Here's the data behind these conclusions....
Fathers Experience A Testosterone Dip, An Oxytocin Spike
In 2014, a team of scientists at Emory University recruited 88 heterosexual, biological, married fathers of children between the ages of 1 and 2, for an unprecedented experiment. They tested their hormone levels among other metrics and compared these results to a group of 50 non-fathers. One of the most striking results is depicted below. Compared to non-fathers, dads had lower levels of testosterone, a male hormone linked to aggression, and higher levels of oxytocin, a hormone thought to play a role in maternal (and now, perhaps, paternal) attachment. The findings suggest that fathers, not just mothers, experience hormonal changes to help them adapt to their new roles as highly attached and less aggressive caregivers.
Dad Brains Change, Too
After running the hormone analysis, the researchers took the experiment one step further. They hooked each man up to an fMRI-which measures activation of different brain regions-and show him images of children and adults making happy, sad, and neutral faces. In the middle frontal gyrus, a brain region responsible for face emotion processing, fathers' brain activities spiked for children's faces significantly more than for adult faces. As depicted below, non-father brains made no such distinction. The results suggest that fathers' brains change, too, helping them augment empathy towards children.
It's Not Just Your Body And Brain: It's Your Wallet
Beyond the biological implications of fatherhood, studies have shown that men with children experience psychological and social changes, too. But, unlike women who take pay cuts when they give birth, the financial impact of fatherhood on men is quite positive. The data below comes from City University of New York research, which found that fathers in the city have made more money, on average, than non-fathers since at least 1990. It is unclear whether the sudden burden of diapers and saving for college drives men to earn more, or whether it's simply wealthier men who choose to start families. But one thing is clear from the preponderance of research-fatherhood changes men. Financially, hormonally, and neurologically.