Studying the science of the paternal instinct in those animals could provide insights into humans.
In an online chat Thursday on the ScienceNOW Web site of the journal Science, researchers Kelly Lambert and Karen Bales talked about their research into those good animal fathers, which include prairie voles, California deer mice, titi monkeys and marmosets, the siamang ape and wolves.
Almost all of those species are monogamous, and that might be where the paternal change starts, said Bales, an associate professor of psychology at the University of California-Davis and the unit leader for Brain, Mind and Behavior at the California National Primate Research Center. Two important chemicals involved in bonding with a mate – oxytocin and vasopressin – are also involved in the parental response, she said.
“This is probably not an accident; they are ancient peptides that seem to have been co-opted for many social functions,” Bales said. “It is probable that the changes in the brain that occur with pair-bonding help to ‘set up’ the brain for being a dad, and perhaps vice versa. I wouldn’t say that there are any non-monogamous mammals that score really high in paternal contributions.”
There are genetic differences in humans in terms of response to those chemicals and one study found the variation in the ability to respond to vasopressin predicted marital quality of life, Bales said.
“So maybe it’s not a stretch to suggest that there could be genetic variation in humans that affects fathering as well,” she said.
In both animals and people, testosterone levels decline dramatically in fathers.
“The testosterone data is pretty consistent between animals and humans,” Bales said. “In general, testosterone tends to increase during times when males are establishing or defending their territory (the breeding season), and decrease again during infant care periods. This is usually attributed to the disadvantages of having high testosterone all the time, such as immunosuppression and aggression.”
In fact, it begins before the male even becomes a father, said Lambert, the chairwoman of psychology at Randolph-Macon College in Virginia.
“There has been research indicating that prolactin (a hormone that stimulates milk production) levels increase in human males around pregnant women as well as reductions in testosterone,” she said. A study published last month showed prolactin stayed higher in fathers than nonfathers.
There are actual changes in the rodent father’s brain that influence behavior, such as the response to pups or to anxiety, that could be possible in humans, Lambert said: “I would expect to see some similar trends: more anxiety circuits activated in the nonfathers and more areas involved in reward and nurturing responses in the experienced dads.”