Men are thought to have a higher mutation rate than women and the male-to-female mutation ratio (the 'alpha' value) in primates has been estimated at around 4-6. This estimation has recently been challenged, and it has been suggested that the alpha ratio may be as low as 1.7. In the April 11 Nature, Makova and Li provide evidence supporting the higher estimates (Nature 2002, 416:624-626). They sequenced over 10 kilobases of genomic DNA from a non-coding region of the Y chromosome and a homologous region on chromosome 3 in humans and apes (including bonobo, gorilla, siamang and gibbon). They came up with an alpha value of 5.25, confirming the higher earlier estimations and supporting the hypothesis of strong male-driven evolution of hominids. They suggest that ancient polymorphisms could lead to reduced estimates when comparing closely related species.