort to test the Life History Theory — the suggestion that an evolutionary trade-off exists between mating and parenting effort. The theory essentially asks, “Where is the bulk of a male’s time and energy better spent? Mating (i.e., sperm competition) or helping to rear offspring?” If affirmed, the Life History Theory could go a long way in explaining why some dads are more involved than others in the nurturing of their children.