Could there be a link between the size of a father's testicles and how active he is in bringing up his children?
A new study reported by the BBC has found that men with smaller
testicles were more likely to be involved with nappy changing, feeding
and bath time.
Researchers at Emory University in the States studied 70 men who had children between the ages of one and two. The research is based on evolutionary theory
about trade-offs between investing time and effort in mating, or putting
that energy into raising children. Larger testicles, linked to the hormone testosterone, are thought to suggest greater commitment to creating more children over raising
them. In the animal kingdom, it's the males with the biggest nuts who tend to mate with the most partners.
In the study, men at the smaller end of the spectrum were more
likely, according to interviews with the man and the mother, to be more
active in parenting duties. Presumably those with balls like spacehoppers just shoot their load and are barely seen for dust.
The researchers also found differences in brain scans of fathers looking at images of their child, linked to testicle size. Those with smaller testicles tended to have a
greater response in the reward area of the brain.
For me, one of the most interesting aspects is that MRI scans showed a three-fold difference between the volumes of the smallest and largest testicles in the group. Three fold!! And if you're a Dad, they could be shrinking: researcher Dr Rilling said "We know that testosterone levels go down when men become involved fathers." Further studies, analysing the size before and after becoming a father, are needed.
I suspect this is just the latest study in a long line of research comparing markers of testosterone with personality and behaviour. For example, I would have thought there has been research on 'digit ratio' and fatherhood. There are likely to be lots of other factors involved, and it's hard to imagine the study having much practical impact, other than lots of men today comparing the size of their bollocks while swapping stories about how involved they are with their kids. As Dr James Rilling told the BBC: "It
tells us some men are more naturally inclined to care-giving than
others, but I don't think that excuses other men. It just might require
more effort for some than others."