3 - Contact, not conflict, causes the evolution of anisogamy

Abstract

In common with all religions, biology offers a creation story for male and female. Unlike religious myths, biology's creation stories are scientific claims and subject to scientific examination. Today, the mainstream evolutionary theories for the origin of male and female propose that sexual conflict causes the evolution of the distinction between males and females. In this chapter we propose instead that the male/female distinction did not arise from sexual conflict, but as a tactic to maximize the contact rate between gametes. This chapter follows closely the treatment in Iyer and Roughgarden (2008) and Roughgarden (2009).Anisogamy defines the distinction between the sexes – the male individual or organ is characterized by production of small gametes (sperm) and the female by the production of large gametes (eggs) (Stearns, 1987). Isogamy – the production of equally sized gametes, may be the ancestral condition because its occurrence is restricted to primitive taxa among algae, fungi, and protozoa (Bell, 1978). Hence the origin of males and females can be traced back to the evolution of anisogamy from isogamy. Kalmus (1932) was the first to propose a model for the evolution of anisogamy. He supposed that the size of gametes produced by each sex traded off against the number of gametes produced. Zygotes are formed by collisions between eggs and sperm and hence the number of zygotes produced by a population is proportional to the product of the total number of eggs and the total number of sperm produced by its members.