=== Glossary of Evolution (2nd ed.) by Futuyma (2009)
- A process of genetic change in a population whereby, as a result of natural selection, the average state of a character becomes improved with reference to a specific function, or whereby a population is thought to have become better suited to some feature of its environment. Also, an adaptation: a feature that has become prevalent in a population because of a selective advantage conveyed by that feature in the improvement in some function.
Glossary of Campbell Biology (7th ed.) by Campbell & Reece (2005)
Glossary of Campbell Biology (8th ed.) by Campbell et al. (2008)
Glossary of The Cell (5th ed.) by Alberts et al. (2008)
- Alberts, B., Johnson, A., Lewis, J. Raff, M., Roberts, K. & Walter P. 2008. Molecular Biology of the Cell, 5th ed. -xxxiii + 1268 pp. Garland Science, New York.
- Campbell, N. A. & Reece, J. B. 2005. Biology, 7th ed. -xl + 1231 pp. Pearson Benjamin Cummings, San Francisco.
- Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V. & Jackson, R. B. 2008. Biology, 8th ed. -xlvi + 1267 pp. Pearson Benjamin Cummings, San Francisco.