The developmental instability theory explains homosexuality as a perturbance of the complex processes of prenatal brain development by exogenous influences and was originally stimulated by findings of increased non-right handedness among homosexuals of both sexes (Lalumière, Blanchard, & Zucker, 2000 ), but attempts at finding an association of homosexuality with fluctuating asymmetry as a broader index of developmental instability have been unsuccessful (Rahman, 2005 ).
Source: wiktionary