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Current Directions in Psychological Science http://cdp.sagepub.com/ Mutually Responsive Orientation Between Mothers and Their Young Children: A Context for the Early Development of Conscience Grazyna Kochanska Current Directions in Psychological Science 2002 11: 191 DOI: 10.1111/1467-8721.00198 The online version of this article can be found at: http://cdp.sagepub.com/content/11/6/191 Published by: http://www.sagepublications.com On behalf of: Association for Psychological Science Additional services and information for Current Directions in Psychological Science can be found at: Email Alerts: http://cdp.sagepub.com/cgi/alerts Subscriptions: http://cdp.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsReprints.nav Permissions: http://www.sagepub.com/journalsPermissions.nav Downloaded from cdp.sagepub.com at OHIO STATE UNIVERSITY LIBRARY on December 27, 2010 CURRENT DIRECTIONS IN PSYCHOLOGICAL SCIENCE These basic questions are central to any evolutionary approach. Psychologists who do not like the simplicity of the answers currently coming out of evolutionary psychology should make an effort to improve them, to broaden its intellectual horizon, because all of psychology would stand to gain from a more enlightened evolutionary psychology. Recommended Reading de Waal, F.B.M. (1999). The end of nature versus nurture. Scientific American, 281, 94–99. de Waal, F.B.M. (2001). The ape and the sushi master: Cultural reflections by a primatologist. New York: Basic Books. Mayr, E. (2001). What evolution is. New York: Basic Books. Zimmer, C. (2001). Evolution: The triumph of an idea. New York: Harper Collins. Acknowledgments— I thank Allison Berger and Virginia Holt for providing the transcript of my 2001 Focus on Science Plenary Address, which was presented at the annual meeting of the American Psychological Association in San Francisco and was on the topic of this essay. I am also grateful to Mauricio Papini and Scott Lilienfeld for comments on previous versions of the manuscript. more: Johns Hopkins University Press. (Original work published 1982) de Waal, F.B.M. (2000, April 2). Survival of the rapist [Review of the book A natural history of rape: Biological bases of sexual coercion]. New York Times Book Review, pp. 24–25. Dobzhansky, T. (1973). Nothing in biology makes sense except in the light of evolution. American Biology Teacher, 35, 125–129. Gauthier, I., & Tarr, M.J. (1997). Becoming a “Greeble” expert: Exploring mechanisms for face recognition. Vision Research, 37, 1673–1682. Notes 1. Address correspondence to Frans B.M. de Waal, Living Links, Yerkes Primate Research Center, Emory University, 954 N. Gatewood Rd., Atlanta, GA 30322. 2. Theory of mind means that one understands the mental states of others (a capacity that may be limited to humans and apes). References Daly, M., & Wilson, M. (1988). Homicide . Hawthorne, NY: Aldine de Gruyter. de Waal, F.B.M. (1996). Good natured: The origins of right and wrong in humans and other animals. Cambridge, MA: Harvard University Press. de Waal, F.B.M. (1998). Chimpanzee politics. Balti- McDougall, W. (1908). An introduction to social psychology. New York: Putnam. Muscarella, F., & Cunningham, M.R. (1996). The evolutionary significance and social perception of male pattern baldness and facial hair. Ethology & Sociobiology, 17, 99–117. Panksepp, J., & Panksepp, J.B. (2000). The seven sins of evolutionary psychology. Evolution and Cognition, 6, 108–131. Staats, A.W. (1991). Unified positivism and unification psychology: Fad or new field? American Psychologist, 46, 899–912. Thornhill, R., & Palmer, C.T. (2000). A natural history of rape: Biological bases of sexual coercion. Cambridge, MA: MIT Press. Tooby, J., & Cosmides, L. (1992). The psychological foundations of culture. In J. Barkow, L. Cosmides, & J. Tooby (Eds.), The adapted mind: Evolutionary psychology and the generation of culture (pp. 19–136). New York: Oxford University Press. Williams, G. (1966). Adaptation and natural selection. Princeton, NJ: Princeton University Press. Wilson, E.O. (1998). Consilience: The unity of knowledge. New York: Knopf. Mutually Responsive Orientation Between Mothers and Their Young Children: A Context for the Early Development of Conscience dinal beneficial effects of MRO for early development of conscience have been replicated across studies, for a broad range of developmental periods from infancy through early school age, and using a wide variety of behavioral, emotional, and cognitive measures of conscience in the laboratory, at home, and in school. These findings highlight the importance of the early parent-child relationship for subsequent moral development. Grazyna Kochanska1 Department of Psychology, University of Iowa, Iowa City, Iowa Abstract Some parent-child dyads establish a mutually responsive orientation (MRO), a relationship that is close, mutually binding, cooperative, and affectively positive. Such relationships have two main characteristics—mutual responsiveness and shared positive affect—and they foster the 191 development of conscience in young children. Children growing up with parents who are responsive to their needs and whose interactions are infused with happy emotions adopt a willing, responsive stance toward parental influence and become eager to embrace parental values and standards for behavior. The concurrent and longitu- Keywords relationships; mutuality; conscience How do young children become aware of rules, values, and standards of behavior accepted within their Copyright © 2002 American Psychological Society Downloaded from cdp.sagepub.com at OHIO STATE UNIVERSITY LIBRARY on December 27, 2010 192 VOLUME 11, NUMBER 6, DECEMBER 2002 families and cultures? How do they gradually come to internalize those values and make them their own? Why do some children adopt societal norms wholeheartedly and with ease, and become conscientious citizens, whereas others do not? The emergence of an individual conscience, a reliable internal guidance system that regulates conduct without the need for external control, is the endpoint of the process of integrating a child into a broader network of values. How this process works continues to be debated as one of the perennial and central issues in human socialization (Grusec, 1997). Research on conscience was once dominated by a cognitive approach, focused on children’s abstract understanding of societal rules, measured by their ability to reason about hypothetical moral dilemmas. Moral development was seen as a product of cognitive maturation, aided by peer interactions, but fundamentally unrelated to parental influence. In contrast, other theories acknowledged parental contributions. Parents and other socializing agents were seen as critical in several versions of learning theory. Those approaches emphasized the importance of parental discipline and modeling as instruments that modify and shape children’s behavior. Somewhat later, attributional theories underscored the importance of children’s perceptions of parental discipline, and revealed surprising, often paradoxical effects of salient parental rewards and punishments. More recently, many scholars have come to appreciate an approach grounded in psychoanalytic and neo-psychoanalytic theories. Although Freud’s views on the early development of conscience as linked to the Oedipus or Electra complex have long been discarded, his general emphasis on the role of early emotions and early relationships in emerging morality has proven insightful. That approach has been strongly reinvigo- rated and modernized by John Bowlby and the burgeoning research on attachment. From that perspective, moral emotions, moral conduct, and moral thought are all components of an internal guidance system, or conscience, whose foundations are established in early childhood in the context of socialization in the family. The early parent-child relationship, which encompasses but is not limited to control and discipline, can substantially foster or undermine that process (Emde, Biringen, Clyman, & Oppenheim, 1991). THE RELATIONSHIP PERSPECTIVE: MUTUALLY RESPONSIVE ORIENTATION In 1951, Robert Sears argued for a shift in psychological research from studying individuals to studying dyads. Over the past two or three decades, the science of relationships has blossomed in personality, social, and developmental psychology (Collins & Laursen, 1999; Reis, Collins, & Berscheid, 2000). Several scholars have proposed that when relationship partners—whether two adults or a parent and a child— are responsive and attuned to each other, are mutually supportive, and enjoy being together, they form an internal model of their relationship as a cooperative enterprise, and develop an eager, receptive stance toward each other’s influence and a compelling sense of obligation to willingly comply with the other. For example, Clark (1984) referred to “communal relationships” in adults as contexts in which the partners are invested in each other’s well-being, are empathic and responsive to each other, and experience an internal sense of mutual obligation. In developmental research, those resurging perspectives afford a productive vantage point for exploring social development. Socialization is seen as a process jointly constructed by parents and children over time (Collins & Laursen, 1999; Collins, Maccoby, Steinberg, Hetherington, & Bornstein, 2000; Maccoby, 1999; Reis et al., 2000). Maccoby (1999) referred to parent-child mutuality as a positive socialization force that engenders a spirit of cooperation in the child. Attachment scholars believe that children raised in a loving, responsive manner become eager to cooperate with their caregivers and to embrace their values. To describe such relationships between parents and children, my colleagues and I have proposed a construct of mutually responsive orientation (MRO). MRO is a positive, close, mutually binding, and cooperative relationship, which encompasses two components: responsiveness and shared positive affect . Responsiveness refers to the parent’s and the child’s willing, sensitive, supportive, and developmentally appropriate response to one another’s signals of distress, unhappiness, needs, bids for attention, or attempts to exert influence. Shared positive affect refers to the “good times” shared by the parent and the child—pleasurable, harmonious, smoothly flowing interactions infused with positive emotions experienced by both. We further proposed that children who grow up in mutually responsive dyads, compared with those who do not, become more eager to embrace their parents’ values and more likely to develop a strong conscience. Their eager stance to embrace parental values reflects an internal sense of obligation to