It takes a passionate look at the evolution of sex, which allows a species to pass its genes along from generation to generation. Sex is everywhere. Bees do it and birds do it — and so do lizards and bacteria. In its simplest form, sex is the process of mixing genes from two parents into a new offspring. This gene swapping ensures that each generation is just a bit different from the one that came before, and that each individual is a bit different from others.