A study from Emory University (USA) based on brain scans indicates thatmen with smaller testicular volume are more involved in paternal care. According to the authors inProceedings of the National Academy of Sciences(PNAS), the size of the gonads has to do with thetestosterone production, and this with the energy that the males invest in breeding.
“Previous studies had shown alink between strong father involvement and low testosterone levels“explains the anthropologist James Rilling, one of the authors of the work, in statements to the SINC agency.” Now we have found a relationship with the size of the testicles, “he adds.
Seventy biological parents between 21 and 43 years of age, with children of one and two years, participated in the work. Using functional magnetic resonance imaging (fMRI), the researchers, on the one hand, quantified the volume of the reproductive organs; and on the other, they monitored the brain activity of the parents while observing photographs of their offspring. In addition, the volunteers completed a survey on their degree of participation in childcare, with questions about common activities such as accompanying children to the doctor or care during the night. “The results indicate thatmen with smaller testiclesbecome more involved in child care and alsowhen viewing photos of their offspring they experience stronger stimuli in the brain circuits related to reward and motivation“, says the researcher.
Previous studies have shown that the size of the testicles is more strongly linked to the quantity and quality of sperm. The authors believe that the relationship between the size of the testes and the brain activity associated with caring for children suggests a balance between mating and rearing.
There is an evolutionary hypothesis according to whichall organisms have a finite amount of energy to devote to reproductive effort, which can be invested in parenting or mating. This theory suggests that both activities compete, so that men who spend more energy looking for mating opportunities are left with less strength available to care for their children, and vice versa. Data from other species suggest thatmating frequency is positively related to testicle size. And in the same vein, by lowering his testosterone levels, the male minimizes efforts to mate and channels them towards the attention of the offspring.
