Overview: Why sex? For one thing, with sex we're trying to stay ahead of the germs that are always attacking us. With one act of mixing our genes through sexual reproduction, there are millions of new possible combinations to help fight off the parasites. Includes an explanation of the relationship between sex and parasites, an experiment in which women use scent to detect subtle genetic differences in men, and a discussion of the risks organisms take in reproducing sexually rather than asexually.