J. theor. Biof. (1983) 101, 211-224 On the Problem of Stasis in Organismal Evolution DAVID B. WAKE Museum of Vertebrate Zoology, University of California, Berkeley, California 94720, U.S.A. GERHARD ROTH Department of Biology, University of Bremen, 2800 Bremen 33, West Germany AND MARVALEE H. WAKE Department of Zoology and Museum of Vertebrate Zoology, University of California, Berkeley, California 94720, U.S.A. (Received 15 June 1982) One of the most challenging problems in evolutionary biology is morpho- logical stasis-the maintenance of a standard morphology over vast periods of time during which much environmental change has taken place. We review empirical data for one well studied group of vertebrates, salaman- ders of the family Plethodontidae. Despite much evolution at the level of allozymes, proteins such as albumin, and DNA, morphological evolution has been slow, and has been concentrated in relatively short spans of time. The dominant theme has been morphological stasis. An important con- tributing factor appears to be plasticity-behavioral, physiological, and developmental-which allows organisms to compensate environmental, and even genetic, perturbations without having to change morphologically. Organisms are self-produced and self-maintained systems, and we argue that the best measure of evolutionary adaptation is the persistence of this autopoietic system. Internal dynamics of the organism determine what change will occur and how it is to be expressed. Stable systems can be established which transcend species borders, and the fossil record offers no evidence with regard to speciation rates, or the relationship of speciation events to morphological evolution. We urge that more emphasis be placed on the organism in evolutionary studies. Introduction The concepts of fitness and adaptation are deeply entrenched within modern evolutionary theory. Nonetheless, widespread discontent prevails con- cerning these central concepts, though evolutionary biology is generally 211 0022-5193/83/060211+14$03.00/0 @ 1983 Academic Press Inc. (London) Ltd.