respond positively to parental influence, and emerges from a history of mutually gratifying, mutually accommodating experiences. A child who has developed a mutually responsive relationship with the parent comes to trust the parent and to expect that the parent will be responsive and supportive; Published by Blackwell Publishing Inc. Downloaded from cdp.sagepub.com at OHIO STATE UNIVERSITY LIBRARY on December 27, 2010 193 CURRENT DIRECTIONS IN PSYCHOLOGICAL SCIENCE at the same time, the child comes to feel motivated to cooperate willingly with the parent, to embrace the parent’s values, and to adopt parental standards for behavior and make them his or her own. In this view, the parent-child relationship influences the child’s conscience mainly through a gradually evolving shared working model of the relationship as a mutually cooperative enterprise rather than through the cumulative history of parental discipline as the instrument of behavior modification. MOTHER-CHILD MRO AND CHILDREN’S CONSCIENCE: EMPIRICAL EVIDENCE In two large studies, we measured the qualities of the motherchild relationship and the child’s emerging conscience for more than 200 mother-child dyads. To assess the strength of MRO for the individual dyads, we observed the mothers and children interacting in multiple lengthy, naturalistic yet carefully scripted contexts at home and in the laboratory. The situations we observed included caregiving routines, preparing and eating meals, playing, relaxing, and doing household chores. We coded each mother’s responsiveness to her child’s numerous signals of needs, signs of physical or emotional distress or discomfort, bids for attention, and social overtures. We also assessed shared positive affect by coding the flow of emotion expression for both the mother and the child over the course of each interaction, focusing particularly on the times when they both displayed positive emotion. We obtained these measures repeatedly, following the same families over a period of several years. In the individual dyads, the degree of MRO was significantly con- sistent across separate sessions close in time, and significantly stable over several years. This indicates that our observational markers captured a robust quality of the relationships that unfolded along a fairly stable dyadic trajectory. Using a broad variety of laboratory paradigms, we also observed rich manifestations of the young children’s conscience: moral emotions, moral conduct, and moral cognition. These assessments took place at many points in the children’s development—starting in their 2nd year and continuing until early school age. The children’s moral emotions, including guilt, discomfort, concern, and empathy, were observed when they were led to believe that they had violated a standard of conduct, or when they witnessed others’ distress. While they were unsupervised, either alone or with peers, their moral conduct was assessed in many types of situations in which they faced strong temptations to break various rules and were coaxed to violate standards of behavior. Their moral cognition was measured by presenting them with age-appropriate, hypothetical moral dilemmas and asking them to express their thoughts and feelings about rules and transgressions, and consider moral decisions. We also asked their mothers and teachers to evaluate the children’s moral emotions and conduct displayed in environments outside the laboratory—at home and at school. Both studies supported the view that children who grow up in a context of a highly mutually responsive relationship with their mothers develop strong consciences (Kochanska, 1997; Kochanska, Forman, & Coy, 1999; Kochanska & Murray, 2000). The strength of the replicated findings was striking, given the broad range of the children’s ages and the wide variety of conscience measures used. In both studies, the links between MRO and the development of conscience were both concurrent and longitudinal. The concurrent links were found for both toddlers and preschoolers. The longitudinal findings were robust: MRO in infancy predicted conscience development in the 2nd year, and MRO in toddlerhood predicted children’s conscience at preschool age and again at early school age. The history of MRO in the first 2 years predicted conscience at age 5. In short, the beneficial effect of MRO on the development of conscience was evident across diverse measures of conscience involving emotions, conduct, and cognition. It was also evident whether conscience was assessed by observations in the laboratory or reports from mothers and teachers. These results have been replicated by other researchers (Laible & Thompson, 2000). HOW DOES MRO EXERT ITS IMPACT? What causal mechanisms may be responsible for these well-established empirical findings? Using statistical approaches (sequences of multiple regressions, as well as structural equations modeling, or SEM) to analyze the causal factors that accounted for the associations in our data, we determined that MRO exerts its influence through at least two mechanisms. The first mechanism involves promoting the child’s positive mood. Early MRO between the parent and the child contributes to the child’s positive, happy disposition, and that, in turn, increases his or her broad eagerness to behave prosocially. This finding is consistent with a large body of research in social and developmental psychology (Eisenberg & Fabes, 1998). Adults and children who are in a positive mood have often been Copyright © 2002 American Psychological Society Downloaded from cdp.sagepub.com at OHIO STATE UNIVERSITY LIBRARY on December 27, 2010 194 VOLUME 11, NUMBER 6, DECEMBER 2002 found to be more prosocial, altruistic, cooperative, rule abiding, and socially responsive than those who are in neutral or negative moods. The second mechanism involves promoting the child’s responsive stance toward parental influence. We have found that in playlike teaching situations, children in mutually responsive relationships are attuned to their mothers and eagerly follow their lead (Forman & Kochanska, 2001; Kochanska et al., 1999). In discipline situations, they show what we called committed compliance—willing, eager, wholehearted cooperation with the parent (Kochanska, Coy, & Murray, 2001). Such a generalized responsive stance may be an intermediate step between simple cooperation with the parent and genuine internalization of parental rules, evident even in the parent’s absence. We believe it reflects the child’s emerging working model of a cooperative, reciprocal, mutually accommodating relationship in which partners naturally do things for one another without abrogating their autonomy. FUTURE RESEARCH DIRECTIONS MRO and Qualities of Individuals It takes two to develop dyadic MRO. Although the relationship between a parent and child—like any relationship—is more than a simple sum of their characteristics, those characteristics may nevertheless foster or impede the formation of MRO. Recent advances in research on the role of genetics in behavior and on the biological foundations of children’s temperament are beginning to be reflected in scientific work in what has been traditionally conceived as the domain of relationships. For example, Deater- Deckard and O’Connor (2000), studying identical and fraternal twins, and biological and adoptive siblings, found that parent-child MRO was driven, in part, by the child’s genetically based qualities. In addition, a child’s biologically based traits, such as being prone to anger or joy, or being hard or easy to soothe, may facilitate or undermine the evolution of the child’s relationships within particular dyads. Being responsive to and having enjoyable interactions with a child may be more challenging if the child is temperamentally difficult than if he or she is easygoing and mellow. Mothers’ traits, some also biologically based, may be important as well. We have found that the more empathic mothers are, the better able they are to form MRO with their children (Kochanska, 1997). A large body of research indicates that depression and high levels of negative emotion in mothers reduce their responsiveness and positive behavior when interacting with their young children. More complex interplay between biological and relationship factors also deserves future research attention. Our findings indicate that MRO may be particularly beneficial for children with certain temperaments, particularly fearless, thrill-seeking children whose behavior is not easily modified by actual or anticipated punishments and threats. Other interactions between temperament and relationships are also possible. MRO as a Developmentally Changing System A mutually responsive relationship between a parent and an infant differs from a mutually responsive relationship between a parent and a preschooler, or between a parent and an adolescent. The contexts and currency of par- ent-child interactions change. In infancy, those contexts include mostly the contexts of caregiving, play, and daily routines, and the currency of exchange is often nonverbal. Gradually, the contexts expand to include parent-child discussions of events and ideas, and the exchanges are increasingly verbal (Laible & Thompson, 2000). The child’s and the parent’s relative contributions to the relationship change over time, and so do their cognitive representations, perceptions, and expectations of the relationship and of each other. Psychologists’ understanding of the child’s side of MRO lags considerably behind their understanding of the parent’s side of MRO. How MRO can be assessed in a manner that is developmentally sensitive and yet captures stable qualities of the parent-child dyad over time is one of the future challenges. MRO and Internal Representations In research to date, MRO has been inferred from parents’ and children’s observed behavior and affect during interactions. This outer layer, however, only partially captures the essence of a relationship. Scholars studying relationships have adopted Bowlby’s premise that, over time, the parent and the child gradually form inner representations, or internal working models, of their relationship (Collins & Laursen, 1999). Those evolving models include generalized memories of each other’s behavior, implicit beliefs and feelings about each other and the relationship, and a sense of what the relationship is like and what to expect from one another. Those generalized products of an individual’s experience serve to organize and bias his or her future information processing, behavior, and emotions. In the case of MRO, the parent’s and Published by Blackwell Publishing Inc. Downloaded from cdp.sagepub.com at OHIO STATE UNIVERSITY LIBRARY on December 27, 2010 CURRENT DIRECTIONS IN PSYCHOLOGICAL SCIENCE child’s