Psychological and Sociological Viewpoints
For many years the common assumption, shared by many scientists and religious communities, was that the natural and normal human sexual orientation is exclusively for the opposite sex (heterosexual). Sexual studies carried out during and after the 1950s lead psychologists and doctors to recognize homosexuality as a second exclusive orientation. Since then similar acceptance has grown for non-exclusive orientations, such as bisexuality.
Sigmund Freud famously characterized humans as naturally "polymorphously perverse," meaning either that practically any object can be a source of erotic fulfillment, or that babies are relatively indifferent to the object of erotic fulfillment. Freud argued that as the child grows, the objects of erotic fulfillment become more clearly defined and limited (whether this is the result of a biological or a social process is a matter of debate). Anthropologists have observed that around the world many people, including people within the same culture, may be oriented towards a variety of objects. Nevertheless, most scholars assume that in any given society what is considered an appropriate object of desire is highly regulated and limited. Moreover, some cultural traditions (especially religious) assert that people should have only one class of objects of desire.
According to two controversial studies, Sexual Behavior in the Human Male (1948) and Sexual Behavior in the Human Female (1953) by Dr. Alfred C. Kinsey, when asked to rate themselves on a continuum from completely heterosexual to completely homosexual, and when the individuals behavior as well as their identify is analyzed, the majority of people appear to be at least somewhat bisexual, i.e., most people have some attraction to either sex, although usually one sex is preferred. According to Kinsey, only a minority (5-10%) can be considered fully heterosexual or homosexual. Conversely, only an even smaller minority can be considered fully bisexual. This led Kinsey to propose the what has since become known as the Kinsey scale.
More recently, attempts to define human sexuality which factor in concepts of changing sexuality over a persons lifetime and their internally perceived ideal state, such as the Klein Sexual Orientation Grid, have been put forward.
Most modern scientific surveys find that the majority of people report a mostly heterosexual orientation. However the relative percentage of the population that reports a homosexual orientation varies with differing methodologies and selection criteria. Most of these statistical findings are in the range of 2.8 to 9 percent of males, and 1 to 5 percent of females for the United States (source: [1], page 24 -- this figure can be as high as 12% for some large cities and as low as 1% percent for rural areas). Almost all of these studies have found that homosexual males occur roughly at twice the rate as homosexual females. Estimates for the percentage of the population that identify as bisexual vary widely based on the type of questions asked. Some studies only consider a person bisexual if they are nearly equally attracted to both sexes, and others consider a person bisexual if they are at all attracted to the same sex (for otherwise mostly heterosexual persons) or to the opposite sex (for otherwise mostly homosexual persons). (need to find the current estimates and ranges for the percent of the population that identifies as bisexual)
A very small percentage of people are not sexually attracted to anyone (asexuality).
For more see: Anthropological classification of homosexuality
Biological Viewpoint
Neurological studies have shown that certain regions of the brain are different between heterosexuals and homosexuals. In particular, the Third Interstitial Nucleus of the Anterior Hypothalamus (INAH-3) is much smaller in homosexual men and in heterosexual women than in heterosexual men and in homosexual women. This result was first found by neuroanatomist Simon LeVay, a researcher at the Salk Institute, when dissecting the brains of 41 deceased hospital patients. [1]
Simon LeVay's finding points out a correlation between physiology and sexual orientation, but does not necessarily establish -- by itself alone -- a genetic basis for homosexuality.
Religious and Moral Viewpoints
Much religious teaching maintains that sexual behavior should conform to moral and religious codes. For example, Christianity has traditionally considered homosexuality to be morally wrong. Recently, the level of acceptance of homosexuality within christianity has, in general, increased.
Wider issues of sexual morality are also considered by many religions. Some religions advocate chastity or celibacy for some members, and many religions condemn incest and bestiality. Often religious views of sexual orientation are based on considerations of what seems natural.
For more see:
Sexual orientation as a "construction"
Many people in Western societies today speak of sexual orientation as a unified and actual thing. Over the past thirty years some anthropologists, historians, and literary critics have pointed out that it in fact comprises a variety of different things, including a specific object of erotic desire, and forms of erotic fulfillment (i.e. sexual behaviors). Some scholars have argued that "sexual orientation" and specific sexual orientations are historical and social constructions. In 1976 the historian Michel Foucault argued that homosexuality as a concept did not exist as such in the 18th century; that people instead spoke of "sodomy" (which involved specific sexual acts regardless of the sex of the actors) as a crime that was often ignored but sometimes punished severely (see sodomy law). He further argued that it was in the 19th century that homosexuality came into existence as practitioners of emerging sciences as well as arts sought to classify and analyze different forms of sexual perversion. Finally, Foucault argues that it was this emerging discourse that allowed some to claim that homosexuality is natural, and therefore a legitimate sexual orientation.
Foucault's suggestions about Western sexuality led other historians and anthropologists to abandon the 19th century project of classifying different forms of sexual behavior or sexual orientation to a new project that asks "what is sexuality and how do people in different places and at different times understand their bodies and desires?" For example, they have argued that the famous case of some Melanesian societies in which adult men and pre-pubescent and adolescent boys engage in oral sex is not comparable to similar acts in the United States or Europe; that Melanesians do not understand or explain such acts in terms of sexual desire or as a sexual behavior, and that it in fact reflects a culture with a very different notion of sex, sexuality, and gender. Some historians have made similar claims about so-called homosexuality in ancient Greece; that behaviors that appear to be homosexual in modern Western societies may have been understood by ancient Greeks in entirely different ways.
At stake in these new views are two different points. One is the claim that human sexuality is extraordinarily plastic, and that specific notions about the body and sexuality are socially constructed. The other is the fundamentally anthropological claim of cultural relativism: that human behavior should be interpreted in the context of its cultural environment, and that the language of one culture is often inappropriate for describing practices or beliefs in another culture. A number of contemporary scholars who have come to reject Foucault's specific arguments about Western sexuality nevertheless have accepted these basic theoretical and methodological points.
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