Yale University neuroscientists Ruth Feldman found this out after comparing the oxytocin levels in 80 couples when they first became parents. Feldman believes the increase in the level of oxytocin, which encourages muscular contractions in women during birth, in men was caused by his close contact with his newborn.

In another set of experiments that study the levels of the two hormones in 43 fathers during a six-month period after their wives delivered their first child, Feldman and his colleagues found a strong correlation of between the levels of their hormones and how good they are at playing and communicating with their babies.

It is possible that as the father's daily encounters with his infant increase, hand in hand with the infant's growing social skills from the second to the sixth month of life, the prolactin and oxytocin systems reorganise and create new connections, the researchers said their study published in the journal Hormones and Behaviour.

The hormones seem to rewire men's brains to make them more empathetic, according to Feldman.