Glossary of "Evolution (4th ed.)" by Futuyma & Kirkpatrick (2017)
- Also called active trend. A prolonged shift in the mean of a character among the species in a clade owing to more frequent changes within species in one direction than the other. In a passive trend, changes in both directions would be equally likely, but are constrained by a boundary in one direction.
- Futuyma, D. J. & Kirkpatrick, M. 2017. Evolution, 4th ed. -xviii + 602 pp. Sinauer Associates, Inc., Sunderland.