  Oh man this is why bio is so fun! Ok well at least this is why this chapter is so fun! Warning this is kind of graphic, but then again it is coming straight from my bio book: Humans and several other primates are unusual in having no distinct mating periods; females are potentially receptive to males throughout the year.
In humans, the sexual behavior called "making love" may have evolved as a way to strengthen the bond between mates, as well as to promote the union of egg and sperm. Our sexuality is emotional as well as physical, and we have highly varied sexual expression. The physical events of the human sexual respone occue in a sequence of four phases. During the excitement phase, sexual passion builds, the penis and clitoris became erect, and the testes, labia, and nipples may swell. The vagina secretes lubricating fluid, and muscles tighten in the arms and legs. These responses continue during the plateau phase, which is marked by increases in breathing and heart rates. Orgasm follows, characterized by rhythmic contractions of the reporductive structures, extreme pleasure for both partners, and ejaculation by the male.
The resolution phase reverses the previous responses; the structrues return to normal size, muscles relax, and passion subsides. Hahaha, I love it, I really do. It's funny because I bet so many people have gone out and had sex after reading that, haha school makes sex sound exciting and "enjoyable. " Haha, not too often school makes you horny, lol. Ok me done. 
