A new study challenges the current belief of a high human male:female mutation ratio.

A recent comparison of a DNA region that was transposed from the X to the Y chromosome 3-4 million years ago, with the same region on the X chromosome showed only a slight excess of mutant changes on the Y chromosome. This translates to an estimate of 1.7 for the ratio of the male to female mutation rate, much less than the average 5.1 of previous studies. The authors argue that this throws doubt not only on higher male mutation rates in human ancestry, but also on the standard assumption of a high male:female ratio in contemporary human populations. Clearly, more studies are needed to clear up this discrepancy in the ancestral rates, but I believe that the high contemporary male:female ratio for base substitutions is too well established to be overthrown by even a very good evolutionary study.