evolgen

Do They Even Read the Literature?

I present for you an example of inferring a bit too much from inappropriate data. This isn’t quite the same as making claims about demography based on 100 nucleotides from 6 individuals. But it’s not much better given that this example is from a study of extant organisms. Abstracts to clarify what the hell I’m talking about are below the fold.

Exhibit A comes from a paper on human demography and mitochondrial DNA. Here is the abstract:

Human mitochondrial DNA (mtDNA) studies have entered a new phase since the blossoming of complete genome analyses. Sequencing complete mtDNAs is more expensive and more labour intensive than restriction analysis or simply sequencing the control region of the molecule. But the efforts are paying off, as the phylogenetic resolution of the mtDNA tree has been greatly improved, and, in turn, phylogeographic interpretations can be given correspondingly greater precision in terms of the timing and direction of human dispersals. Therefore, despite mtDNA being only a fraction of our total genome, the deciphering of its evolution is profoundly changing our perception about how modern humans spread across our planet. Here we illustrate the phylogeographic approach with two case studies: the initial dispersal out of Africa, and the colonization of Europe.

Cool stuff, eh? That mtDNA is really neat. Or not, as Exhibit B points out:

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 ~3000 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.

So much for the power of mtDNA.

Comments

  1. #1 AJR
    June 10, 2006

    Is it fair to criticize them for not having read something that was only published 2 months before their paper? Presumably their paper was already accepted and they may not even have seen the paper critical of mtDNA studies… Besides, this doesn’t mean mtDNA is useless (I didn’t read these papers and you can only tell so much from an abstract so it’s hard to judge).

  2. #2 RPM
    June 10, 2006

    I don’t expect the authors of the first paper to have read the second paper prior to submitting their review. However, they paint a far too rosy picture of the power of mtDNA. They should know better. Because of the lack of recombination (or extremely minimal recombination) on the mtDNA molecule, it essentially evolves as a single gene (something we have known for a long time). For the authors to claim that mtDNA will reveal amazing insights into demography (for any species) is absurd.