It wasn’t until the turn of this century that researchers discovered a fascinating detail about men: Our bodies transform when we become fathers. (And it's not about the second trimester–size belly bump we fight into old age.)

Whether we’re biological dads or adoptive ones, heterosexual or queer, our hormonal systems alter dramatically when we become parents—an amazing revelation basically implying that despite the narrow role we fathers have straitjacketed ourselves into for so long, our internal chemistries may have always been nudging us toward more involvement.

We’ve long known that oxytocin—the “love hormone”—plays a role in a mother’s initial bonding with her child after birth. But more recently, researchers have observed that the same spike in oxytocin occurs when fathers hold and play with their newborns.

All of the internal changes can depend on how much time dads spend solo with their kids in infancy and toddlerhood. Having time where the man is responsible for direct physical interaction with an infant—not just being in the room, but actually providing care—has the biggest influence on his hormonal levels changing.

Sources- todaysparent.com