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Manly and Mushy

Nothing melts manly into mushy like fatherhood. Now a study of
marmoset monkeys reveals how the mere scent of his baby turns dad from protector to parent, by ratcheting down levels of the male hormone testosterone.

"We have found when they are smelling the infant scent they have hormonal changes which may make them more maternal-like, more interested in bonding with an infant, whereas when their testosterone goes up, they may be more ready to, say, defend their family," says lead researcher Toni Ziegler, a senior scientist at the Wisconsin National Primate Research Center at the University of Wisconsin-Madison.

"Testosterone is known for increasing muscle mass in males, and it also has behavioral effects, such as a tendency to make one more aggressive, which might be important if you need to protect your family," Ziegler explains. "It’s also very much involved in mating behavior, and increased testosterone occurs when males are mating, or interested in, or interacting with a female that may be ovulating."

"You don’t normally think of someone that’s providing a lot of care for an infant to be aggressive or be interested in mating," she adds. "So this way, a father can respond with lower testosterone at a time when he’s interacting with his infant, but at times when he needs to be more protective of the family his testosterone is able to change and respond to the environment."

Ziegler and her colleagues study marmoset monkeys because they are similar to human families, with both parents involved in childcare.

"That’s why we’re so interested in studying them," she says. "They make such a great model for humans because these marmosets actually live in families where the male and the female both take care of the infants. As infants are born and they get older, they also learn how to take care of the infants by taking care of their younger siblings. So it’s a nice family environment and everyone is involved in infant care." That’s important because female marmosets usually have twins, she says. "These twins are relatively big in relationship to the mother’s size when they’re born, so she needs a lot of help in caring for these infants– it’s a high energetic demand."

Fast and Flexible

The researchers placed either infant scents or a background scent onto wooden dowels and let either fathers or single males smell them for ten minutes. As they wrote in "Biology Letters," they allowed another ten minutes for the males’ brains to process the scents, then measured their testosterone levels. While the scent of their own infant dampened dads’ testosterone, single males showed no significant change.

Ziegler is impressed at the power of baby’s scent to trigger this physiological response in their father. She and her colleagues have been using MRI imaging to learn how marmosets’ brains respond to different environmental stimuli, including olfactory cues. The need for reliable odors to use in this research is what led her to wonder about the effects of infant scents.

She’s also impressed at the speed of the response. "It happened within 20 minutes, so it’s a very rapid change– showing the brain in the fathers is actually processing this (the smell) very quickly and then the hormone system is responding to that," she says.

Ziegler says finding that the testosterone system has evolved to be so flexible highlights the importance of dad’s bond to his offspring.

"When you have social systems where the family is all-important, I think these bonds really need to be there. And that’s sort of the message for humans," she says.

So dads, now you know why it’s so easy for your kid to make a monkey out of you.

This research was published online in Biology Letters, August 26, 2008, and funded by the National Institutes of Health.

Elsewhere on the Web:
Wisconsin National Primate Research Center
Research on Marmoset Paternity Leads to Genetic Discovery—University of Nebraska, Lincoln news release

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Responses

1. rypitch says:
   

   October 28th, 2008 at 1:42 pm (#)

   Very interesting reaction. I wonder what effect the child's scent has on the mother?

2. Lois Ann McCollum says:
   

   December 12th, 2010 at 9:40 am (#)

   Hi Toni, Uncle Oscar tried to send you an email the other day and it wouldn’t go thru. Have you changed it?
   Love, Lois Ann and Oscar

3. Puja And Homam says:
   

   May 9th, 2013 at 12:48 am (#)

   When I initially left a comment I seem to have clicked on the -Notify me
   when new comments are added- checkbox and now each time a comment is added I
   receive 4 emails with the same comment. Perhaps there is a way you can remove me from that service?
   Thanks a lot!

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