BEHAVIORAL AND BRAIN SCIENCES (2002) 25, 489–553 Printed in the United States of America

Adaptationism – how to carry out an exaptationist program1

Paul W. Andrews, Steven W. Gangestad, and Dan Matthews Department of Psychology, University of New Mexico, Albuquerque, NM 87131. {pandrews; sgangest; danda}@unm.edu

Abstract: is a research strategy that seeks to identify and the specific selective forces that drove their evolu- tion in past environments. Since the mid-1970s, paleontologist Stephen J. Gould and have been critical of adaptationism, especially as applied toward understanding behavior and cognition. Perhaps the most prominent criticism they made was that adaptationist explanations were analogous to Rudyard Kipling’s Just So Stories (outlandish explanations for questions such as how the elephant got its trunk). Since storytelling (through the generation of hypotheses and the making of inferences) is an inherent part of science, the criticism refers to the acceptance of stories without sufficient empirical evidence. In particular, Gould, Lewontin, and their colleagues argue that adaptationists often use inappropriate evidentiary standards for identifying adaptations and their func- tions, and that they often fail to consider alternative hypotheses to . Playing prominently in both of these criticisms are the concepts of constraint, , and . In this article we discuss the standards of evidence that could be used to identify adap- tations and when and how they may be appropriately used. Moreover, building an empirical case that certain features of a trait are best explained by exaptation, spandrel, or constraint requires demonstrating that the trait’s features cannot be better accounted for by adap- tationist hypotheses. Thus, we argue that the testing of alternatives requires the consideration, testing, and systematic rejection of adap- tationist hypotheses. Where possible, we illustrate our points with examples taken from human behavior and cognition.

Keywords: adaptation; ADHD; brain allometry; constraint; epistemology; ; exaptation; female orgasm; opti- mization; special design; waist-hip ratio (WHR)

1. Introduction Jay Gould and geneticist Richard Lewontin (e.g., Gould & Lewontin 1979; Lewontin 1978; 1979). Perhaps the most In the past decade, evolutionary psychology has emerged as prominent criticism they made was that the explanations an important theoretical perspective in psychology. Evolu- that adaptationists gave for traits were analogous to Rud- tionary psychology is a methodologically rich field that could yard Kipling’s Just So Stories (outlandish explanations for be applied to a variety of interesting questions (e.g., phylo- questions such as how the elephant got its trunk). Of genetic analysis of psychological and behavioral traits). One course, the criticism is not against storytelling in science per approach receiving much attention in recent years pre- se. The generation of hypotheses and the making of infer- dominantly involves the application of adaptationism to ences is an inherent part of science. Rather, the criticism understanding the and nature of human psycho- refers to the acceptance of stories without sufficient em- logical design (Barkow et al. 1992; Buss 1995; Ciba Foun- pirical evidence. Gould, Lewontin, and their colleagues dation 1997; Pinker 1997a). Adaptationism, as a research have made two important epistemological criticisms of the strategy, seeks to identify adaptations and to elucid