One of the reasons men give for their dating struggles is that the majority of women are only interested in a minority of men, usually 80% of women going after 20% of men. While I doubt the ratio is actually that uneven, I think rule is true and was wondering if there's any research on this.

The only hard evidence I can think of is the fact that men send out so many more messages on online dating than women. Implying that men are at least willing to give most women a chance while most women only care for the top men. Anyone have any other studies?