Recent research explains the metamorphosis of men from macho muscle machines to cuddly bears around babies!
A study has shown that levels of oxytocin, the 'cuddle chemical' released into the blood during labour, also rise in new fathers.
Not just that, their bodies see a sudden surge in prolactin, a hormone more commonly linked to milk production in new mothers.
"This seems to be evolution's way of helping men turn into good parents as soon as they have a baby," The Daily Mail quoted Ruth Feldman as saying.
"These hormones seem to have a powerful role in helping men bond with their newly-born children," she added.
Feldman, of the Bar-Ilan University in Israel, studied levels of the two hormones in new fathers in the six months after the arrival of their first.
It is thought that in the months after becoming a father, the hormones rewire men's brains, making them more empathic, playful and cuddly.
It is also possible that as the father's daily encounters with his infant increase, the prolactin and oxytocin systems reorganise and create new connections.
Taking a different view, Dr Michael Craig, of the Institute of Psychiatry, King's College London, said, "Oxytocin is also known to rise in response to elevated levels of stress, so this could also be part of the explanation."
The study is published in the journal Hormones and Behavior.