Pronunciation: (mī"krō-ev"u-lOO'shun or, esp. Brit., -ē"vu-), [key]
1. evolutionary change involving the gradual accumulation of mutations leading to new varieties within a species.
2. minor evolutionary change observed over a short period of time.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.