It turns out that being an involved dad may actually alter a man's hormone levels. A study  of male testosterone levels found that the more time men spend parenting their children, the lower their testosterone levels.
Experts say this suggests that men’s bodies evolved hormonal systems that helped them commit to their families once children were born. It also suggests that men’s behavior can affect hormonal signals their bodies send, not just that hormones influence behavior.
But most importantly, this reinforces the idea that mothers were biologically meant to have child care help. So go ahead and strap that baby sling on your hubby!