Michael E. McCullough University of Miami. Robert Kurzban University of Pennsylvania/Chapman University. Debra Lieberman University of Miami.

Transcription

1 Studying Mechanisms in SBE Research 1 What Would Happen to the Human Sciences if We Took Seriously the Fact that Behavior is Caused by Mental Mechanisms that Evolved to Execute Specific Functions? Michael E. McCullough University of Miami Robert Kurzban University of Pennsylvania/Chapman University Debra Lieberman University of Miami Abstract Functional organization requires explanation. The only known natural causal process that can generate complex functional order is natural selection. This fact is widely appreciated in disciplines that seek to understand non-human behavior and cognition, and in some areas of human psychology (e.g., perception), but in the human social, behavioral, and economic sciences, natural selection s unique role in creating functional organization is generally ignored. As NSF s SBE Directorate advances, the time is ripe to bring the social, behavioral, and economic sciences into conceptual integration not only with other facets of psychology, but with the other life sciences as well. Promoting research that starts with rigorous analyses of the forces that sculpted the human brain, and with models of why highly improbable computational neurocircuitry for a given behavior exists at all, can help to unlock many mysteries of human nature. We posit that a truly interdisciplinary approach one that uses the conceptual tools of evolutionary biology and that integrates computational, developmental, and neuroscientific levels of analyses will help to fulfill the aims of the SBE Directorate, not only in the quest for discovering human nature, but also in identifying how a brain sculpted by ancient forces might address modern challenges.

2 Studying Mechanisms in SBE Research 2 For the human social sciences to realize their full potential for producing scientific insights about the causes of human social behavior, we believe that researchers must be properly equipped and incentivized to apply the conceptual tools of functional-evolutionary analyses to the behaviors that they study. The promise of a functional-evolutionary approach is no less than mapping the contents of the human mind, the functions of the evolved mechanisms that reside within it, and the influences of those evolved mechanisms on the important behaviors with which NSF s SBE Directorate concerns itself. The peril of ignoring such a functional approach is continued fractionation within the social, behavioral, and economic sciences, continued isolation from the biological sciences, and deeply flawed characterizations of human nature and human potential. Scientists Who Study Sensation, Perception, and Basic Regulatory Functions Already Acknowledge the Existence of Specialized Psychological Mechanisms Within the domains of the human sciences that address basic sensory, perceptual, and physiological processes, it is widely accepted that mechanisms reside within the human nervous system that were designed by natural selection and that are specialized to execute specific functions. In these domains, scientists acknowledge that the same force of natural selection that produced specialized psychological mechanisms in the minds of non-human animals also produced them in humans. Such mechanisms include specializations for vision (including subsidiary specializations for color vision, motion detection, object recognition, etc.), for sexual responses, for balance and coordination, for taste and smell, for maintaining body temperature, heart rate, and water balance, for fever, for hearing the sounds emitted by rainforest animals, for sensing chemicals to help neonates locate milk, for learning, perceiving, and producing language, for fast acquisition of fear responses to snakes, for building aversions to foods that caused food poisoning, for motivating individuals to eat, drink, and sleep, and so on. There are two reasons for confidence that such mechanisms exist in the human nervous system. The first is that problems such as finding milk (for infants), locating potential sources of food (or predators) in a rainforest environment, learning to fear snakes, or learning to avoid contaminated food would have been stern selection pressures acting upon the bodies and minds of our ancestors. These selection pressures would have strongly favored, through the operation of natural selection upon genetic variation within populations, the glacially slow, gene-by-gene assembly of neural systems designed to implement these functions. The second reason and the reason that is more relevant for how social scientists actually do their work is that the empirical data regarding these behavioral phenomena (namely, the efficiency, specificity, and elegance with which these effects are produced by the structures that produce them) makes it vanishingly improbable that these phenomena are anything other than the functional output of the structures that produce them. Indeed, for scientists who study sensation, perception, and basic physiological processes such as those listed above, it is virtually impossible to understand the topics of study without appealing to the concepts of function, mechanism, and design. Social, Behavioral, and Economic Scientists Have a Harder Time Recognizing Human Behavior as the Output of Specialized Psychological Adaptations

