Is there a biological reason for female orgasm?

The purpose of an orgasm isn't solely to make you feel good. The biological purpose is to better the odds that this union between sperm and egg takes place.

On the woman's side, the mucous membranes that line the vaginal walls release fluids during intercourse so that the penis can slide with just the right amount of friction. As intensity and sensations build, the woman's brain tells the vagina and nearby muscles to contract. That contraction brings the penis in deeper and increases the chance of his sperm getting closer to the target. During an orgasm, the cervix, located at the top of the vagina, dips down like an anteater, and sucks semen in the cervix (the bottom of the uterus). The sperm is trapped in the cervical mucus until the release of the egg, and a signal then lets the sperm start the competitive swim up into the uterus.