John has an
interesting post up which reviews data that certain high latitude mtDNA lineages might confer a functional advantage via reduced metabolic overhead and greater longevity. Of course, as John notes, not only does this have great relevance for the deep-time history of our species, it is going to be a serious issue for the possibility of future paperback editions of
The Seven Daughters of Eve or
The Real Eve (since they assume neutrality for mtDNA, ergo, it gives us an unbiased phylogenetic map).