On: Most young men are single. Most young women are no...

[polotics]

...and are unknowingly sharing some studs.

[ryandrake → polotics]

...or knowingly sharing. Some women would rather non-exclusively have a partner they perceive to be high value than exclusively have a partner they perceive to be low value. I've heard it put as: "I'd rather have 25% of a winner than 100% of a loser."