internal models entail mutual cooperation and implicit reciprocity, and the child’s internal model is thought to underlie his or her willingness to embrace parental rules. Those inner representations, however, are difficult to access and to study. To develop sensitive yet rigorous methodologies that will provide insights into the representational aspect of MRO is an important future challenge. MRO and the Family System The relationship between a parent and child is itself nested in a network of family relationships. The importance of studying development in the context of the entire family system has been increasingly acknowledged. In particular, future research should study mother-child and father-child MRO, both separately and as a triadic interconnected system. More generally, family-level variables such as stress, conflict, support, and affective ambience may be significant dimensions of the context in which mutually responsive relationships with the child may flourish or fail. Recommended Reading Collins, W.A., & Laursen, B. (Eds.). (1999). (See References) Kochanska, G. (1997). (See References) Kochanska, G., & Murray, K.T. (2000). (See References) Acknowledgments— This research has been sponsored by grants from the National Institute of Mental Health (RO1 MH63096, KO2 MH01446) and National Science Foundation (DBS-9209559, SBR9510863) to the author. I gratefully acknowledge the comments of Nazan Aksan, David Forman, and Robert Siegler, and contributions of numerous students, staff, and the families who participated in the studies. Note 1. Address correspondence to Grazyna Kochanska, Department of Psychology, University of Iowa, Iowa City, IA 52242-1447. References Clark, M.S. (1984). Record keeping in two types of relationships. Journal of Personality and Social Psychology, 47, 549–557. Collins, W.A., & Laursen, B. (Eds.). (1999). Minnesota Symposia on Child Psychology: Vol. 30. Relationships as developmental contexts. Hillsdale, NJ: Erlbaum. Collins, W.A., Maccoby, E.E., Steinberg, L., Hetherington, E.M., & Bornstein, M.H. (2000). Contemporary research on parenting: The case for nature and nurture. American Psychologist, 55, 218–232. Deater-Deckard, K., & O’Connor, T.G. (2000). Parent-child mutuality in early childhood: Two behavioral genetic studies. Developmental Psychology, 36, 561–570. 195 Eisenberg, N., & Fabes, R.A. (1998). Prosocial development. In W. Damon (Series Ed.) & N. Eisenberg (Vol. Ed.), Handbook of child psychology: Vol. 3. Social, emotional, and personality development (pp. 701–778). New York: Wiley. Emde, R.N., Biringen, Z., Clyman, R.B., & Oppenheim, D. (1991). The moral self of infancy: Affective core and procedural knowledge. Developmental Review, 11, 251–270. Forman, D.R., & Kochanska, G. (2001). Viewing imitation as child responsiveness: A link between teaching and discipline domains of socialization. Developmental Psychology, 37, 198–206. Grusec, J.E. (1997). A history of research on parenting strategies and children’s internalization of values. In J.E. Grusec & L. Kuczynski (Eds.), Parenting and children’s internalization of values: A handbook of contemporary theory (pp. 3–22). New York: Wiley. Kochanska, G. (1997). Mutually responsive orientation between mothers and their young children: Implications for early socialization. Child Development, 68, 94–112. Kochanska, G., Coy, K.C., & Murray, K.T. (2001). The development of self-regulation in the first four years of life. Child Development, 72, 1091– 1111. Kochanska, G., Forman, G., & Coy, K.C. (1999). Implications of the mother-child relationship in infancy for socialization in the second year of life. Infant Behavior and Development, 22, 249– 265. Kochanska, G., & Murray, K.T. (2000). Motherchild mutually responsive orientation and conscience development: From toddler to early school age. Child Development, 71, 417–431. Laible, D.J., & Thompson, R.A. (2000). Motherchild discourse, attachment security, shared positive affect, and early conscience development. Child Development, 71, 1424–1440. Maccoby, E.E. (1999). The uniqueness of the parent-child relationship. In W.A. Collins & B. Laursen (Eds.), Minnesota Symposia on Child Psychology: Vol. 30. Relationships as developmental contexts (pp. 157–175). Hillsdale, NJ: Erlbaum. Reis, H.T., Collins, W.A., & Berscheid, E. (2000). Relationships in human behavior and development. Psychological Bulletin, 126, 844–872. Copyright © 2002 American Psychological Society Downloaded from cdp.sagepub.com at OHIO STATE UNIVERSITY LIBRARY on December 27, 2010 Current Directions in Psychological Science http://cdp.sagepub.com/ Ape and Human Cognition : What's the Difference? Michael Tomasello and Esther Herrmann Current Directions in Psychological Science 2010 19: 3 DOI: 10.1177/0963721409359300 The online version of this article can be found at: http://cdp.sagepub.com/content/19/1/3 Published by: http://www.sagepublications.com On behalf of: Association for Psychological Science Additional services and information for Current Directions in Psychological Science can be found at: Email Alerts: http://cdp.sagepub.com/cgi/alerts Subscriptions: http://cdp.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsReprints.nav Permissions: http://www.sagepub.com/journalsPermissions.nav Downloaded from cdp.sagepub.com at Max Planck Society on November 25, 2010 Ape and Human Cognition: What’s the Difference? Current Directions in Psychological Science 19(1) 3-8 ª The Author(s) 2010 Reprints and permission: sagepub.com/journalsPermissions.nav DOI: 10.1177/0963721409359300 http://cdps.sagepub.com Michael Tomasello and Esther Herrmann Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany Abstract Humans share the vast majority of their cognitive skills with other great apes. In addition, however, humans have also evolved a unique suite of cognitive skills and motivations—collectively referred to as shared intentionality—for living collaboratively, learning socially, and exchanging information in cultural groups. Keywords apes, culture, cognition, evolution, cooperation Surely one of the deepest and most important questions in all of the psychological sciences is how human cognition is similar to and different from that of other primates. The main datum is this: Humans seemingly engage in all kinds of cognitive activities that their nearest primate relatives do not, but at the same time there is great variability among different cultural groups. All groups have complex technologies but of very different types; all groups use linguistic and other symbols but in quite different ways; all groups have complex social institutions but very different ones. What this suggests is that human cognition is in some way bound up with human culture. Here we argue that this is indeed the case, and we then try to explain this fact evolutionarily. Similarities in Ape and Human Cognition The five great ape species (orangutans, gorillas, chimpanzees, bonobos, humans) share a common ancestor from about 15 million years ago, with the last three sharing a common ancestor from about 6 million years ago (see Fig. 1 for a picture of chimpanzees). Since great apes are so closely related to one another evolutionarily, it is natural that they share many perceptual, behavioral, and cognitive skills. primates’ cognitive skills for dealing with the physical world almost certainly evolved in the context of foraging for food. As compared with other mammals, primates may face special challenges in locating their daily fare, since ripe fruits are patchy resources that are irregularly distributed in space and time. Other studies suggest that great apes understand their social worlds in basically the same way as humans as well. Like humans, apes live in a world of identifiable individuals with whom they form various kinds of social relationships—for example, in terms of dominance and ‘‘friendship’’—and they recognize the third-party social relationships that other individuals have with one another. Moreover, they go beneath this understanding of social behavior and relationships to understand the goals and perceptions of social partners acting as intentional agents (see Call & Tomasello, 2008, for a review). Apes’ and other primates’ cognitive skills for dealing with the social world evolved mainly in the context of competition with groupmates for valued resources, and primates, as compared with other mammals, live in especially complex social groups (leading to so-called Machiavellian intelligence; Byrne & Whiten, 1988). Great ape cognitive operations Great ape cognitive worlds Many different studies suggest that nonhuman great apes (hereafter great apes) understand the physical world in basically the same way as humans. Like humans, apes live most basically in a world of permanent objects (and categories and quantities of objects) existing in a mentally represented space. Moreover, they understand much about various kinds of events in the world and how these events relate to one another causally (see Tomasello & Call, 1997, for a review). Apes’ and other Great apes also operate on their cognitive worlds in ways very similar to humans. Thus, apes not only perceive and understand things in the immediate here and now but they also recall things Corresponding Author: Michael Tomasello, Max Planck Institute for Evolutionary Anthropology, Department of Developmental and Comparative Psychology, Deutscher Platz 6, D-04103 Leipzig, Germany E-mail: tomas@eva.mpg.de Downloaded from cdp.sagepub.com at Max Planck Society on November 25, 2010 4 Tomasello, Herrmann Fig. 1. Chimpanzees in a social group. they have perceived in the past and anticipate or imagine things that might happen in the future. For example, in a recent study, some great apes used a tool to retrieve food, and when the food was gone they dropped the tool and left. Later, when they returned, more food was there but the necessary tool was not. After only a few repetitions of this procedure, the apes learned to take the tool with them after using it, in anticipation of the next trial when they would need it again (Mulcahy & Call, 2006). Great apes also can make inferences about what one perceived state or event implies about another. For example, in another experiment, great apes were faced with two cups, and they knew that only one of them contained food. They then watched as a human shook one. Not only were they able to infer which one had food when they heard it in there, they were also able to infer which one had food (i.e., the other one) when the shaken cup made no sound. This is a kind of reasoning by exclusion (analogous to disjunctive syllogism in formal logic): (a) the food is in one of the cups; (b) it is not in this one (inferred from lack of sound—causal reasoning); (c) so then it must be in the