In the animal kingdom the mother is generally the parent that provides the most care to the young.  Males are running around competing for access to females, and don’t really have the time to stuff worms in little beaks or wipe noses.  The argument goes that females devote more resources to growing the young and so it’s in their best interests to ensure that they survive.  Guys just need to sow their wild oats and by the way they really don’t appreciate all the criticism.

But in some species it’s the males that provide most care to the young.  Seahorses are a commonly-cited example of this.  So, what’s up with these guys that they’re willing to be Mr. Mom?

This paper (open-access at Nature Communications) provides data suggesting that it’s the male/female ratio skew in these species.  If there are more males than females then access to females is restricted.  Males benefit more by staying close to their mates and raising the young.  Notably, female polygamy is also increased in these situations since the males are busy and the females are in-demand.

Mammals appear to be somewhat immune to this phenomenon, since males can’t make the milk necessary to feed the young.  And in humans, the parenting skills of most males places a powerful negative selection on the evolution of this behavior.

http://www.nature.com/ncomms/journal/v4/n3/full/ncomms2600.html