OK, Imagine a world where there are no men, and women reproduce by asexual cloning. The world would be populated entirely by women.
All alike. Same hair, same eyes, same legs, same...everything! The world population would increase to about a dozen women. Each
exactly the same. Then someone would have a birthday party and they'd all show up in the same dress. In absolute lunacy, they'd all murder each other. End of humankind.
With men there, however, each man tells his woman, "No, honey.
Her dress is just a cheap knockoff!"
The race is preserved!