Female, Male. Man or Woman? duality.  biological function. Sex in bed or out of bed.  Up or Down?  make babies or for fun? sex education can help you along.  Sex is universal binary of the ages, its the one thing we share with most other life-forms.  watch and learn.

this lower section is an excerpt from wikipedia...

Animal sexual behavior takes many different forms, even within the same species.  Researchers have observed monogamy, promiscuity, sex between species, sexual arousal from objects or places, rape, necrophilia, sexual orientation (heterosexuality, homosexuality, bisexuality and situational sexual behaviour) and a range of other practices among animals other than humans. Related studies have noted diversity in sexed bodies and gendered behaviour, such as intersex and transgender animals.