Comment on “Additive Genetic Breeding Values Correlate with the Load of Partially Deleterious Mutations”

An article published in May 2010 in the journal Science appeared to have answered the enigmatic evolutionary question of how individual genetic differences are being maintained in the face of (natural and sexual) selection. Data from a sophisticated breeding experiment with seed beetles suggested that individuals carrying 'good genes' were carrying fewer recessive mutations. Such mutations are normally masked from view, but in inbred individuals they can have severe negative effects. From this finding, they concluded that genetic variation is being maintained by a constant influx of new mutations, both deleterious and beneficial. However, Dr. Erik Postma, a researcher at the Institute of Evolutionary Biology and Environmental Studies, University of Zurich, shows in a Technical Comment in response to this paper (published September 2 in Science), that the association they find is an artefact stemming from an incorrect assumption underlying their analysis. When analysed correctly, there is no such relationship, suggesting that mechanisms other than mutations may in fact be much more important for the maintenance of genetic variation.