A critical discourse developed in the 1990s in order to deconstruct (or ‘to queer’) sexuality and gender in the wake of gay identity politics, which had tended to rely on strategic essentialism. Opposed to gender essentialism, queer theorists see sexuality as a discursive social construction, fluid, plural, and continually negotiated rather than a natural, fixed, core identity. ‘The representation of gender is its construction,’ declares the Italian-American feminist theorist Teresa de Lauretis, who coined the term ‘queer theory’ in 1990. Butler, seeking to destabilize binary oppositions such as gay/straight, introduced the key concept of performativity. Queer theorists foreground those who do not neatly fit into conventional categories, such as bisexuals, transvestites, transgendered people, and transsexuals. Existing movements which have been significant influences are feminism and poststructuralism (particularly the methodology of deconstruction). Foucault's influence has also been of central importance, particularly his argument that homosexuality (and indeed heterosexuality) as an identity emerged only in the late 19th century. Queer theory has itself been a significant influence on cultural and literary theory, postcolonialism, and sociology, and ‘queering’ is now applied also to the ‘boundaries’ of academic disciplines.