Behavioral and Brain Sciences, 25, 527-528

Commentary on Andrews, Gangestad, and Matthews (2002), "Adaptationism: How to Carry Out an Exaptationist Program"

The Evidentiary Standard of Special Design is a Little Bit Like Heaven

Mark Schaller
Department of Psychology
University of British Columbia
2136 West Mall
Vancouver BC V6T 1Z4




Abstract:  Adaptationist explanations for well-known phenomena are of limited value to psychological science. To be truly useful, evolutionary psychological research programs must produce novel discoveries about contemporary cognitive and behavioral processes. The concept of special design is especially useful. Even if special design cannot be convincingly demonstrated, rigorous attempts to meet this evidentiary standard can produce novel scientific contributions.


It's easy to be a critic, and hard work to be a good one. Criticisms of adaptationism are a dime a dozen, but many critics just wave vaguely at other concepts that may offer alternative explanations. When adaptationist logic is applied to the psychological sciences (in the field of evolutionary psychology) the same sorts of criticisms often arise. That's not very useful. Useful scientific critiques don't just stipulate that there might be alternative explanations. They specify actual alternative explanations, defend them with evidence, and promote deeper scientific understanding of evolution and its consequences.

It's also easy to be an adaptationist, and hard work to be a good one. Adaptationist explanations for psychological phenomena are a dime a dozen. But useful research programs in evolutionary psychology do more than just generate adaptationist explanations for psychological phenomena. They consider plausible alternative explanations, address them with evidence, and promote deeper scientific understanding of evolution and its consequences.

That's not easy to do. For reasons both logical and psychological, it is difficult to convince a skeptical audience about the veracity of any one explanation for the origin of a psychological phenomenon; and it's even more difficult to convince them about the veracity of any one evolutionary explanation (Conway & Schaller, 2002).

There's another problem too that evolutionary psychologists face when trying to convince others about the value of their enterprise. The problem stems from the fact that evolutionary psychology bridges two different scientific cultures. Evolutionary psychological explanations must impress two different audiences with different objectives.

On the one hand, there's the audience of evolutionary biologists, a set of scientists whose first order of business is to inquire into the evolutionary processes that influence the features of populations. These folks may get very excited by debates about adaptations, exaptations, and spandrels. They are, after all, professionally interested in the past.

On the other hand, there's the audience of psychologists, a set of scientists whose first order of business is to inquire into the cognitive processes that influence the actions of individuals. These folks may be unimpressed by adaptationist explanations for readily- apparent psychological phenomena. ("Okay, so we're likely to help relatives more than strangers? I already knew that. And older men tend to like younger women? I knew that too. So what?") Nor are many psychologists excited by debates about different kinds of evolutionary origins. Psychologists aren't professionally interested in the past; they are professionally interested in the present, so that they can better predict the future.

This is why adaptationist explanations for psychological phenomena meet with different objections from different kinds of scientists. Some evolutionists may object because alternative evolutionary explanations can't be ruled out (and so an adaptationist explanation might simply be wrong). Psychologists object--or don't care at all-- because these explanations are simply explanations. If an evolutionary explanation (no matter how true) generates no novel predictions about the way the mind works, then the typical psychologist shrugs, "So what?"

Of course, evolutionary psychological research programs can lead to more than mere explanation. This is often overlooked by critics, and--more unfortunately--by many enthusiasts as well. Far too many folks are far too happy to merely invent evolutionary explanations for psychological phenomena that we know already to occur. Some of these explanations may be right. But so what? Explanations about the past contribute meaningfully to the objectives of psychological science only when these explanations lead to novel discoveries about the way the mind works right here, right now.

This is where the concept of special design comes in especially handy. When one speculates that a specific psychological process emerged as an adaptation that facilitated some specific functional outcome, one opens the door to a bunch of additional implications-- implications about subtle cues that may 'trigger' the operation of that process, and about non-obvious constraints operating on that process. These implications are translatable into hypotheses that can be tested and, if supported, may reveal brand-new discoveries about the here-and-now.

For instance, in the realm of helping behavior, the logic of inclusive fitness leads not only to the obvious hypothesis that we help kin more than non-kin, but also to more interesting hypotheses specifying additional variables that moderate this effect (Burnstein, Crandall, & Kitayama, 1994).

Within the realm of interpersonal relationships, adaptationist logic leads to some obvious hypotheses, but also to additional hypotheses specifying subtle deviations from the obvious. As men get older they prefer women who are comparatively younger, yes, but teenage boys prefer older women; and this interesting exception to the rule is predicted from the same logic as the rule itself (Kenrick, Gabrielidis, Keefe, & Cornelius, 1996). Then there's the hypothesis that women not only prefer the smell of symmetrical men, but that they show this preference especially when they're ovulating (Gangestad & Thornhill, 1998). No one encounters those findings and says "So what, I knew that already."

Psychological inquiry into human prejudice processes also benefits from adaptationist principles. Rigorous application of these principles has yielded a number of novel hypotheses and consequent discoveries about the specific features in others that elicit prejudicial responses, the specific forms that these prejudices take, and the specific domains and contexts in which these prejudices are most likely to occur (Kurzban & Leary, 2001; Neuberg, Smith & Asher, 2000; Schaller, 2003).

These and other highly-specified findings are not so easily explained by alternative explanations that imply more generalized consequences. But that's not the main reason they are compelling to a psychological audience. For these folks, these findings are compelling specifically because they tell us something that we didn't already know.

These considerations make me think that the evidentiary standard of special design is a little bit like Heaven. As an atheist, I figure that no matter how hard folks work to get to Heaven, they won't make it. But that's okay; I'm glad they're trying if it motivates them to be better people. I'm also skeptical that evolutionary psychologists can convincingly rule out non- adaptationist explanations for human psychological phenomena. No matter how hard one tries to meet that onerous standard of special design, some critics just won't be convinced. But that's okay. By trying hard to meet that standard, we are more likely to generate novel predictions, discover new phenomena, and make useful contributions to science.



Burnstein, E., Crandall, C., & Kitayama, S. (1994). Some neo- Darwinian decision rules for altruism: Weighing cues for inclusive fitness as a function of the biological importance of the decision. Journal of Personality and Social Psychology 67: 773-789.

Conway, L. G., III, & Schaller, M. (2002). On the verifiability of evolutionary psychological theories: An analysis of the psychology of scientific persuasion. Personality and Social Psychology Review 6: 152-166.

Gangestad, S. W., & Thornhill, R. (1998). Menstrual cycle variation in women's preferences for the scent of symmetrical men. Proceedings of the Royal Society of London B 265: 727-733.

Kenrick, D. T., Gabrielidis, C., Keefe, R. C., & Cornelius, J. (1996). Adolescents' age preferences for dating partners: Support for an evolutionary model of life-history strategies. Child Development 67: 1499-1511.

Kurzban, R., & Leary, M. R. (2001). Evolutionary origins of stigmatization: The functions of social exclusion. Psychological Bulletin 127: 187-208.

Neuberg, S. L., Smith, D. M., & Asher, T. (2000). Why people stigmatize: Toward a biocultural framework. In The social psychology of stigma, ed. T. Heatherton, R. Kleck, J. G. Hull, & M. Hebl (pp. 31-61). New York: Guilford Press.

Schaller, M. (2003). Ancestral environments and motivated social perception: Goal-like blasts from the evolutionary past. In Motivated social perception, ed. S. J. Spencer, S. Fein, M. P. Zanna, & J. M. Olson (pp. 215-231). Mahwah NJ: Lawrence Erlbaum Associates.