3 Studying Mechanisms in SBE Research 3 In contrast, many intellectual obstacles have prevented SBE scientists in domains that are less closely linked to sensation, perception, and basic physiological processes from recognizing that the processes that they study are also produced by fine-tuned, highly specialized circuits, and that those processes can also be illumined through the rigorous application of a functional-evolutionary analysis. At various times, and to varying degrees, these intellectual obstacles have included centuries-old dichotomies (e.g., nature vs. nurture, biological vs. cultural, innate vs. learned), compelling folk intuitions about the operation of the mind, ideological resistance to biological approaches within the human sciences, and the lack of appreciation of how natural selection simultaneously generates a species-typical psychological architecture and widespread cultural variability. Biologists who study analogous behaviors in non-human animals have faced no such intellectual impediments. As a result, they have been free to follow the theory of evolution by natural selection to its inevitable conclusion: That mechanisms must exist in the nervous systems of non-human animals that are responsible for generating their behavior, including very human-seeming behaviors such as choice, decision-making, trust, cooperation, punishment, consumption, joining groups, leaving groups, evaluating the abilities and attributes of other individuals, advertising one s desirable qualities for potential mates or allies, caring for offspring, resuming positive social relations with individuals following conflict, withdrawing effort from tasks that are not paying off, intimidating rivals, learning from other individuals, signaling one s submissiveness to leaders, saving one s skin, saving oneself for the best possible mate, and saving for a rainy day. The fact that biologists have been free to think functionally about the causes of these behaviors means that their science has progressed. Hypotheses can be generated about real mechanisms that might exist, somewhere, in the nervous systems of the members of a species, and then those hypotheses can be compared against the data. If the hypotheses do not fit the data, so much the worse for the hypothesis, but not for the pursuit itself: The behavior must be produced by a mechanism, and that mechanism must be in there, somewhere. Can the same be said of the human social sciences? Are they actually progressing? Or are they, instead, awash in theories that can usefully accommodate a few local facts, but which rely on explanatory constructs that do not and indeed, could not exist because natural selection could not possibly create them? Even Though Many Behaviors are By-Products of Evolved Mental Mechanisms, Understanding the Causes of Those Behaviors Proceeds from a Functional Analysis At present, science knows of only one natural explanation for organized functional complexity, and that is natural selection. Absent an alternative, it is as true as anything else in science that natural selection is the causal antecedent of the organized mechanisms that generate behavior. The only mechanisms humans have, therefore, are mechanisms that have an evolved function. Nevertheless, not all behavioral phenomena are functional in the biological sense. Rather, many animal behaviors (including human behaviors) are no doubt by-products caused by mechanisms designed to implement other functions. Moths tendencies to fly into candle flames do not result from flame-seeking mechanisms. Whales and dolphins tendencies to beach themselves are not produced by beaching

4 Studying Mechanisms in SBE Research 4 mechanisms. Baboons tendencies to raid human garbage in search of food do not result from dumpster-diving mechanisms. Humans sexual responses to pornography are not generated by pornography-response mechanisms. How can we be so certain? Because (a) natural selection gives rise only to complex designs that (on average) produce behaviors that raised their bearers fitness (as is certainly not the case with flying into flames and beaching); and (b) the creation of complex design requires many thousands of generations (so natural selection would not have had time to create adaptations around recent environmental conditions such as garbage dumpsters and pornography). Likewise, humans do not have mechanisms whose function is to detect dishonest buyers and sellers in Internet auctions, to help them make good decisions in national elections, to help them sift through conflicting evidence about global warming, to motivate them to donate anonymously to charities, or to learn mechanical engineering, linear algebra, or evolutionary biology. Nevertheless, all of these behaviors are the result of mechanisms that were designed for some function. And indeed, they exist only by virtue of the fact that the details of these mechanisms affected the fitness of the individuals that carried the genes that cause the development of these mechanisms. Identifying the ancestral functions of the mechanisms that generate these interesting social and economic behaviors as by-products is still the only reliable way to accurately characterize the causes of those behaviors. To discover the causes of the social and economic behaviors that concern the SBE Directorate, therefore, researchers must start with models of evolved function. There is a deceptively simple but inflexible truth here: The mechanisms responsible for generating behavior must exist somewhere in neural tissue, courtesy of natural selection, and if we know what those mechanisms were designed for, then we can derive correct explanatory models for the behaviors that interest us. The importance of this claim for the behavioral and social sciences cannot be overstated. In contrast, theorizing that implicates mechanisms that could not possibly exist (for example, mechanisms for completely anonymous giving to strangers, mechanisms for maximizing hedonic experience, or even generic and underspecified motivations for self-protection or reward-seeking) may have intuitive appeal, and may even enjoy some success at predicting variance in behavior, but explanations on the basis of non-existent mechanisms are nevertheless guaranteed to be wrong. Functional-evolutionary theorizing can give rise to incorrect hypotheses, too, of course, but when those hypotheses are wrong, we can at least know that a plausible hypothesis has been rejected rather than one that was impossible from the outset. No reputable scientist today would venture to claim that behavior is produced by a soul or by the interactions of four humors. These ideas have disappeared from social science texts and have found their rightful places within texts on the history of social science. We look forward to a day when research in the social, behavioral, and economic sciences is informed by theorizing that explains behavior in terms of evolved mental mechanisms that stand a chance of existing, somewhere in the central nervous systems of living human beings. The only reliable method that science is likely to have for explaining behavior in these terms is to start with a design analysis that invokes naturally selected mental mechanisms and their interactions as its explanans. Any other mode of explanation is guaranteed to be incorrect, and perhaps worse for science, is guaranteed to deter progress by creating an air of certainty that disarms healthy scientific skepticism and intellectual curiosity.