other one. The apes thus used their knowledge and reasoning to imagine the food in the correct cup (Call, 2004). Apes also can reason about the decision making of other individuals. For instance, in a recent study, human-raised chimpanzees observed a human successfully solving a problem in a particular way. The chimpanzees then either followed that way or not depending on whether their particular circumstances— that is, the obstacles to solving the problem—were the same or different as those that had faced the human demonstrator. They seemingly reasoned about why the human had chosen the behavioral means she had (Buttelmann, Carpenter, Call, & Tomasello, 2007). Differences in Ape and Human Cognition Since humans have brains three times larger than other great apes—and share so many basic cognitive skills with them—it would be natural to assume that humans are just more cognitively sophisticated than apes in a general way. But this is not the case; the situation is much more interesting than that. Downloaded from cdp.sagepub.com at Max Planck Society on November 25, 2010 Ape and Human Cognition 5 An overall comparison In a recent study, Herrmann, Call, Hernández-Lloreda, Hare, and Tomasello (2007) gave an extensive battery of cognitive tasks to large numbers of chimpanzees, orangutans, and 2-year-old human children. The tasks assessed all kinds of cognitive skills for dealing with both the physical and the social world. If what differentiates humans from their nearest primate relatives is simply a greater degree of general intelligence—better skills of perceptual discrimination, larger working memories, more inferencing skills, and so forth—then the children should have differed from the apes uniformly across all the different kinds of tasks. But that was not the case. The finding was that the children were very similar to the apes in their cognitive skills for dealing with space, quantities, and causality; 2-year-olds still have their same basic great-ape skills for dealing with the physical world. But these same 2-year-old children—still preliterate, prenumerical, and preschool—showed much more sophisticated cognitive skills for dealing with the social world in terms of intention-reading, social learning, and communication. So early in ontogeny human infants show some quantitative advantages over apes in social-cognitive skills that they do not show in other cognitive domains. The proposal is that the children’s special social-cognitive skills represent the dawning of a special kind of cultural intelligence evolved for participating in a cultural group. Participating in a cultural group will then enhance all of children’s cognitive skills across the board, including those for dealing with the physical world—as children, for example, imitate others’ tool use, acquire a language and all its conceptual categories, learn mathematical symbols and operations via instruction, and so forth. Children’s special skills of social cognition thus bootstrap their skills of physical cognition by enabling them to collaborate with, communicate with, and learn from others in the cultural group. Evolutionarily, the key difference is that humans have evolved not only social-cognitive skills geared toward competition, but also social-cognitive skills and motivations geared toward complex forms of cooperation—what we call skills and motivations for shared intentionality (Tomasello, Carpenter, Call, Behne, & Moll, 2005). Most important are skills and motivations for shared intentionality in children’s (a) collaboration and communication and (b) cultural learning and transmission. The ability to collaborate and communicate with others in sophisticated, species-unique ways is apparent even in prelinguistic human infants (see Fig. 2). In a recent comparative study, human 1-year-olds and juvenile chimpanzees each engaged in a collaborative task with a human adult. When the adult stopped participating, the chimpanzees simply tried to solve the task alone. The human children, in contrast, employed various forms of communication to try to reengage the adult into the task. The children seemed to understand that the two of them had committed themselves to doing this together and it simply would not do if the adult was shirking her duty. The collaboration was structured by joint goals and joint commitments to one another (Warneken, Chen, & Tomasello, 2006). It is not difficult to see in these simple activities the roots of the kind of collaborative commitments and activities that structure human social institutions, from governments to religions. And the way humans communicate is fundamentally cooperative as well. Humans do not just try to get others to do what they want them to—which is what most animal communication (and much human communication) is about—but they also communicate simply to inform others of things helpfully and to share emotions and attitudes with them freely. Human infants communicate in this cooperative way even before they acquire language, especially with the pointing gesture (Tomasello, Carpenter, & Lizskowski, 2007). Human languages, as the pinnacles of human communication, rely on these cooperative motives as well, but they are also constituted by fundamentally cooperative communicative devices— known as linguistic conventions (or symbols)—whose meanings derive from a kind of cooperative agreement that we will all use them in the same way (Tomasello, 2008). Both collaborative activities with shared goals and cooperative communication using shared symbols are structured by joint attention. This means that as children work together with others or communicate with them, they have a mutual awareness that this is what they are doing: We are both committed to this joint goal; or, we are both focused on this same object together. This creates the possibility of culturally constituted entities that exist because, and only because, everyone in the group believes and acts as if they do—for example, such things as marriage and money and presidents (Searle, 1995). Cultural learning and transmission Collaboration and communication Virtually all of humans’ highest cognitive achievements are not the work of individuals acting alone but rather of individuals collaborating in groups. Other great apes, especially chimpanzees, coordinate their actions with others in a number of complex ways—for example, in capturing small animals and in coalitions and alliances in intragroup conflicts (Muller & Mitani, 2005). But humans collaborate and communicate with one another in especially complex ways that go beyond simple coordination, ending up with such things as complex social institutions structured by joint goals, division of labor, and communicative symbols. All great apes, especially chimpanzees and orangutans, transmit some behaviors and information across generations culturally (Whiten & van Schaik, 2007). But the human way of living depends fundamentally and totally on cultural learning and transmission. In particular, the human way of living depends on processes of cultural evolution in which material and symbolic artifacts and social practices accumulate modifications over time (ratchet up in complexity), such that they have a ‘‘history’’ within the group upon which others can always build (Tomasello, 1999). Much empirical research on social learning and imitation has shown that young children understand and reproduce, to Downloaded from cdp.sagepub.com at Max Planck Society on November 25, 2010 6 Tomasello, Herrmann Fig. 2. Collaboration in young children. a greater extent than other apes, not just the environmental result of others’ actions but also the behavioral and cognitive processes used to produce that result (Whiten, 2005). In addition, other important aspects of cultural learning in humans derive from their special cooperative skills and motivations, and these add to the power of the human cultural ratchet as well. Specifically, adults teach children things intentionally— whereas teaching is not an important dimension in the lives of other great apes, if it exists at all—and teaching is a form of altruistic cooperation (free donation of information). Human children are especially attuned to adults teaching them things (Gergely & Csibra, 2006), and they trust adult instruction implicitly based on their cooperative motives. Indeed, when adults teach them things, children trust this so much they often jump to normative conclusions. Thus, they learn not just that this is how the adult did it, but that this is how it is done— this is how we in this group do it, how it ought to be done. For example, in a recent study, 3-year-old children who witnessed a puppet playing a game in a manner discrepant with the way they had been taught objected strenuously: The puppet was not doing it ‘‘right’’ (Rakoczy, Warneken, & Tomasello, 2008). Such normative judgments derive, almost certainly, from identifying with the group in terms of how ‘‘we’’ do things. And so to complement their special skills of collaborating with others in the moment, human children also come into the world ready to ‘‘collaborate,’’ as it were, with forebears in their culture, by adopting their artifacts, symbols, skills, and practices via imitation and instructed learning. Their cooperative identification with the group leads them to learn not just that this is a useful way to do things to meet individual goals, but it is the ‘‘right’’ way to do things, at least for members of this group. This almost moral dimension makes human cultural learning especially powerful in comparison to that of their closest primate relatives. The Coevolution of Human Culture and Cognition As compared with their nearest great-ape relatives, humans occupy an incredibly wide range of environmental niches Downloaded from cdp.sagepub.com at Max Planck Society on November 25, 2010 Ape and Human Cognition 7 covering almost the entire planet. To deal with everything from the Arctic to the tropics, humans as a species have evolved a highly flexible suite of cognitive skills. But these are not individual cognitive skills that enable individuals to survive alone in the tundra or rain forest, but rather they are social-cognitive skills that enable them to develop, in concert with others in their cultural groups, creative ways of coping with whatever challenges may arise. Humans have not only skills of individual intentional action and cognition but also skills and motivations for sharing intentions and cognition with others. What most clearly distinguishes human cognition from that of other primates, therefore, is their adaptations for functioning in cultural groups. Groups of individuals cooperate together to create artifacts and practices that accumulate improvements (rachet up in complexity) over time, thus creating