Newborn babies may reduce male testosterone levels by around 60 percent, according to a University of Wisconsin study announced Wednesday.

Young marmosets, a type of monkey not genetically far from humans, release an odor that reduces the father’s testosterone level, calming him and allowing him to better aid the mother in parenting the child.

Toni Ziegler, staff scientist at the Wisconsin National Primate Research Center, led the research team. She believes that while most primates do not show this behavior, bi-parental primates do, including humans.

“There are some studies in humans, and it’s just on a general level,” Ziegler said. “But they’ve indicated that generally their testosterone levels are lower when they have young children than with [men who don’t have young children].”

Nancy Schultz-Darken, one of the researchers who worked with Ziegler, also believes the response could exist in humans as well as marmosets, and suggested that further research be done to explore that possibility.

“Scent is a very strong cue in a lot of primates and a lot of species,” Schultz-Darken said. “Probably more so in humans then we realize; of course, we cover that scent up a lot.”

Testosterone in both marmosets and humans increases sex drive and aggressiveness, and also promotes the growth of muscles.

All of those effects of testosterone decrease rapidly when a male marmoset is around his young, which Ziegler said is “very beneficial to the offspring.”

“What’s so surprising is that just the infants alone — without any other cues, without anything else — can have such a dramatic effect so quickly,” Ziegler said. “Within 30 minutes there’s a response.”

UW psychology professor Chuck Snowdon, a member of the research team, agreed with Ziegler that the rate at which hormones changed was staggering.

“It suggests the power of infant stimuli is great in terms of affecting a male’s behavior,” Snowdon said.

To conduct the study, Ziegler and her team isolated male marmosets from their families. Males with no offspring were also put in isolation.

Some of the fathers were given a control scent and some were given a scent from their infant’s genital area. Childless marmosets were given the same scents.

Blood tests consistently showed that fathers who were given a scent from their own infant experienced a dramatic and rapid decrease in testosterone levels.

The infant marmosets were around three-weeks-old when the study was conducted. Ziegler said the study did not conclude at what point — if ever — testosterone levels in male marmosets return to normal.

Ziegler and Schultz-Darken both believe testosterone levels can still go back up if a father feels the need to protect his family or habitat.

“I’m sure role changes significantly from a caregiver of infants to defending the family group,” Schultz-Darken said. “That’s the same in wolves I’m sure, as with many cooperative breeders.”

Previous studies have proven that male marmosets have a response to female scents, but this study from the WNPRC is the first to show any response to an infant scent.

The study was funded by a grant from the National Institutes of Health.