If sex is not just about reproduction, it is not just about genes, XY chromosomes, and hormones either. Sex is introduced to explain skeletal structure, mental aptitude, posture, emotional disposition, aesthetic preference, body fat, sexual orientation and responsiveness, athletic ability, social dominance, shape and weight, artistic ability. It is also supposed to explain any number of so-called "instincts", including the nesting instinct, the maternal instinct, and perhaps even the Budweiser instinct.
