Why is there sex and why has sex evolved? These are some of the biggest questions in evolutionary biology. This book discusses the theories of advantages and disadvantages of sex. There are various hypothesis about the reasons for self-reproduction and outcrossing, respectively, but relatively few experimental studies have been carried out. Caenorhabditis elegans is a suitable organism investigating these questions, because it can self-fertilize and outcross. The main aim of my thesis is to discover whether Caenorhabditis elegans males have a function and if so investigate what might it be. My thesis consists of three parts. First I asked what causes the difference in male maintenance between two different strains. Second: I tested if males might facilitate the spreading of genotypes into resident populations. Third: I subjected populations of Caenorhabditis elegans to changing physical or biological stress and asked if this selection pressure leads to populations with higher male maintenance. At the end sex is maybe just so much fun!