The Biology of Sex
In this special Cell Picture Show, presented by Current Biology, we pay homage to the fascinating biology of sex. Sex is a paradoxical phenomenon: not only because pleasure and pain are often so close together, but also because it’s such a fundamental aspect of life. Yet biologists are still trying to understand why it exists in the first place. Sexual reproduction is everywhere—nearly all life forms practice it one way or the other. But sex as we know it comes at a cost: because there are two sexes, the reproductive output is essentially cut in half (two individuals are needed to reproduce). So, there must be significant benefits to outweigh these costs, or else sex wouldn’t have evolved.
Many theories have been put forward for what these benefits might be—in particular, increased genetic variation and the protection against diseases and parasites that comes with it. But the deeper reasons for the ubiquity of sex are still not fully understood. All the more reason, we think, to marvel at the many ways that sex is implemented in biology. Nearly all of the plants and animals that we see around us are the product of the fusion of two gametes: the female oocyte and the male sperm or pollen. Bringing these gametes together is a game of baroque intricacy. Because reproductive success is its ultimate prize, evolution has led to a host of complex adaptations that underlie all steps of sex—from the differentiation of the sexes and the production and delivery of the gametes, all the way to the complex signals, rituals, and combats involved in finding the right mating partner.