"For human males, strong, healthy breasts on a woman signal a good candidate for nurturing children. For females, strong, healthy buttocks on a male signal the ability to thrust hard & long, thereby improving the chances of fertilization."
That might be true, but it's also believed that it denoted to the woman that the said male would be a good provider; one who was a swift and fleet footed runner, and could chase after the prey.  Besides being fertile, women looked for mates who could bring home the venison.  Don't forget that with humans, it takes at least ten years before a child reaches a modicum of maturity.  That's a lot of time and effort, and historically usually required two parents to be successful.

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