ever-new cognitive niches (Tomasello, 1999). Children must be equipped to participate in this process during their development by means of species-unique cognitive skills for collaboration, communication, and cultural learning. Humans are thus characterized to an inordinate degree by what has been called niche construction and gene–culture coevolution (Richerson & Boyd, 2005), as the species has evolved cognitive skills and motivations enabling them to function effectively in any one of many different self-built cultural worlds. Some important questions for future research include the following: ! ! ! ! How precisely do children’s skills of collaboration and imitative learning differ from those of other great apes? Do great apes teach? Is human teaching part and parcel of their more cooperative way of communicating, or something different? What are the differences in motivation and emotion that contribute to humans’ special cooperative tendencies and skills? How do humans’ skills of cultural creation and cultural learning differ across cultures—especially those that emerge early in ontogeny? Recommended Reading Call, J., & Tomasello, M. (2008). (See References). A concise review of research on chimpanzee social cognition (theory of mind) over the past 30 years. Herrmann, E., Call, J., Hernández-Lloreda, M., Hare, B., & Tomasello, M. (2007). (See References). Results of the administration of a very large cognitive test battery to large numbers of chimpanzees, orangutans, and 2-year-old human children. Richerson, P.J., & Boyd, R. (2005). (See References). A comprehensive description of research and theory on the nature of human culture in evolutionary context. Tomasello, M., Carpenter, M., Call, J., Behne, T., & Moll, H. (2005). (See References). A theoretical framework for thinking about how skills and motivations of shared intentionality manifest themselves during human ontogeny. Tomasello, M. (2008). (See References). A theoretical account of how cooperative communication, including conventional languages, emerged in human evolution. Declaration of Conflicting Interests The authors declared no potential conflicts of interest with respect to the authorship and/or publication of this article. References Buttelmann, D., Carpenter, M., Call, J., & Tomasello, M. (2007). Enculturated chimpanzees imitate rationally. Developmental Science, 10, F31–38. Byrne, R.W., & Whiten, A. (Eds.). (1988). Machiavellian Intelligence: Social Expertise and the Evolution of Intellect in Monkeys, Apes, and Humans. New York: Oxford University Press. Call, J. (2004). Inferences about the location of food in the great apes (Pan paniscus, Pan troglodytes, Gorilla gorilla, and Pongo pygmaeus). Journal of Comparative Psychology, 118, 232–241. Call, J., & Tomasello, M. (2008). Do chimpanzees have a theory of mind: 30 years later. Trends in Cognitive Science, 12, 187–192. Gergely, G., & Csibra, G. (2006). Sylvia’s recipe: The role of imitation and pedagogy in the transmission of cultural knowledge. In N.J. Enfield, & S.C. Levinson (Eds.), Roots of human sociality: Culture, cognition and interaction (pp. 229–255). Oxford, UK: Berg Press. Herrmann, E., Call, J., Hernández-Lloreda, M., Hare, B., & Tomasello, M. (2007). Humans have evolved specialized skills of social cognition: The cultural intelligence hypothesis. Science, 317, 1360–1366. Mulcahy, N.J., & Call, J. (2006). Apes save tools for future use. Science, 312, 1038–1040. Muller, M.N., & Mitani, J.C. (2005). Conflict and cooperation in wild chimpanzees. Advances in the Study of Behavior, 35, 275–331. Rakoczy, H., Warneken, F., & Tomasello, M. (2008). The sources of normativity: Young children’s awareness of the normative structure of games. Developmental Psychology, 44, 875–881. Richerson, P.J., & Boyd, R. (2005). Not by Genes Alone: How Culture Transformed Human Evolution. Chicago: University of Chicago Press. Searle, J. (1995). The Construction of Social Reality. New York: Free Press. Tomasello, M. (1999). The Cultural Origins of Human Cognition. Cambridge, MA: Harvard University Press. Tomasello, M. (2008). Origins of Human Communication. Cambridge, MA: MIT Press. Tomasello, M., & Call, J. (1997). Primate Cognition. New York: Oxford University Press. Tomasello, M., Carpenter, M., Call, J., Behne, T., & Moll, H. (2005). Understanding and sharing intentions: The origins of cultural cognition. Behavioral and Brain Sciences, 28, 675–691. Downloaded from cdp.sagepub.com at Max Planck Society on November 25, 2010 8 Tomasello, Herrmann Tomasello, M., Carpenter, M., & Lizskowski, U. (2007). A new look at infant pointing. Child Development, 78, 705–722. Warneken, F., Chen, F., & Tomasello, M. (2006). Cooperative activities in young children and chimpanzees. Child Development, 77, 640–663. Whiten, A. (2005). The second inheritance system of chimpanzees and humans. Nature, 437, 52–55. Whiten, A., & van Schaik, C.P. (2007). The evolution of animal ‘cultures’ and social intelligence. Philosophical Transactions of the Royal Society B, 362, 603–620. Downloaded from cdp.sagepub.com at Max Planck Society on November 25, 2010 Current Directions in Psychological Science http://cdp.sagepub.com/ Three Laws of Behavior Genetics and What They Mean Eric Turkheimer Current Directions in Psychological Science 2000 9: 160 DOI: 10.1111/1467-8721.00084 The online version of this article can be found at: http://cdp.sagepub.com/content/9/5/160 Published by: http://www.sagepublications.com On behalf of: Association for Psychological Science Additional services and information for Current Directions in Psychological Science can be found at: Email Alerts: http://cdp.sagepub.com/cgi/alerts Subscriptions: http://cdp.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsReprints.nav Permissions: http://www.sagepub.com/journalsPermissions.nav >> Version of Record - Oct 1, 2000 What is This? Downloaded from cdp.sagepub.com at OhioLink on January 7, 2013 160 VOLUME 9, NUMBER 5, OCTOBER 2000 Three Laws of Behavior Genetics and What They Mean Eric Turkheimer1 to the implications of the genetics of behavior for an understanding of complex human behavior and its development. Department of Psychology, University of Virginia, Charlottesville, Virginia Abstract Behavior genetics has demonstrated that genetic variance is an important component of variation for all behavioral outcomes, but variation among families is not. These results have led some critics of behavior genetics to conclude that heritability is so ubiquitous as to have few consequences for scientific understanding of development, while some behavior genetic partisans have concluded that family environment is not an important cause of developmental outcomes. Both views are incorrect. Genotype is in fact a more systematic source of variability than environment, but for reasons that are methodological rather than substantive. Development is fundamentally nonlinear, interactive, and difficult to control experimentally. Twin studies offer a useful methodological shortcut, but do not show that genes are more fundamental than environments. Keywords genes; environment; development; behavior genetics The nature-nurture debate is over. The bottom line is that everything is heritable, an outcome that has taken all sides of the naturenurture debate by surprise. Irving Gottesman and I have suggested that the universal influence of genes on behavior be enshrined as the first law of behavior genetics (Turkheimer & Gottesman, 1991), and at the risk of naming laws that I can take no credit for discovering, it is worth stating the nearly unanimous results of behavior genetics in a more formal manner. ● First Law. All human behavioral traits are heritable. ● Second Law. The effect of being raised in the same family is smaller than the effect of genes. ● Third Law. A substantial portion of the variation in complex human behavioral traits is not accounted for by the effects of genes or families. It is not my purpose in this brief article to defend these three laws against the many exceptions that might be claimed. The point is that now that the empirical facts are in and no longer a matter of serious controversy, it is time to turn attention to what the three laws mean, Published by Blackwell Publishers Inc. Downloaded from cdp.sagepub.com at OhioLink on January 7, 2013 VARIANCE AND CAUSATION IN BEHAVIORAL DEVELOPMENT If the first two laws are taken literally, they seem to herald a great victory for the nature side of the old debate: Genes matter, families do not. To understand why such views are at best an oversimplification of a complex reality, it is necessary to consider the newest wave of opposition that behavior genetics has generated. These new critics, whose most articulate spokesman is Gilbert Gottlieb (1991, 1992, 1995), claim that the goal of developmental psychology is to specify the actual developmental processes that lead to complex outcomes. In lower animals, whose breeding and environment can be brought under the control of the scientist, it is possible to document such developmental processes in exquisite detail. The critics draw an unfavorable comparison between these detailed animal studies and twin studies of behavior genetics, which produce only statistical conclusions about the relative importance of genes and environment in development. The greatest virtue of the new challenge is that it abandons the CURRENT DIRECTIONS IN PSYCHOLOGICAL SCIENCE implausible environmentalist contention that important aspects of behavior will be without genetic influence. Gottlieb (1992) stated, “The present . . . viewpoint holds that genes are an inextricable component of any developmental system, and thus genes are involved in all traits” (p. 147). Unlike earlier critics who deplored the reductionism they attributed to behavior genetic theories of behavior, the developmental biologists take behavior genetics to task for not being mechanistic enough. Once vilified as the paragon of determinist accounts of human behavior, behavior genetics is now chastised for offering vague and inconclusive models of development (Gottlieb, 1995; Turkheimer, Goldsmith, & Gottesman, 1995), and judged by the standards of developmental psychobiology in lower animals, it is true enough that behavior genetic theories of complex human behavior seem woefully poorly specified. But ultimately the charge is unfair, because there is no equivalent in developmental psychobiology to the behavior genetic study of marital status or school performance. The great preponderance of the exquisite experimental science that goes into animal psychobiology is quite simply impossible to conduct in humans. Human developmental social science is difficult—equally so for the genetically and environmentally inclined—because of the (methodologically