All genes mutate at random, even those confering an adaptive advantage Jacques van Helden, Aix-Marseille Université 28 August 2012 Excellent summary of interesting results regarding a fascinating biological question. A detail though: the following sentence is misleading, because it gives the impressions that mutations affect genes at different rates depending on their adaptive value: "Receptor genes duplicate at random and the duplicated gene, unless it confers an adaptive advantage, then mutates at random. " A duplicated gene that confers an adaptive advantage mutates at the same rate as a non-adaptive duplicated gene. The relative frequencies of observed mutations in adaptive and non-adaptive genes will only occur afterwards, as an effect of natural selection. This might seem a detail, but it is important to avoid such confusion, specially because this kind of reviews is addressed to a relatively broad audience, which might include non-biologists. Competing interests None.