Human sexuality

Human sexuality is how people experience the erotic and express themselves as sexual beings; the awareness of themselves as males or females; the capacity they have for erotic experiences and responses.[1] Human sexuality can be described as the way someone is sexually attracted to another person of the opposite sex (heterosexuality), to the same sex (homosexuality), to both sexes (bisexuality), or attracted to no sexes in a sexual way (asexuality).[2]

It used to be believed that human sexual behavior was different from the sexual behavior of most other animals, in that it was practiced for reasons besides copulation. Current understanding is that many species that were formerly believed monogamous have now been proven to be promiscuous or opportunistic in nature; a wide range of species appear both to masturbate and to use objects as tools to help them do so, where procreation is not the aim. See animal sexual behaviour.

The term human sexuality can also cover cultural, political, legal and philosophical aspects. It may also refer to issues of morality, ethics, theology, spirituality or religion and how they relate to all things sexual.

Nature versus nurture debate
Like all things in biology, there is no simple answer.

Sexual drives among heterosexuals, homosexuals, bisexuals, and others are all driven partially by their genetics and also by superior mental activity and by social, cultural, educational, and normative characteristics of those places where the subjects grow up and their personality develops.

Each of these sexual lifestyles will then drive personal identity and in the social evolution of individuals. And will be a powerful force that affects all social activities.
Evidence for nature

Twins are more likely to share sexual orientation than other close genetic ties. This is probably due to their identical genes and similar en utero chemicals.

Biology and physiology
The biological aspects of humans' sexuality deal with human reproduction and the physical means with which to carry it out. They also deal with the influence of biological factors on other aspects of sexuality, such as organic and neurological responses, heredity, hormonal issues, gender issues and sexual dysfunction.

For the sake of reproduction, normally a male will stimulate a woman until she is ready to have sex. Then he will penetrate her vagina with his penis. After repeated thrusts of his midsection and buttocks—causing the penis to partially retract from, then reenter, the vagina—the man will ejaculate his semen. This may lead to insemination, which may lead to pregnancy.

During this time there are many other biological changes which have little or nothing to do with reproduction and can be generalized to any sexual act, not just that between a man and a woman. These include, increase in body temperature, increase in levels of pleasurable hormones.
Continued 

Original link