Northwestern University reasearchers discovered that fatherhood makes men less manly. A study of men in the Phillipines found that those with higher testosterone levels were more likely to become fathers. 
But once the babies were born, their testoserone levels dropped. They say it shows that men are hardwired by evolution to have kids, then stay and help raise them. And the more the men do to help care for the kids, the farther their testoserone level drops.
- At this point Brad Pitt has absolutely no testosterone but a whole lotta estrogen!
- Apparently this rule about sticking around to help with the kids doesn’t apply to a large number of professional athletes.