Smaller testicles “suggest” an increased sense of paternal duty in men, say researchers from Emory University in the US. The evidence suggests that the smaller a man’s testicles, the more often he takes part in the care of his child. The study, which examined the relationship between fatherhood and testicle size, involved 70 men whose children were between the ages of one and two. Differences were also found in the brains of the participants corresponding to the size of their testicles while they were looking after their children. MRI analyzes show that fathers with smaller testicles show greater activity in the brain region associated with reward. During the interviews, they also showed greater activity in terms of fulfilling parental duties. NEWS_MORE_BOX Testicular size also plays a role in animal sex. Those with larger size are more likely to mate with more partners. In this regard, scientists are examining evolutionary theory regarding the investment of time and energy in mating, or “investing” it in raising children. The basic idea is that larger testicles suggest a greater commitment to procreation at the expense of taking care of it afterward. Although the relationship between the size of the testicles and the feeling of paternal duty has not yet been studied, experts believe that the answer lies in the level of the hormone testosterone in the male body. For now, what can be said for sure is that testosterone levels drop when men become fathers.