vexing, humanistically pleasing) confluence of two conditions: (a) Behavior emerges out of complex, nonlinear developmental processes, and (b) ethical considerations prevent us from bringing most human de- 161 velopmental processes under effective experimental control. Figure 1 is a schematic illustration of the problem. Individual genes (Genes 1, 2, and 3) and their environments (which include other genes) interact to initiate a complex developmental process that determines adult personality. Most characteristic of this process is its interactivity: Subsequent environments to which the organism is exposed depend on its earlier states, and each new environment changes the developmental trajectory, which affects future expression of genes, and so forth. Everything is interactive, in the sense that no arrows proceed uninterrupted from cause to effect; any individual gene or environmental event produces an effect only by interacting with other genes and environments. For the behavior geneticist, Fig. 1. Schematic diagram of contrasting roles of genes and environment in development of personality. One-headed arrows link causes to effects; two-headed arrows indicate correlations. Genes and environments are both causal inputs into an interactive developmental system (represented by the network of arrows in the center of the figure), but because people select and shape their own environments (as represented by lighter one-headed arrows from personality to environments), correlations across the developmental system (dotted two-headed arrows) are easier to detect for genes than for environments. Copyright © 2000 American Psychological Society Downloaded from cdp.sagepub.com at OhioLink on January 7, 2013 162 however, the quasi-experimental gift of genetically identical and nonidentical twins offers a remarkable, if deceptively simple, method to span this daunting interactive complexity. Thanks to the fact that identical twins are on average exactly twice as similar genetically as nonidentical twins, one can use straightforward statistical procedures to estimate the proportion of variability in complex outcomes that is associated with causally distant genes, all the while maintaining a state of near-perfect ignorance about the actual causal processes that connect genes to behavior. This methodological shortcut is not available to rivals of behavior genetics who seek to measure the effects of families on behavior. How similar was my rearing environment to that of my siblings? And how similar was it to the environment of my adopted sibling, if I have one, or to the environment of my biological sibling who was raised by someone else? The apparent victory of nature over nurture suggested by the first two laws is thus seen to be more methodological than substantive. In a world in which there were occasional occurrences of “identical environmental twins,” whose experiences were exactly the same, moment by moment, and another variety who shared exactly (but randomly) 50% of their experiences, environmentalists could reproduce the precision of their rivals, and like the behavior geneticists could measure with great precision the total contribution of the environment while knowing almost nothing about the developmental processes that underlie it. The old-fashioned nature-nurture debate was about whether or not genes influence complex behavioral outcomes, and that question has been decisively answered in the affirmative. The new question is how we can proceed from VOLUME 9, NUMBER 5, OCTOBER 2000 partitioning sources of variance to specifying concrete developmental processes (Turkheimer, 1998), and although critics like Gottlieb are correct that heritability per se has few implications for a scientific understanding of development, they have failed to emphasize two crucial points. First, heritability does have one certain consequence: It is no longer possible to interpret correlations among biologically related family members as prima facie evidence of sociocultural causal mechanisms. If the children of depressed mothers grow up to be depressed themselves, it does not necessarily demonstrate that being raised by a depressed mother is itself depressing. The children might have grown up equally depressed if they had been adopted and raised by different mothers, under the influence of their biological mother’s genes. For every behavior geneticist who continues to report moderate heritabilities as though they were news, there is an environmentalist who reports causally ambiguous correlations between genetically related parents and children. Second, the problem the critics have uncovered extends well beyond behavior genetics: It is a rare environmentalist who has never used statistical methods to predict behavioral outcomes from earlier events, in the hope that the specific developmental mechanisms can be filled in later. The disconnect between the analysis of variance and the analysis of causes, to use Lewontin’s (1974) phrase, is not a proprietary flaw in behavior genetic methodology; in fact, it is the bedrock methodological problem of contemporary social science. NONSHARED ENVIRONMENT AND THE GLOOMY PROSPECT Even after the effects of genes and the shared effects of families Published by Blackwell Publishers Inc. Downloaded from cdp.sagepub.com at OhioLink on January 7, 2013 have been accounted for, around 50% of the differences among siblings is left unexplained. In recent years, scientists interested in the genetics of behavior have come to call this unexplained portion the “nonshared environment.” Although according to the second law shared environment accounts for a small proportion of the variability in behavioral outcomes, according to the third law, nonshared environment usually accounts for a substantial portion. So perhaps the appropriate conclusion is not so much that the family environment does not matter for development, but rather that the part of the family environment that is shared by siblings does not matter. What does matter is the individual environments of children, their peers, and the aspects of their parenting that they do not share. Plomin and Daniels (1987) reviewed evidence of the predominance of nonshared environmental variance and posed a seminal question: Why are children in the same family so different? They proposed that siblings are different because nonshared environmental events are more potent causes of developmental outcomes than the shared environmental variables, like socioeconomic status, that have formed the traditional basis of sociocultural developmental psychology. Plomin and Daniels’s explanation involves a subtle conceptual shift, best described in terms of a distinction between the objective and effective environment (Goldsmith, 1993; Turkheimer & Waldron, 2000). What qualifies an environmental event as nonshared? There are two possibilities. The first is objective: An event is nonshared if it is experienced by only one sibling in a family, regardless of the consequences it produces. The other possibility is effective: An environmental event is nonshared if it makes siblings different CURRENT DIRECTIONS IN PSYCHOLOGICAL SCIENCE rather than similar, regardless of whether it was experienced by one or both of them. Plomin and Daniels’s proposal, then, is that the nonshared environment as an effectively defined variance component can be explained by objectively nonshared environmental events. The question, “Why are children in the same family so different?” is answered, “Because measurable differences in their environments make them that way.” This proposal has been enormously influential, spawning an entire area of empirical inquiry into the consequences of measured environmental differences among siblings. Ironically, that same literature has quite decisively demonstrated that the conjecture is false. A review of 43 studies that measured differences in the environments of siblings and related them to differences in the siblings’ developmental outcomes (Turkheimer & Waldron, 2000) has shown that although upwards of 50% of the variance in behavioral outcomes is accounted for by the effectively defined variance component called nonshared environment, the median percentage accounted for by objectively defined nonshared events is less than 2%. What could be going on? Plomin and Daniels (1987) almost identified the answer to this question, but dismissed it as too pessimistic: One gloomy prospect is that the salient environment might be unsystematic, idiosyncratic, or serendipitous events such as accidents, illnesses, or other traumas . . . . Such capricious events, however, are likely to prove a dead end for research. More interesting heuristically are possible systematic sources of differences between families. (p. 8) The gloomy prospect is true. Nonshared environmental variability predominates not because of the systematic effects of environmental events that are not shared among siblings, but rather because of the unsystematic effects of all environmental events, compounded by the equally unsystematic processes that expose us to environmental events in the first place (Turkheimer & Gottesman, 1996). A model of nonshared variability based on the gloomy prospect is radically different from the Plomin model based on systematic consequences of environmental differences among siblings. Most important, the two models suggest very different prospects for a genetically informed developmental psychology. Again and again, Plomin and his colleagues have emphasized that the importance of nonshared environment implies that it is time to abandon shared environmental variables as possible explanations of developmental outcomes. And although modern environmentalists might not miss coarse measures like socioeconomic status, it is quite another thing to give up on the causal efficaciousness of normal families, as Scarr (1992), Rowe (1994), and Harris (1998) have urged. If, however, nonshared environmental variability in outcome is the result of the unsystematic consequences of both shared and nonshared environmental events, the field faces formidable methodological problems—Plomin and Daniels’s gloomy prospect—but need not conclude that aspects of families children share with siblings are of no causal importance. CONCLUSION: ANTICIPATING THE GENOME PROJECT It is now possible for behavior genetics to move beyond statistical analyses of differences between identical and nonidentical twins and identify individual genes that are related to behavioral outcomes. Copyright © 2000 American Psychological Society Downloaded from cdp.sagepub.com at OhioLink on January 7, 2013 163 What should we expect from this endeavor? Behavior geneticists anticipate vindication: At long last, statistical variance components will be rooted