Just a whiff of an infant can quickly lower a father's testosterone levels and inhibit the likelihood its father will try any monkey business — in marmosets, at least.

The study done by the Wisconsin National Primate Research Center at UW-Madison focused on the small monkeys native to South America and the hormone levels of marmoset fathers.

Marmoset dads bear nearly as much of the responsibility of child rearing as the mothers, said Toni Ziegler, a staff scientist at the center. One of the important revelations of this study is the role testosterone plays in primate fatherhood.

Some studies show male testosterone directly affects aggression. Ziegler said because a marmoset baby's scent has the ability to lower testosterone, the fathers will most likely exhibit more care for their offspring.

"Essentially, this encourages the father to be there for the child," she said.

Ziegler said the research could lead to more profound studies on olfactory senses and their effect on primates and humans.

Kumar Guha, a father of two who lives in Madison, said he can relate to the findings because he experienced similar feelings when his children were born. He did not know whether his affection for his kids was due to decreased testosterone, but he said he felt "more soft."

"When you have kids, you don't feel the same need to be as aggressive," he said.

Ziegler said the study also found the monkey's testosterone level is flexible, meaning that while fathers tend to relax more around infants, they can still increase testosterone when needed in times of danger or mating. Ziegler noted female marmosets are often impregnated shortly after they give birth and mating requires an increase in testosterone.

The study was done with marmosets experienced in fatherhood. By isolating the dads from their families and the family's odor, Ziegler and company exposed the dads to an infant scent and a control scent. Ziegler said marmosets with no parenting experience showed indifference to the scents, but the experienced dads showed immediate results.

"Within 20 minutes, testosterone in experienced marmoset fathers began dropping significantly," Ziegler said. She said studies were not done on first-time marmoset dads.