| American Psychologist |
| June 1999 Vol. 54,
No. 6, 443-445 |
We thank the nine commentators for their thoughtful reactions to our article "Adaptations, Exaptations, and Spandrels" ( Buss, Haselton, Shackelford, Bleske, & Wakefield, 1998 ). Several offer useful suggestions for new directions for empirical research ( Roney, 1999 , this issue; Scher, 1999 , this issue), conceptual elaborations ( Hatcher, 1999 , this issue), and an extended set of important references ( Jerison, 1999 , this issue). Roney's (1999 ) commentary is especially important, and we endorse his points fully–testing evolutionary psychological hypotheses requires documenting "special design." Furthermore, we agree with Roney's proposed integration with cognitive science and note that evolutionary psychology is taking steps in this direction (see Cosmides & Tooby, 1994 ).
The commentators raise a number of key issues that require clarification. Evolutionary psychology generates an astonishing number of misunderstandings ( Buss, 1999 ). It violates cherished notions about human nature, such as the belief that humans are blank slates on which culture and socialization write their scripts. It threatens scientists who worry about intellectual territorial invasion, and it creates concerns about misuse for pernicious political purposes. Some just wish it would go away. As Lady Ashley, a Darwin contemporary, commented when she first heard about the theory of evolution by selection, "Let's hope that it's not true; but if it is true, let's hope that it doesn't become widely known." Below we address the issues the commentators raise and thereby attempt to allay some of these concerns.
Several commentators worry about "genetic reductionism," but nowhere in our article ( Buss et al., 1998 ) did we argue for such reductionism. Evolutionary psychology provides a truly interactionist framework, as we outlined in our article. Current behavior is a function of evolved mechanisms combined with environmental input; without environmental input, clearly there would be no behavior. As we explained in "Adaptations, Exaptations, and Spandrels," psychological mechanisms require environmental input at each stage of development. Moreover, existing mechanisms evolved precisely because they interacted with features of the ancestral environment in particular ways–ways that led to their propagation more than coexisting alternative designs. Attempts to characterize evolutionary psychology as "genetic determinism" wildly miss the central tenets of evolutionary psychology.
Consider the hypothesis that sexual jealousy is a psychological mechanism that evolved to combat intrasexual threats and mate defections (e.g., Buss, Larsen, & Westen, 1996 ). The mechanism is activated only when a person encounters social input, such as interest in one's mate from rivals or cues to infidelity ( Shackelford & Buss, 1997 ). Proposed design features include sensitivity to the social context of marriages, such as sex-linked components of mate value ( Buss & Shackelford, 1997 ), as well as sex differences in the weighting given to cues to sexual versus emotional infidelity, corresponding to the different adaptive problems ancestral men and women confronted ( Buss et al., 1999 ). This is not genetic determinism; it's a precisely specified form of interactionism.
Several commentators present arguments for plasticity and adaptability , and these words have intuitive resonance. Clearly humans learn, grow, develop new patterns, and adjust to changing circumstances. Clearly the human brain can do things it was not "designed" to do, including reading, writing, pecking on typewriters, and surfing the Internet. Evolutionary psychology does not propose a rigid, robotic set of "instincts" that manifest themselves invariantly in behavior, nor does it propose that existing psychological mechanisms cannot be coopted for new uses during a person's life.
In our view, however, words like plasticity can be misleading and often obscure more than they clarify. Plasticity connotes lack of form, a shapeless mass that can be molded and fashioned into nearly anything, but surely that's not an accurate description of the human brain. No amount of higher education will cause a human brain to suddenly develop the echolocation abilities of bats, the elaborate olfactory sensitivity of dogs, or the web-spinning ability of spiders. Without specifying more precisely which features of the environment the brain responds to and in which predictable ways it responds, invocations of plasticity or adaptability constitute theoretical hand waving.
According to the central tenets of evolutionary psychology, human behavior is indeed flexible, but our intuitions mislead us about the source of that flexibility. Flexibility is not achieved because the human brain is a formless plastic lump or because the brain is a general information processor ( Tooby & Cosmides, 1992 ). Flexibility is achieved because of the elaborate suite of specific evolved mechanisms humans possess, activated in designed sequences in different combinations from an astonishingly complex menu. Flexibility is achieved because of the tremendous complexity, precision, and number of evolved psychological mechanisms. Invoking plasticity to explain this precision and complexity obscures more than it clarifies.
Some argue that we cannot rewind the tape of human evolutionary history and so cannot make scientific inferences about the selective events of the past. But if this were true, then there could be no science of cosmology, no studies of stellar evolution, and no geological theory of continental drift, nor could there be any science of evolutionary biology, archeology, or paleontology. Should cosmologists, geologists, archeologists, paleontologists, evolutionary biologists, and evolutionary psychologists pack their bags and call it quits?
Many scientific disciplines require making inferences about the past. Although such inferences are obviously fraught with conceptual and empirical difficulties, legitimate scientific standards can be imposed. Three-degree black body radiation, observations of the expansion of galaxies, studies of critical mass, and other sources of data permit reasonable inferences about events surrounding the origin of the universe billions of years ago. In evolutionary psychology, a wide variety of data sources are available, including archeological records, data from traditional hunter—gatherer cultures, and skull and skeletal finds.
Perhaps even more important, the current design of evolved mechanisms provides a window into the past ( Tooby & Cosmides, 1992 ). That humans tend to develop fears of snakes, spiders, heights, darkness, and strangers more than fears of cars or electrical outlets reveals something important about the "hostile forces of nature" our ancestors confronted. The design features of sexual jealousy, to take another example, provide windows for viewing the likely infidelity and defection threats faced by human ancestors struggling to hold on to a long-term mate. The current design of a mechanism provides a promising working hypothesis about the fitness- relevant features of our past evolutionary environment.
Some worry that accepting the science of evolutionary psychology carries abhorrent ethical consequences, such as exoneration of personal responsibility. If it can be demonstrated conclusively that men have evolved a desire for sexual variety, will this provide an excuse for men to be unfaithful? Perhaps some men will argue, "I couldn't help playing around; my evolved psychology made me do it!"
Evolutionary psychology is a science that describes and explains; it does not prescribe. It is a fallacy to argue that just because something exists, it ought to exist. Humans try to eliminate many things that are deemed natural, including certain parasites and diseases. Many laws are created specifically to deter people from doing things that they might naturally be inclined to do if there were not such laws.
Those who object to evolutionary psychology because of a fear of pernicious ethical implications often commit another fallacy–a fallacy that conflates what they want to exist with what does exist ( Buss, 1994 ). Some don't want it to be true that the sexes differ in their evolved sexual psychology, for example, and this leads some to reject theories and evidence that suggest that they do. Clearly, committing this fallacy is the road to obscurantism. The science of evolutionary psychology is designed to explain and understand human nature. If it threatens to discover some unpleasant truths about human nature, are we really better off with blinders?
Evolution by selection remains the only viable scientific theory that can explain the origin and complex functional design of human nature. From this perspective, the issue is not "evolutionary or not evolutionary," but rather, "what is the design of human nature that evolution by selection has created?" We can go the route of Lady Ashley and hope that it doesn't become widely known. We can attempt to suppress its discoveries. Or we can face the fact that humans evolved, have been subjected to the principles of evolution by selection, and have a distinctive human nature. The goal of evolutionary psychology is to use all of the conceptual and empirical tools we now have available to elucidate where we came from, the selective forces that fashioned us, and the mechanisms of mind that define who we are.
Correspondence may be addressed to
Electronic mail may be
sent to dbuss@psy.utexas.edu