From Encyclopedia of Sex and Sexuality
The song may go, “Birds do it, bees do it,” but there is a world of difference between what occurs in the animal and insect kingdoms and sexual intercourse between humans. Sexual intercourse is the act in which a man’s penis is inserted into a woman’s vagina and together they begin the rhythmic movement that may lead to male orgasm and the conception of a child. Sexual intercourse is also called coitus, which is drawn from the Latin root coire, meaning to go or to come together.
While sexual intercourse is obviously an integral part of the reproductive process and, therefore, basic to the very existence of the species, the solely reproductive aspects of sexual intercourse, as it has evolved among humans, have become only a small, one could almost say vestigial, part of the act. But while humans may have developed ways of reproducing that do not require actual sexual intercourse (see insemination by donor; In Vitro Fertilization), the act is no more likely to disappear from human physical activities than walking.
Humans have long faced one problem with reproduction. Having developed from apes, Homo sapiens branched off from their ancestors because of their larger brains. With this larger brain, however, the human baby could not pass out of the mother with a fully or even nearly developed brain. Much of the human child’s cranial development must take place outside of the womb, meaning that humans are burdened with the full-time care of helpless and fragile babies during the time this development takes place. This turns the relationship between the human male and female into a very complex one with many interactive elements, including a gamut of emotional attachments, many of which come together around the act of sexual intercourse.
One key development that arose over time was that in human beings sexual intercourse occurred throughout the year, not just when the female was ready to reproduce. This separated the sexual act from reproduction to such an extent that throughout the ages there have been people who are totally ignorant of the consequences that might arise from engaging in sexual intercourse. Even today this is something that has to be taught to young people, though one would think that something as important to the species as its own reproduction would be inately known. Of course, the safety measure that nature has taken against such ignorance to insure the continuation of the species is to have made the desire for sexual intercourse so strong that it cannot be ignored. That is why humans engage in sexual intercourse many more times than is needed for procreation, and continue to engage in it throughout their lives, long after the ability to reproduce has been lost by the female.
Humans are driven to seek sex by the libido, the part of the human psyche that creates the desire for sexual intercourse. Animals also share that desire, but we differ in that, intertwined with the desires instigated by our libidos, are the equally strong passions stirred by our hearts. Certainly not all acts of sexual intercourse are connected with the emotions we associate with love (if that were so, the world’s oldest profession—prostitution—would never have existed), but for us and the optimum functioning of our species, love is actually the more important of the two drives.
Humans also differ from other animals in the positions they use for intercourse. While humans have a whole repetoire of sexual positions, the most common one is labeled the “missionary position,” in which the man lies on top of the woman with their faces close together (in animals, males mate with females from the rear). This position facilitates communication between the partners, with words, visual stimuli, and kissing, again showing how important a role the brain plays in the total sexual act.
While technically the act of sexual intercourse can be considered to take place when a male and female human being place their genitals together, in a broader sense that act can be considered to begin much earlier. If a person sends his or her beloved a bouquet of flowers in the morning, it may begin an arousal process that will culminate in sexual intercourse that night. And since many women stay aroused for a long time after intercourse, those same flowers might trigger another episode of sexual intercourse the following morning. The conversation that takes place over a leisurely dinner is another ritual that often becomes part of the process of sexual intercourse. (The restaurant industry recognized this long ago and usually does its part to set the mood for romance and seduction by lowering the lights in the evening.) Other human behavior that is part of the process includes dressing provocatively, wearing certain scents, and dancing together closely.
The act of sexual intercourse has evolved over time, especially as women have been freed from the risk of pregnancy by effective contraceptive methods. Though in the past many women would engage in the act as a duty more than as a source of pleasure, modern women seek sexual gratification as much as their mates do. A woman requires physical stimulation of the clitoris in order to reach sexual satisfaction, but because of the location of the clitoris, she does not necessarily receive adequate stimulation from the movement of the penis inside her vagina. This need has resulted in what is now known as foreplay, an integral part of sexual intercourse, in which the woman’s clitoris is manipulated by her mate, either manually or orally, until she reaches a high enough state of stimulation to reach orgasm, either prior to the entry of the penis or after penetration.