Vital Question: Energy, Evolution, and the Origins of Complex Life

by Nick Lane

The puzzle is that sex is ubiquitous among eukaryotes. One might think that the advantages would offset the costs under certain circumstances but not others. To a point this is true, in that microbes may divide asexually for 30 generations or so, before indulging in occasional sex, typically when in a state of stress. But sex is far more widespread than seems reasonable. This is probably because the last common ancestor of eukaryotes was already sexual, and hence all her descendants were sexual too. While many microorganisms no longer have regular sex, very few ever lost sex altogether without falling extinct. The costs of never having sex are therefore high. A similar argument should apply to the earliest eukaryotes. Those that never had sex – arguably all those that had not ‘invented’ sex – were likely to fall extinct.