Biology and the Single Girl

Wow, today it crossed my mind that most of the couples I know may be together for reasons that are............biologically-driven. If they don't share the same hair color, they are the same height with similar body shapes or of the same ethnic background. It's all about reproduction! How much of our behavior is driven by our biology? Are we trapped in a merry go round of behaviors driven by the need to pass on our characteristics? I am, of course, ready to swear up and down that the reason I check out every attractive redhaired man I see has nothing to do with biology. It's hair loyalty! Ok, it's also unusual. Biology? Nah.