Glossary of "Evolution (4th ed.)" by Futuyma & Kirkpatrick (2017)
- The ratio of the number of nonsynonymous substitutions per nonsynonymous site(dN) and the number of synonymous substitutions per synonymous site (dS). Values of this ratio smaller than one are consistent with purifying selection, while values greater than one suggest the action of positive selection.
- Futuyma, D. J. & Kirkpatrick, M. 2017. Evolution, 4th ed. -xviii + 602 pp. Sinauer Associates, Inc., Sunderland.