Father and son
Size of a man’s reproductive organ can predict his role and involvement as a father.reuters

The size of a man's reproductive organ can predict his role as a father. A new study found that men with smaller testes were more actively involved in their children's upbringing than those with a bigger organ .

For the study, researchers from the Emory University included 70 biological parents and their children. The study involved children aged between one and two. Through interviews, researchers collected information about the father's parenting skills, including bathing, feeding the child, changing diapers and taking care of the child when he/she is ill.

Researchers measured and recorded the male participants' testosterone levels. Using functional magnetic resonance imaging (fMRI), researchers analyzed brain activity of the participants in different situations by looking at their child's photo. They repeated the experiment with similar photos of an unknown child and an unknown adult.

While analysing the link between physical features of men and their involvement as a father, researchers found that fathers with smaller testicular volume showed better activity in the brain area related to reward and parental motivation - the ventral tegmental area (VTA) while viewing their child's photos.

Levels of testosterone, a steroid hormone in the human body, plays a major role in determining the father's efficiency in responding and fulfilling their children's needs. Previous research has shown that testosterone levels of men decreased when they become fathers and the reduced testosterone levels helped improve a father's parental involvement. Higher levels of the hormone have been associated with divorce and polygamy.

"We're assuming that testes size drives how involved the fathers are," Emory anthropologist James Rilling, said in a news release, later adding that "it could also be that when men become more involved as caregivers, their testes shrink. Environmental influences can change biology. We know, for instance, that testosterone levels go down when men become involved fathers."

The findings, reported in the journal PNAS, support a previous study published in the journal PLOS ONE in September 2012. The study found that fathers who slept close to their children had low testosterone levels, leading to a positive impact on their role as a father.

Previous research has shown that positive interaction of the father helped healthy growth of the child. Engaging with children positively in the early postnatal period decreased behavior problems in children and helped build the quality of persistence in children, which helps them achieve success in life.