The sheep offers a unique mammalian model in which to study paradoxical same-sex sexual partner preferences. Variations in sexual partner preferences occur spontaneously with as many as 8% of rams in a population exhibiting a sexual preference for other rams (male-oriented). The current review presents an overview and update of the male-oriented ram model and discusses several theories that have been invoked to explain same-sex preferences in this species. Although our understanding of the biological determinants and underlying neural substrates of sexual attraction and mate selection are far from complete, compelling evidence is discussed that supports the idea that neural substrates regulating sexual partner preferences are organized during prenatal development. The challenge for future research will be to construct an integrated picture of how hormones, genes, and experience shape sexual partner preference. (C) 2011 Elsevier Inc. All rights reserved.