in the actual causal consequences of actual genes. Critics of behavior genetics expect the opposite, pointing to the repeated failures to replicate associations between genes and behavior as evidence of the shaky theoretical underpinnings of which they have so long complained. There is an interesting parallel between the search for individual genes that influence behavior and the failed attempt to specify the nonshared environment in terms of measured environmental variables. In each case, investigators began with statistically reliable but causally vague sources of variance, and set out to discover the actual causal processes that produced them. The quest for the nonshared environment, as we have seen, got stuck in the gloomy prospect. Although individual environmental events influence outcomes in the most general sense, they do not do so in a systematic way. One can detect their effects only by accumulating them statistically, using twins or adoptees. If the underlying causal structure of human development is highly complex, as illustrated in Figure 1, the relatively simple statistical procedures employed by developmental psychologists, geneticists, and environmentalists alike are being badly misapplied. But misapplied statistical procedures still produce what appear to be results. Small relations would still be found between predictors and outcomes, but the underlying complex causal processes would cause the apparent results to be small, and to change unpredictably from one experiment to the next. So individual investigators would obtain “results,” which would then fail to replicate and accumulate into a coherent theory because the 164 simple statistical model did not fit the complex developmental process to which it was being applied. Much social science conducted in the shadow of the gloomy prospect has exactly this flavor (e.g., Meehl, 1978). The gloomy prospect looms larger for the genome project than is generally acknowledged. The question is not whether there are correlations to be found between individual genes and complex behavior—of course there are—but instead whether there are domains of genetic causation in which the gloomy prospect does not prevail, allowing the little bits of correlational evidence to cohere into replicable and cumulative genetic models of development. My own prediction is that such domains will prove rare indeed, and that the likelihood of discovering them will be inversely related to the complexity of the behavior under study. Finally, it must be remembered that the gloomy prospect is gloomy only from the point of view of the working social scientist. Although frustrated developmental psychologists may be tempted to favor methodologically tractable heuris- VOLUME 9, NUMBER 5, OCTOBER 2000 tics over chaotic psychological reality, it is a devil’s choice: In the long run, the gloomy prospect always wins, and no one would want to live in a world where it did not. Psychology is at least one good paradigm shift away from an empirical answer to the gloomy prospect, but the philosophical response is becoming clear: The additive effect of genes may constitute what is predictable about human development, but what is predictable about human development is also what is least interesting about it. The gloomy prospect isn’t. Recommended Reading Gottlieb, G. (1992). (See References) Lewontin, R.C. (1974). (See References) Meehl, P.E. (1978). (See References) Plomin, R., & Daniels, D. (1987). (See References) Note 1. Address correspondence to Eric Turkheimer, Department of Psychology, 102 Gilmer Hall, P.O. Box 400400, University of Virginia, Charlottesville, VA 22904-4400; e-mail: turkheimer@ virginia.edu. Published by Blackwell Publishers Inc. Downloaded from cdp.sagepub.com at OhioLink on January 7, 2013 References Goldsmith, H. (1993). Nature-nurture issues in the behavioral genetic context: Overcoming barriers to communication. In R. Plomin & G. McClearn (Eds.), Nature, nurture and psychology (pp. 325–339). Washington, DC: American Psychological Association. Gottlieb, G. (1991). Experiential canalization of behavioral development: Theory. Developmental Psychology, 27, 4–13. Gottlieb, G. (1992). Individual development and evolution. New York: Oxford University Press. Gottlieb, G. (1995). Some conceptual deficiencies in “developmental” behavior genetics. Human Development, 38, 131–141. Harris, J.R. (1998). The nurture assumption: Why children turn out the way they do. New York: Free Press. Lewontin, R.C. (1974). The analysis of variance and the analysis of causes. American Journal of Human Genetics, 26, 400–411. Meehl, P.E. (1978). Theoretical risks and tabular asterisks: Sir Karl, Sir Ronald, and the slow progress of soft psychology. Journal of Consulting and Clinical Psychology, 46, 806–834. Plomin, R., & Daniels, D. (1987). Why are children in the same family so different from one another? Behavioral and Brain Sciences, 10, 1–60. Rowe, D.C. (1994). The limits of family influence: Genes, experience, and behavior. New York: Guilford Press. Scarr, S. (1992). Developmental theories for the 1990s: Development and individual differences. Child Development, 63, 1–19. Turkheimer, E. (1998). Heritability and biological explanation. Psychological Review, 105, 782–791. Turkheimer, E., Goldsmith, H.H., & Gottesman, I.I. (1995). Commentary. Human Development, 38, 142–153. Turkheimer, E., & Gottesman, I.I. (1991). Is H2 = 0 a null hypothesis anymore? Behavioral and Brain Sciences, 14, 410–411. Turkheimer, E., & Gottesman, I.I. (1996). Simulating the dynamics of genes and environment in development. Development and Psychopathology, 8, 667–677. Turkheimer, E., & Waldron, M.C. (2000). Nonshared environment: A theoretical, methodological, and quantitative review. Psychological Bulletin, 126, 78–108. Current Directions in Psychological Science http://cdp.sagepub.com/ Genetic and Environmental Influences on Cognition Across Development and Context Elliot M. Tucker-Drob, Daniel A. Briley and K. Paige Harden Current Directions in Psychological Science 2013 22: 349 DOI: 10.1177/0963721413485087 The online version of this article can be found at: http://cdp.sagepub.com/content/22/5/349 Published by: http://www.sagepublications.com On behalf of: Association for Psychological Science Additional services and information for Current Directions in Psychological Science can be found at: Email Alerts: http://cdp.sagepub.com/cgi/alerts Subscriptions: http://cdp.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsReprints.nav Permissions: http://www.sagepub.com/journalsPermissions.nav >> Version of Record - Sep 25, 2013 What is This? Downloaded from cdp.sagepub.com at OhioLink on January 4, 2014 485087 research-article2013 CDPXXX10.1177/0963721413485087Tucker-Drob et al.Genetics of Cognition Genetic and Environmental Influences on Cognition Across Development and Context Current Directions in Psychological Science 22(5) 349­–355 © The Author(s) 2013 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/0963721413485087 cdps.sagepub.com Elliot M. Tucker-Drob, Daniel A. Briley, and K. Paige Harden Department of Psychology and Population Research Center, University of Texas at Austin Abstract Genes account for between approximately 50% and 70% of the variation in cognition at the population level. However, population-level estimates of heritability potentially mask marked subgroup differences. We review the body of empirical evidence indicating that (a) genetic influences on cognition increase from infancy to adulthood, and (b) genetic influences on cognition are maximized in more advantaged socioeconomic contexts (i.e., a Gene × Socioeconomic Status interaction). We discuss potential mechanisms underlying these effects, particularly transactional models of cognitive development. Transactional models predict that people in high-opportunity contexts actively evoke and select positive learning experiences on the basis of their genetic predispositions; these learning experiences, in turn, reciprocally influence cognition. The net result of this transactional process is increasing genetic influence with increasing age and increasing environmental opportunity. Keywords cognitive ability, intelligence, Gene × Environment interaction, behavior genetics, cognitive development Intelligence is mostly a matter of heredity, as we know from studies of identical twins reared apart. . . . Social programs that seek to raise I.Q. are bound to be futile. Cognitive inequalities, being written in the genes, are here to stay, and so are the social inequalities that arise from them. What I have just summarized, with only a hint of caricature, is the hereditarian view of intelligence. —Jim Holt, New York Times Sunday Book Review, March 27, 2009 In modern industrialized populations, cognition is ap­prox­imately 50% to 70% heritable (Bouchard & McGue, 1981). This means that genetic differences between people account for 50% to 70% of the variation in performance on tests of cognitive abilities, such as reasoning, memory, processing speed, mental rotation, and knowledge. These heritability estimates are based on studies of identical and fraternal twins raised together, identical twins separated at birth and raised apart, and adoptive families. All of these designs hinge on the question of whether more genetically related individuals (e.g., biological siblings versus adoptive siblings) are also more similar in their cognitive ability. More recently, molecular genetic studies of unrelated persons have converged on similar heritability estimates (Chabris et al., 2012; Davies et al., 2011). Despite the vociferous objections of critics of behavioral genetic research (e.g. Charney, 2012), whether genetic differences between individuals account for variation in cognition is no longer a question of serious scientific debate. As McGue (1997, p. 417) commented, “That the debate now centres on whether IQ is 50% or 70% heritable is a remarkable indication of how the nature-nurture question has shifted.” These heritability estimates have been interpreted— both by scientists and by the lay public—to mean that environmental experiences have a minimal impact on cognition. In this article, we describe an alternative interpretation of what it means for cognition to be heritable: Rather than rendering environments impotent, genetic influences on cognition are the result of accumulating environmental experiences and depend on exposure to high-quality environmental contexts over time. Corresponding Author: Elliot M. Tucker-Drob, Department of Psychology, University of Texas at Austin, 108 E. Dean Keeton Stop A8000, Austin, TX 78712-1043 E-mail: tuckerdrob@utexas.edu Downloaded from cdp.sagepub.com at OhioLink on January 4, 2014 Tucker-Drob et al. 350 An “Educational” Example: