Abstract
Biological theories of sexual orientation, typically presented in human sexuality classes, are considered by many social psychologists to cause reductions in students' sexual prejudice. Yet when biological theories were not presented to 36 psychology students in a 10-week seminar on lesbian, gay, bisexual and transgender (LGBT) psychology, both sexual prejudice and two forms of essentialist thinking reduced significantly. Prejudice reduction was causally related to decreased essentialist belief in clear boundaries between sexual orientation categories but not to decreased belief in the immutability of sexual orientation categories. Students characterised belief in the fluidity of sexual orientation categories as enlightened and empowering in their own words. This cross-lagged study confirms earlier cross-sectional studies showing that sexual prejudice is causally related to ‘natural kind’ beliefs about sexual orientation. It further shows that the typical practice of teaching human sexuality courses from a biological perspective is not the cause of prejudice reduction in this educational context.