Queer theory is a theory about sex and gender within the larger field of Queer studies. It proposes the theory that one's sexual identity is partly or wholly socially constructed, and therefore individuals cannot really be described using broad terms like "homosexual" or "woman." It challenges the common practice of compartmentalizing the description of a person to fit into one particular category.
In particular, it rejects the creation of an artificial and socially assigned categories and group-entities based on the division between those who share some habit or lifestyle and those who do not, The Other. Instead, queer theorists suggest building up categories and groups by voluntary and especially aesthetic associations.
Earlier historical influences include Jacques Lacan, Louis Althusser, and Jacques Derrida. The primary influence in the development of Queer theory was Michel Foucault; later theorists include Judith Butler and Eve Kosofsky Sedgwick.
Like those in some branches of feminism, many scholars in Queer theory view prostitition, pornography and BDSM as legitimate and valuable expressions of human sexuality. For example, Patrick Califia in Feminism and Sadomasochism (ISBN 1573440965) writes about how sadomasochism encourages fluidity, and questions the naturalness of binary dichotomies in society: "The dynamic between a top and a bottom is quite different from the dynamic between men and women, blacks and whites, or upper- and working- class people. That system is unjust because it assigns privileges based on race, gender, and social class. During a S/M encounter, roles are acquired and used in very different ways. If you don't like being a top or bottom, you switch your keys. Try doing that to your biological sex or your race or your socioeconomic status."
This point of view places them in conflict with branches of feminism that view prostitution, pornography, etc. as mechanisms for the oppression of women.
Critics of queer theory hold that a vast and growing body of physiological, genetic and sociological evidence shows that, scientifically speaking, sexual orientation and sexual classification are more than just social constructs. In this view, various biological characteristics (some of which are genetically heritable) play an important role in shaping sexual behavior. (Part of the larger nature versus nurture debate.) Many scientists hold that deconstructionist claims about science (not only on this topic) are pseudoscience.
Many different commentators respond to these claims by noting that not all individuals are clearly classifiable as either "male" or "female", even on a strictly biological basis. For example, the sex chromosomes (X and Y) may exist in atypical combinations (as in Klinefelter's syndrome [XXY]). This complicates the use of genotype as a means to define exactly two distinct genders. intersexed individuals may for many different biological reasons have ambiguous genitalia.
The way the question of the innateness of sexual identity and gender identity has played out in the work of one serious researcher can be investigated by following the many works on sexology of the Johns Hopkins University researcher, Dr. John Money. Early works indicate that he was much impressed by the argument that one's gender identity is a social construct, but in later works he develops a highly nuanced account of all the inputs that research implicates in the formation of any individual's gender identity.
The biological aspects are not as relevant to those who view the process of construction as taking place within natural language and categories it forms by frequent reinforcement in minds - pronouns for instance that make gender or formality distinctions. In Jacques Lacan's model of psychology, the mirror stage (around age 3 where a child sees themselves in a mirror and believes that image to be their "self") and development of language occur at approximately the same time. Indeed, it may be language that constructs the entire idea of self, and gender/sex distinctions as well. Ferdinand de Saussure's ideas of sign-signifier relationships in language are used to demonstrate this concept as well. It is seen that although some biological truths may exist, our knowledge and conceptualization of them is always mediated by language and culture.
Hybrid theories which combine the notions of innate characteristics and social constructs also exist. For example, one might hypothesize that social customs, expections, identities, are shaped by certain "facts of life." This might include innate structures ranging from the obvious (like differences between reproductive organs) to the controversial (such as the existence of a sexual orientation which is fixed in early life with genetic, environmental, and other factors determining the outcome). Empirical (scientific) investigation might be used to separate truth from conjecture and explain how these "facts of life" interact with social norms. The role of Queer theory would be to examine the biological notions of sexual orientation and gender in the context of culture and history.