Professor Petrie theorised that since genetic mutations can occur anywhere in the genome, some will affect the ‘DNA repair kit’ possessed by all cells. As a result, some individuals have less efficient repair kits, resulting in greater variation in their DNA as damage does unrepaired.
Although unrepaired DNA is generally harmful – causing tissue to degenerate or develop cancers – it is useful in some parts of the genome, such as those parts resposible for disease defence where variation can help in the resistance to disease. It has long been known that greater variation of DNA in the disease defending regions makes it more likely that an individual can resist attacks by bacteria and viruses.
Using a computer model to map the spread of genes in a population, Professor Petrie demonstrated that the tendency towards reduction in genetic diversity caused by sexual selection is outweighed by the maintenance in greater genetic diversity generated by mutations affecting DNA repair.
I haven’t read the paper…and the press release sounds kind of garbled. I guess the results here are suggesting that polymorphism at the disease resistence loci (e.g., MHC) is so important that DNA repair mechanisms can’t get too good. A byproduct of this is variance in the mutational load across the population. I suppose this sort of answer to “why we’re not all hot” is like the answer to why we’re not all parthenogenetic.