Sexual intercourse has been occurring on the planet ever since the first non-protozoon animal has evolved. Even after various ages of evolution, sexual intercourse is still the only means to reproduce for higher organisms. There are several sophistications where sexual intercourse is concerned, and in the human, the highly evolved of all the animal species, sexual intercourse takes a different meaning altogether.

It can be rightfully said that the human being is the only organism that derives the full pleasure of sex, and makes deliberate efforts to make the process much more fulfilling. Most importantly, the sexual intercourse is a very necessary device to strengthen the emotional ties between married partners and make them actually believe that they are like two bodies with a single soul. In the human being, the sexual intercourse is an act that involves all the five senses - sight, sound, smell, taste and touch - and is a very elaborate process of mutual stimulation.

In the most basic sense, sexual intercourse is the penetration of the male penis into the female vagina for sexual satisfaction. However, this definition is grossly incomplete, as the total intercourse act is a much more intricate process, working at various levels. The process begins with physical attraction, which develops naturally in both males and females in their early puberty. This is when the changes in their own bodies intrigue them, and they are intrigued also by the differences in the bodies of the opposite sex. Up until this stage, both boys and girls do not have much of shame about their bodies, but after the pubertal realization, they would keep their bodies and the changes occurring in them as a personal secret.

From this attraction, develops infatuation for a particular person. Both boys and girls are infatuated with several members of the opposite sex in their early days. This is a period of much awkwardness, when the child is unable to give vent to feelings, and at the same time not understand fully well what is happening. The first sexual experience may happen early or late, depending on the level of sexual attraction between the partners and the opportunity, among other factors. This is when the first sexual intercourse may occur. This may actually be more of a harrowing experience than satisfying for both the boy and the girl. But still there is an unexplained yearning to have more of the same. As time passes by, both partners gain in experience and this is when sexual intercourse begins to become fun.

Talking about the mechanics of sexual intercourse, it all begins with the titillation. The changes are seen quite easily in the male, with the erection of the penis. Even the nipples might become erect to a small extent. The stiffening of the nipples is seen much more prominently in women. In women, there is also lubrication of the vagina, which indicates that it is receptive to the penis.

Foreplay follows, which can take several forms depending on the preference of the partners. The usual foreplay is done by fondling and caressing the bodies. Oral sex may be performed by both partners on each other (if a man stimulates the woman's genitals, it is called cunnilingus; if a woman stimulates the man's genitals, it is called fellatio). Oral sex is a precursor to the actual penetrative sexual intercourse.

When the man is fully aroused, he would penetrate his penis within the vagina. The penis is then moved back and forth, with the impetus for the movement provided by either the male or the female. Sexual climax for the male is reached when he ejaculates his seminal discharge. The woman finds her climax when she is fully aroused. This is felt by a characteristic quivering of her body; however this may not always be observed.

Sexual intercourse is the device by which reproduction takes place. The male ejaculate contains the sperm, which is the male gamete. It unites with the egg cell of the female to form the embryo. However, every sexual intercourse does not lead to a pregnancy. A female can become pregnant only on specific days of her menstrual period.

Another big issue with sexual intercourse is of STDs or sexually transmitted diseases. A host of dangerously contagious diseases are transmitted only through sexual contact. The most prominent among these diseases are syphilis and gonorrhea. There are hundreds of thousands of cases of syphilis and gonorrhea recorded every year, even in the developed countries. One bigger scare than these diseases is that of an AIDS infection. Sexual intercourse is the leading cause of the transmission of AIDS, even leading it to become an epidemic in certain populations of sexually active people.

Unsafe sex is the main reason for the transmission of these diseases. The risk of these can be reduced to a great extent by the correct use of condoms.

However, the greatest advice would be to avoid any kind of illegal sexual contact. All branches of medicine advocate monogamy strongly, i.e. to remain sexually faithful to only one partner. Not only is it healthy, but your sex is the best gift you can give to someone you love. One must not squander it away recklessly.