The "Why" of desire:

What makes us want sex? Is it only that we, like other animals, possess a primitive need to mate and propagate? Or are our sexual urges, like ourselves, more highly evolved? What is libido? Is it purely physical attraction, or is it fed by fantasy -- those wonderful day (and night) dreams that make us feel aroused? What prompts us to engage in sexual stimulation? Must we have a partner? Need it be someone we know, or can it be an idealized model in formal attire at the Academy Awards or, better yet, in a bathing suit in the Bahamas?

The answer to these questions is yes, yes, and, oh yes! (And we haven't yet even gotten to the subject of orgasm.) Libido is a product of our psychological, social and physical development. It is where our bodies meet up with our culture, our instincts -- and what our parents and teachers taught us.

All these libidinous issues have kept the psychologists and sociologists very busy. But what about the biologists? Our sexual urges start in ancient centers in our brain that are fundamental to the propagation of our species. Hidden in the recesses of our hypothalamus and limbic system are intricate hormone receptors that bind with and are turned on by estrogen, progesterone, male hormones, prolactin, endorphins and possibly pheromones. These and other brain cells don't get their information just from hormones but also from chemicals called neurotransmitters, which form our link with the outside world.