The expression, “He’s got balls” doesn’t count when it comes to fatherhood.
Testicle size ‘link to father role’
A link between the size of a father’s testicles and how active he is in bringing up his children has been suggested by scientists.
Researchers at Emory University, US, said those with smaller testicles were more likely to be involved with nappy changing, feeding and bath time.
They also found differences in brain scans of fathers looking at images of their child, linked to testicle size.
But other factors, such as cultural expectations, also played a role.
Levels of promiscuity and testicle size are strongly linked in animals, those with the largest pair tending to mate with more partners.
The researchers were investigating an evolutionary theory about trade-offs between investing time and effort in mating or putting that energy into raising children. The idea being that larger testicles would suggest greater commitment to creating more children over raising them.
The study, in Proceedings of the National Academy of Science, looked at the relationship between testicle size and fatherhood in 70 men who had children between the ages of one and two.
The team at Emory University in Atlanta performed brain scans while the men were shown pictures of their children.
It showed those with smaller testicles tended to have a greater response in the reward area of the brain than those with a larger size.
MRI scans showed a three-fold difference between the volumes of the smallest and largest testicles in the group.
Those at the smaller end of the spectrum were also more likely, according to interviews with the man and the mother, to be more active in parenting duties.
How promiscuous baboon fathers help young to succeed
The offspring of promiscuous baboon males are more successful when they have contact with their father, scientists have found.
A study by a team of European researchers has documented increased feeding success when foraging with adult male baboons.
Paternity analyses allowed the scientists to determine whether the males were, in fact, the fathers.
The findings are published in the journal Behavioural Ecology.
Paternal care is uncommon in promiscuous mammals where it is not obvious which male actually is the father.
Lead researcher, Dr Elise Huchard of the University of Cambridge’s Department of Zoology, told BBC Nature: “Caring for offspring can be costly in terms of time and energy for the parents.”
She explained that parental care increases the chances of offspring survival, as well as improving an individual’s survival and reproductive performance later on in life.
“Paternal care is usually observed in species where paternity certainty is high, [such as] in monogamous species,” according to Dr Huchard.
So when research suggested that juveniles benefitted from paternal input in promiscuous baboon troops, Dr Huchard and colleagues decided to perform field research on two troops of chacma baboons (Papio ursinus) in Tsaobis Leopard Park, central Namibia.
The baboons’ habitat includes closed woodlands and open desert.
Juveniles ‘maintain relationships’
Previously, little was known about the role of chacma baboon fathers in their offspring’s survival, other than protecting against infanticide in early life.
Infanticide by adult males is very frequent in chacma baboons, killing up to 30% of juveniles in some baboon populations.
Alternative benefits of paternal behaviour, such as aiding foraging success, had never been investigated.
But research showed that juveniles whose father is present grow and mature more quickly in promiscuous baboon troops.
The scientists used a combination of paternity analyses and natural observations of adult male and juvenile baboons.
Dr Huchard explained: “We carried out many focal observations on each juvenile. One focal observation consists of spending one full hour following a given juvenile and recording everything that he does – like sampling a little slice of his life.”
The researchers recorded what and how much each juvenile ate at given tree or plant, together with which adult males were around, and the proximity of the baboons.
Juvenile baboons are difficult to tell apart in the field as they look very similar to each other.
Dr Huchard’s team had managed to mark every single baboon earlier in the season, which made each of them recognisable.
“This allowed us to conduct these detailed observations and to gain unique insights into the daily life of these really young baboons, who are otherwise often ignored by baboon field studies.”
The field results were corroborated by DNA-based paternity analysis tests in the laboratory.
The study proved that juveniles joined their father most often at feeding time, and foraged more successfully with their fathers than without them. They also associated more with their fathers than with other males.
Observations also showed that it was the juveniles, not the fathers, that maintained these associations by following their father.
The study found that juveniles joined their fathers more often when their mother was absent and when another adult male was nearby, suggesting that fathers may provide protection against potential dangers.
Dr Huchard was originally involved in other areas of research, but was intrigued by behaviours that she observed in the baboon troops.
“I was puzzled by seeing these big males being followed everywhere by their ‘kindergarten’ as well as being incredibly patient with the small baboons. I wanted to understand what these long lasting bonds meant to both adult males and juveniles.
“Previous research in olive baboons had suggested that males could care for unrelated infants as a courtship strategy, in order to seduce the mother.
“So it was exciting to find that in this population, males actually care for their own offspring, which suggests that they are able to discriminate their own offspring and that such bonds do represent paternal care.”
Dr Huchard explained why these findings have great relevance for future research: “It’s now an important goal for future research to identify why some fathers care more than some others, or why some juveniles develop stronger bonds with their father.”
“Understanding these patterns in baboons may help understanding the evolutionary origins of individual variations in paternal behaviour in humans.”