Sexual development and the evolution of sex determination.

The evolution of sex had profound consequences for life on earth as it brought about the origin of males and females. Yet understanding the amazing variety of mechanisms employed by organisms to produce males and females has evaded scientific explanation. Developmental biology provides essential insight to understand how the sexes are formed, and how the regulatory network underlying sexual development changes over evolutionary time. This is a critical step in revealing why the diversity of mechanisms arose in the first place. Here I present significant reciprocal contributions made by evolutionary genetics and developmental biology that bear on this question. In particular, I explore how changes in the timing of events during development can be viewed as heterochronic changes that alleviate the strong selection on the master trigger of male and female sexual development, enabling the evolutionary transitions between genotypic and environmental sex determination. 2008 S. Karger AG, Basel.