Population size does not influence mitochondrial genetic diversity in animals. Science 312:570–2

Within-species genetic diversity is thought to reflect population size, history, ecology, and ability to adapt. Using a comprehensive collection of polymorphism data sets covering È3000 animal species, we show that the widely used mitochondrial DNA (mtDNA) marker does not reflect species abundance or ecology: mtDNA diversity is not higher in invertebrates than in vertebrates, in marine than in terrestrial species, or in small than in large organisms. Nuclear loci, in contrast, fit these intuitive expectations. The unexpected mitochondrial diversity distribution is explained by recurrent adaptive evolution, challenging the neutral theory of molecular evolution and questioning the relevance of mtDNA in biodiversity and conservation studies. G enetic diversity is a central concept of evolutionary biology that has been linked to organismal complexity (1), ecosystem recovery (2), and species ability to respond to environmental changes (3). A lack of diversity is typically considered as evidence fo