From the chemical to the transcendental, Valerie Monroe counts the whys.

Why do we do it?

A young woman talks about the slow death of her mother. She has cared for her for many long months. Throughout all the arrangement making, the tension, the sorrowful, relentless accretion of evidence of the inevitable, she doesn't express her fear or her sadness or her grief. She talks about it, but her feelings sit heavily as stones on her heart, and won't be moved by words.

One night, she says, she was making love with her boyfriend, looking into his eyes.

She felt secure in his embrace, cradled in the steady, loving constancy of his touch and his gaze. The shared rhythm of their bodies both comforted and aroused her in a delicate balance of pleasure. But as he rocked with her in his arms, she began to feel a giving-way, the heaviness moving, her hold on her feelings relaxing. All of a sudden, her heart seemed to crack open and, to her deep surprise, grief poured from her in a tide of tears. "My mother!" she cried, eyes locked with her lover's. "My mother is dying!" It was the very first time she had been completely present with that fact, understanding it, accepting it, knowing it.

Her boyfriend pulled her closer, holding her tight. "I love you, l love you, l love you," he said.

I don't guess they asked each other afterward, "Was it good for you, too?" Sometimes "good" just isn't adequate to describe an experience that has been referred to as the little death. Did you know that during orgasm, most of the of satisfaction and attachment? A study has found that women who regularly receive semen vaginally are less depressed than those who don't, says Helen Fisher, PhD, author of Why We Love, The Nature and Chemistry of Romantic Love. This could be because they really like their partners; it could also be because seminal fluid is awash not only with testosterone and estrogen but also with chemicals such as dopamine and norepinephrine, serotonin, and oxytocin, which can contribute to either elation or calm. Another recent study revealed the unsurprising result that the more often a person has sex, the happier he or she is. This could be because people who have sex often are more likely to be healthy and enjoying a good relationship. It could also be because sex exercises the muscles and the respiratory system; gets the circulatory system moving, which gives the skin a gorgeous glow; and according to Fisher's research, triggers the brain circuitry for romantic love and attachment. Why do we do it? Because it's fun. Because it can be the most powerful, concrete way to demonstrate love for ourselves and for someone else. Because sex helps us to remember. Because it helps us to forget. Because when we open ourselves to the experience completely, we become intimate with the world in a way that's otherwise inaccessible, and unique. Flooded with hormones that can release us from the moorings of self-consciousness and control, we can relax into a presence of mind that allows boundaries, momentarily, to dissolve. Sex can not only help us feel better—it can also help us to feel.