Ridley, Mark. 1996. Evolution, Second Edition. Blackwell Science, Cambridge MA. ISBN 0-86542-495-0. The one I use. See especially sec. 13.1, "Natural selection is the only known explanation for adaptation" Bill Shear Department of Biology Hampden-Sydney College Hampden-Sydney VA 23943 (804)223-6172 FAX (804)223-6374 email<bills at hsc.edu>