Some other things to think about regarding breeding:
It isn't necessarily the strongest that pass on their seeds. It is only the ones that survive long enough to breed. If it were only the strongest people that bred, there wouldn't be any engineers
Also, think about what attracts you to someone right when you see them. It is all things to make you want to pass the strongest traits to your offspring. Girls with nice bodies are usually in shape, which means that they would be able to escape danger more easily. Buff guys can defend the girls, and can be more dominant in the pack, and can hunt more effectively. All these knee-jerk reactions towards the opposite sex are attractions to strong evolutionary traits for humans.