Testing the adaptive selection of human mtDNA haplogroups: an experimental bioenergetics approach.

The evolution of human mtDNA (mitochondrial DNA) has been characterized by the emergence of distinct haplogroups, which are associated with the major global ethnic groups and defined by the presence of specific mtDNA polymorphic variants. A recent analysis of complete mtDNA genome sequences has suggested that certain mtDNA haplogroups may have been positively selected as humans populated colder climates due to a decreased mitochondrial coupling efficiency, in turn leading to increased generation of heat instead of ATP synthesis by oxidative phosphorylation. If this is true, implying different evolutionary processes in different haplogroups, this could potentially void the usefulness of mtDNA as a genetic tool to study the timing of major events in evolutionary history. In this issue of the Biochemical Journal, Taku Amo and Martin Brand present experimental biochemical data to test this hypothesis. Measurements of the bioenergetic capacity of cybrid cells harbouring specific Arctic or tropical climate mtDNA haplogroups on a control nuclear background reveal no significant changes in coupling efficiency between the two groups, indicating that mtDNA remains a viable evolutionary tool to assess the timing of major events in the history of humans and other species.