22 July 2009
by Linda Geddes
Magazine issue 2718
YOU may be tempted to think men are becoming an optional extra in the mating game, but biochemical evidence in mice and people suggests that fathers may play a key role in the rearing of offspring.
Previous studies have hinted at the importance of fathers in child-rearing. Some have shown that girls reach puberty younger, become sexually active earlier and are more likely to get pregnant in their teens if their father was absent when they were young. Others have suggested that the sons of absent fathers display lower intimacy and self-esteem.
To investigate the biological basis of such differences, Gabriella Gobbi at McGill University Health Centre in Montreal, Canada, and colleagues turned to "California mice", which, like people, are monogamous and tend to rear their offspring together.
The researchers removed the fathers but not the mothers from some of the mouse pups, from three days after birth until they were weaned at 30 to 40 days old. Then they looked at the activity of brain cells in the prefrontal cortex, an area involved in social interaction and expression of personality, in response to the hormone oxytocin and other neurotransmitters, including serotonin, dopamine and NMDA.
Cells in pups deprived of fathers had a blunted response to oxytocin - the "cuddle chemical", which is normally released during social interactions and pair bonding. They also had an increased response to NMDA, which is involved in memory.
The fatherless mice were also less interested in engaging with other mice. "Usually if you put two animals in the same cage they investigate and touch each other, but when we put two animals deprived of a father together they ignored each other," says Gobbi. Her colleague Francis Bambico presented the work at the World Congress of Biological Psychiatry in Paris, France, in early July.
Whether there are also biochemical differences between the brains of human children with present and absent fathers is not known. Michael Meaney, who studies the effects of maternal care at McGill, advises caution when applying the mouse results to people. In California mice it is the father that licks the pups most, he says. Since grooming affects pup development, it could be a lack of this, rather than anything else specific to the father, causing the brain changes.
There is, however, evidence that when men become fathers they undergo biochemical changes that affect their behaviour. Ruth Feldman of Bar-Ilan University in Ramat-Gan, Israel, visited 80 couples shortly after childbirth and again after six months, and found that the transition to parenthood was associated with increased oxytocin not only in mothers but also in fathers, compared with single, childless people.
Oxytocin levels in the parents also had different effects in each sex. Mothers with highest levels of the hormone engaged in more gazing at the infant, affectionate touching and speaking in a sing-song voice. Fathers with higher oxytocin played more with their child, who displayed more attachment to them than did kids whose fathers had lower oxytocin.
Higher oxytocin had different effects in each sex. Fathers engaged in more play with their child
"Fathers and mothers contribute in a very specific and different way" to infants' social and emotional development, says Feldman, who presented the results at a Society for Research in Child Development meeting in Denver, Colorado, in April. She says fathers may be "biologically programmed" to help raise children.