A study has suggested that new fathers may be less inclined towards having sex.
Lee Gettler, of the University of Notre Dame in Indiana, tracked the lives and hormones of 433 young men from the Philippine islands and found that the most testosterone-fuelled men were also the most likely to become fathers.
But after having a baby their levels of the male sex hormone dropped along with the amount of sex they had,Daily Mail reported.
Gettler also found an increase in the hormone prolactin, which is normally associated with breastfeeding, particularly among men with the most hands-on approach to parenting.
It is thought the hormonal changes make a man more responsive to the needs of his child.
"Mothers undergo substantial biological change with pregnancy and birth, yet there has been a tendency to think of the father as kind of inertly along for the ride," Gettler told the American Association for the Advancement of Science's annual conference.
But it is not just mothers who respond to the demands of parenthood.
"I think evolution has shaped male physiology to help men invest in their children and provide good care for them."
"The drop in libido could well be nature's way of stopping the new father from straying," he added. But it is not for ever -- as hormone levels return to normal within a year or two.