Nature Reviews Genetics 12, 157–166 (2011)

In figure 1a of the above article, the evolutionary strata (S1–S5) on the human X chromosome were incorrectly labelled. The figure showed the strata in the order S1 to S5, with S1 adjacent to the pseudoautosomal region. The order should be reversed (S5 to S1), with S5 adjacent to the pseudoautosomal region instead. The figure has been amended accordingly, and the corrected article is available at The author apologizes for this error.