The transformation of the ancient world from paganism to Christianity brought with it not only a new set of ethical injunctions, but a new 'moral cosmology'—that is, a new way of conceiving of humanity in relation to God and the cosmos. One important element of such a moral cosmology is the distinction between the sexes. Why did God create humanity in two sexes, and what is the ultimate meaning of one’s sexual identity? The thought of the Greek Fathers on this subject was heavily indebted to that of Greek philosophy, especially Plato. For Plato the soul is fundamentally sexless and acquires sexual identity only upon embodiment. Although Christians (with the exception of Origen) generally rejected the pre-existence of the soul, they accepted the premise that the soul itself is intrinsically sexless. Many carried this further to the conclusion that in the afterlife there will be a gradual movement away from our current sexual condition to a higher, asexual form of existence. This chapter traces the development of such views from Plato through Gregory of Nyssa and Maximus the Confessor. It further argues that on this point Christian authors accepted the pagan philosophical inheritance rather too uncritically, and that a careful consideration of their rejection of metempsychosis suggests a very different view.