ABSTRACT
At the cellular level, sex is the opposite of reproduction; in reproduction one cell divides into two, whereas it is the essence of the sexual process that two cells should fuse to form one. In this essay I shall ask what selective forces were responsible for the origin of the sexual process, and by what selective process is it maintained. It is easier to ask these questions than to answer them; the fact that we cannot answer them with confidence is a challenge to evolution theory.
