quote:
With regard to the apparent deficiency of polymorphisms observed at some loci, the observation is significant because of the number of apparent changes (base substitutions) that have occurred in these loci. Lack of polymorphism implies that, of many possible versions of the gene that did occur, only one was 'tolerable' for that lineage. Strong evidence for selection driving the fixation, otherwise where are all the other variants of the gene that had to come into existence at some point?
The lack of polymorphism does not indicate anything about mutations that occurred but that are not seen as polymorphisms. It is evidence for a selective sweep, in which a mutation at one site brings to fixation any nearby alleles on the particular chromosome on which the favorable mutation occurred.
I also want to digest this paper for a while -- there are some surprising features in their results.