Sexual Selection in Penises and Clitori

In species that do not use copulatory thrusting, especially insects, penises evolve more obvious tactile stimulators: nubs, spikes, ridges, curls, barbs, hooks, and flagella. Male insects often try to push each other off during copulation, so copulatory thrusting would risk disengagement. Better to lock the genitals together and have internal flagella to excite the female. With primates, it is not so common for male rivals to swarm over females knocking each other off. This allows couples a ...

 Evidence of Sexual Selection in Humans

By primate standards, humans look strange, even after we step out of our sport utility vehicles. Compared with other apes, we have less hair on our bodies, more on our heads, whiter eyes, longer noses, fuller lips, more expressive faces, and more dextrous hands. In most species, sexual ornaments like long head hair, hairless skin, and full lips would have evolved only in males, because females would have been the choosy sex. Males have few incentives to reject any female mates. The fact that ...