Wednesday, February 08, 2006
STEPHEN JAY GOULD AND RICHARD C. LEWONTIN
REPUBLISHED FROM THE ORIGINAL WITH THE KIND PERMISSION OF THE ROYAL SOCIETY OF LONDON: GOULD, S. J. AND LEWONTIN, R. C., 'THE SPANDRELS OF SAN MARCO AND THE PANGLOSSIAN PARADIGM: A CRITIQUE OF THE ADAPTATIONIST PROGRAMME,' PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON, SERIES B, VOL. 205, NO. 1161 (1979), PP. 581-598.
An adaptationist programme has dominated evolutionary thought in england and the united states during the past forty years. It is based on faith in the power of natural selection as an optimizing agent. It proceeds by breaking an organism into unitary 'traits' and proposing an adaptive story for each considered separately. Trade-offs among competing selective demands exert the only brake upon perfection; nonoptimality is thereby rendered as a result of adaptation as well. We criticize this approach and attempt to reassert a competing notion (long popular in continental europe) that organisms must be analyzed as integrated wholes, with baupl�ne so constrained by phyletic heritage, pathways of development, and general architecture that the constraints themselves become more interesting and more important in delimiting pathways of change than the selective force that may mediate change when it occurs. We fault the adaptationist programme for its failure to distinguish current utility from reasons for origin (male tyrannosaurs may have used their diminutive front legs to titillate female partners, but this will not explain why they got so small); for its unwillingness to consider alternatives to adaptive stories; for its reliance upon plausibility alone as a criterion for accepting speculative tales; and for its failure to consider adequately such competing themes as random fixation of alleles, production of nonadaptive structures by developmental correlation with selected features (allometry, pleiotropy, material compensation, mechanically forced correlation), the separability of adaptation and selection, multiple adaptive peaks, and current utility as an epiphenomenon of nonadaptive structures. We support darwin's own pluralistic approach to identifying the agents of evolutionary change."