5 Studying Mechanisms in SBE Research 5 We recommend three initiatives that can help to bring functional-evolutionary theorizing more squarely into the human sciences that interest the SBE Directorate: 1. We recommend educational initiatives at all points in the educational pipeline from primary to post-doctoral that can teach current and future researchers the logic of modern evolutionaryfunctional analysis. These educational initiatives should also illustrate how functional-evolutionary theorizing enables scientists to build bridges between observed behavioral traits, the selection pressures that gave rise to the gene-by-gene assembly over evolutionary time of neurological systems that produce those behaviors, the computational logic upon which those neurocognitive mechanisms operate, and how those mechanisms are assembled during development. 2. We recommend that the SBE Directorate encourage research proposals that involve multidisciplinary teams including evolutionary biologists, evolutionary anthropologists, or evolutionary psychologists who work with brain scientists, cognitive scientists, and others to identify (a) specific selection pressures that humans recurrently faced while our species was evolving; (b) the sorts of cognitive mechanisms that might have arisen in response to those selection pressures; (c) the computational processes that well-designed mechanisms for responding to those selection pressures should be designed to implement; and (d) the physical systems that embody those mechanisms. Research projects that incorporate these elements have the potential to link the science of human behavior outward to the other biological and life sciences, downward into the brain, and upward into the evolutionary forces that might be responsible for creating such mechanisms in the first place. 3. The SBE directorate should consider a bold funding initiative to jump-start a bona fide, interdisciplinary evolutionary science of human behavior. Such research, of course, is well under way in some circles, but as the world s largest funder of basic research into human behavior, NSF is in the unique position of steering an entire field through the priorities it establishes for funding. What, for instance, would happen to the human social sciences if, over the next 10 years, NSF encouraged social, behavioral, and economic scientists to identify 100 evolved mental mechanisms that we use to navigate our social and economic lives? The human sciences would be forever transformed. References for Further Reading Pinker, S. (1997). How the mind works. New York: Norton. Tooby, J., & Cosmides, L. (1992). Psychological foundations of culture. In J. Barkow, L. Cosmides & J. Tooby (Eds.), The adapted mind: Evolutionary psychology and the generation of culture (pp ). New York: Oxford University Press. Williams, G. C. (1966). Adaptation and natural selection: A critique of some current evolutionary thought. Princeton, NJ: Princeton University Press.

6 Studying Mechanisms in SBE Research 6 License This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. To view a copy of this license, visit or send a letter to Creative Commons, 171 Second Street, Suite 300, San Francisco, California, 94105, USA. Metadata: <a rel="license" href=" alt="creative Commons License" style="border-width:0" src=" /></a><br /><span xmlns:dc=" property="dc:title"> What Would Happen to the Human Sciences if We Took Seriously the Fact that Behavior is Caused by Mental Mechanisms that Evolved to Execute Specific Functions?</span> by <span xmlns:cc=" property="cc:attributionname">michael E. McCullough, Robert Kurzban, Debra Lieberman</span> is licensed under a <a rel="license" href=" Commons Attribution- NonCommercial-ShareAlike 3.0 Unported License</a>.