Whether more dispensable genes evolve faster than less dispensable ones¹ is a contentious issue^{2, 3, 4}. Comparing yeast and worm genes, Hirsh and Fraser³ observe a gradual tendency for less dispensable genes (those that reduce the growth rate of yeast when knocked out) to have lower rates of protein evolution. Here we repeat their analysis using larger data sets and find no evidence that dispensability explains the variation in rates of protein evolution. Although Hirsh and Fraser provide a model to show why their result is to be expected, our analysis suggests that their model, which assumes among other things that no substitution is advantageous, cannot be generally applied.

1. Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK
2. Department of Plant Taxonomy and Ecology, Eötvös University, Pázmány Péter Sétány 1/C, 1117 Budapest, Hungary

Correspondence to: Laurence D. Hurst¹ e-mail: Email: l.d.hurst@bath.ac.uk