Jordan's rule
Jordan's rule
[′jȯrd·ənz ‚rül] (evolution)
The rule that organisms which are closely related tend to occupy adjacent rather than identical or distant ranges.
(vertebrate zoology)
The rule that fishes in areas of low temperatures tend to have more vertebrae than those in warmer waters.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.