The Heritability of Educational Attainment in the 20th Century To illustrate how genetic influences on psychosocial outcomes can depend on the environment, we begin with an example involving generational differences in educational attainment. After World War II, there was a dramatic expansion of access to education in Norway. In 1960, the average educational attainment for Norwegian adults was 5.92 years; by 2000, it was 11.86 years (Barro & Lee, 2000). This expansion was driven by postwar increases in government-sponsored student loans and by a social climate that increasingly valued education (Kuhnle, 1986). In contrast, prewar educational opportunities in Norway were less universal, and educational attainment was much more dependent on family social class. Over this same period, the heritability of educational attainment nearly doubled, from 40% for Norwegian male twins born before 1940 to approximately 70% for those born after 1940 (Heath et al., 1985). If it were indeed the case, as suggested by the New York Times quote above, that heritability imposes an upper limit on the effectiveness of social change, then why would sweeping social changes be accompanied by an increase in both the level and the heritability of educational attainment? One explanation is that, as social opportunity increases, a person’s educational attainment becomes increasingly a function of his or her individual characteristics—interests, motivation, work ethic, and scholastic aptitude—rather than social position. To the extent that these individual characteristics reflect genetic differences between people, however slight, then the net result of individuals’ selecting their own educational paths is greater heritability of educational attainment. This explanation implies that heritability is maximized when people are free to select their own experiences. This same process may be a key mechanism for cognitive development. Transactional Models of Cognitive Development Gene-environment correlation—in which environmental experiences become sorted on the basis of individuals’ genetically influenced traits—is not specific to educational attainment. Rather, behavioral genetic studies have found that a broad array of presumably “environmental” experiences—such as negative life events, relationships with parents, and experiences with peers—are themselves heritable (Kendler & Baker, 2007). That is, genetically similar people (such as monozygotic twins) experience more similar environments, whereas genetically dissimilar people (such as adoptive siblings) experience less similar environments. Transactional models posit that these gene-environment correlations are key mechanisms of cognitive development. Early genetically influenced behaviors lead a person to select (and to be selected into) particular types of environments; these environments, in turn, have causal effects on cognition and serve to reinforce the original behaviors that led to those experiences. As Dickens and Flynn (2001, p. 347) stated, “higher IQ leads one into better environments causing still higher IQ, and so on.” In addition to early cognitive ability, “noncognitive” traits, such as motivation and intellectual interest, may also lead children into cognition-enhancing environments (TuckerDrob & Harden, 2012b). For instance, higher achievement motivation may lead students to enroll in more challenging courses, spend free time engrossed in intellectually stimulating activities, and engage parents, peers, and teachers in more sophisticated discourse. Longitudinal research has documented bidirectional associations consistent with transactional processes. For example, not only does greater parental stimulation predict children’s subsequent test scores, but children’s test scores also predict higher subsequent stimulation by parents (e.g., Lugo-Gil & Tamis-LeMonda, 2008; TuckerDrob & Harden, 2012a). Moreover, children’s dispositions toward engaging with stimulating learning environments predict later test scores, and children’s test scores predict their later dispositions toward learning (Marsh, Trautwein, Lüdtke, Köller, & Baumert, 2005). Such positive feedback loops may yield increasing dividends. If genes influence a child’s early behaviors, even small initial genetic differences can be compounded via gene-environment correlation, leading to large estimates of genetic effects. In this way, the genetic effects on individual differences in psychological development can depend on reciprocal transactions with the environment. As Scarr and McCartney (1983) explained, We do not think that development is precoded in the genes and merely emerges with maturation. Rather, we stress the role of the genotype in determining which environments are actually experienced and what effects they have on the developing person. (p. 425) Transactional models propose that genetic differences between people matter for cognition because initial genetic differences lead to different environmental experiences. The “end state” of this transactional process— high levels of and high heritability of cognitive ability—is therefore expected to differ depending on the quality and availability of environmental experiences. Thus, differences in heritability between groups can provide important information about the developmental processes undergirding cognition. Contemporary research in behavioral genetics of cognition has identified two Downloaded from cdp.sagepub.com at OhioLink on January 4, 2014 Genetics of Cognition 351 dimensions along which heritability differs: age/ development and socioeconomic advantage. Below, we summarize results from these two streams of research and describe how these results can be understood within the framework of transactional models. Developmental Changes in Heritability Children are born with all of their genes, and they experience an ever-wider array of environmental inputs as they develop. One might therefore expect that genetic variation will account for less and less variation in psychological outcomes with age. However, in contrast to this intuitive hypothesis, genetic influences on cognition actually increase substantially with age. Aggregated results from 11 unique longitudinal twin and adoption studies of cognition are shown in Figure 1. In infancy, genes account for less than 25% of the variation in cognition, whereas the shared family environment accounts for approximately 60%. By adolescence, however, genes account for approximately 70% of the variation in cognition, and the shared environment accounts for virtually no variation. These age-related patterns were identified in cross-sectional analyses originally by McCartney, Harris, and Bernieri (1990) and McGue, Bouchard, Iacono, and Lykken (1993), and more recently by Haworth et al. (2009). We can understand the developmental increase in the heritability of cognition within the transactional framework. As children select and evoke experiences in line with their genetic predispositions, and as these experiences, in turn, stimulate their cognitive development, early genetic influences on cognition will become amplified. This compounding process is expected to become accelerated as children gain increasingly more autonomy in selecting their peer groups, afterschool activities, academic courses, and other positive learning experiences. A second explanation for the developmental increase in heritability is that “new” genes that did not previously influence cognition may become activated later in development. For example, the biological changes of puberty may trigger changes in gene expression, or genetic differences that were not previously relevant for cognition may become relevant as children’s social contexts change. In fact, both “new” gene activation and gene-environment transactions may contribute to developmental increases in the heritability of cognition, and the relative importance of each process may differ across the lifespan. Longitudinal behavioral genetic studies have indicated that activation of “new” genes may be the primary mechanism underlying increasing heritability in early childhood, whereas transactional processes may be the primary mechanism underlying increasing heritability in middle childhood and adolescence (Briley & Tucker-Drob, in press). Unfortunately, much of what is known about the behavioral genetics of cognitive development has been Fig. 1. Proportion of variance in cognition as a function of age. Shading around each line represents the imprecision of the estimate (± 1 SE). The family environment, often termed the shared environment, represents environmental influences that make siblings raised in the same family more similar to one another. The unique environment, often termed the nonshared environment, represents environmental influences that differentiate siblings raised in the same family. Data were aggregated from published reports, based on 11 unique longitudinal twin and adoption samples (weighted by the precision of the individual estimates): the Colorado Adoption Project (Petrill et al., 2004), the Early Childhood Longitudinal Study—Birth Cohort (Tucker-Drob, Rhemtulla, Harden, Turkheimer, & Fask, 2011), the Longitudinal Twin Study (Bishop et al., 2003), the Louisville Twin Project (McArdle, 1986), the MacArthur Longitudinal Twin Study (Cherny et al., 2001), a Moscow community sample (Malykh, Zyrianova, & Kuravsky, 2003), the Netherlands Twin Registry (Hoekstra, Bartels, & Boomsma, 2007; Polderman et al., 2006; van Soelen et al., 2011), the Twins Early Development Study (Davis, Haworth, & Plomin, 2009), and the Western Reserve Reading Project (Hart, Petrill, Deater-Deckard, & Thompson, 2007). Articles were identified by searching abstracts in PsycINFO. From the search results, we included longitudinal studies with samples of siblings with varying degrees of genetic relatedness, complete cross-time and within-time sibling correlations (or parameters from behavioral genetic models producing expectations for these correlations), measurement using an objective cognition/intelligence test, and participants under age 19 at both baseline and at least one follow-up measurement occasion. derived from convenience samples of twins in the United States and from representative samples of twins from less racially and socioeconomically diverse populations. Thus, the trend of increasing heritability with age may not apply as well to groups with low socioeconomic status (SES). Next we discuss emerging research on the question of whether the heritability of cognition differs as a function of SES. Socioeconomic Differences in Heritability Under a transactional model of cognitive development, children are expected to select and evoke their environmental experiences on the basis of genetically influenced dispositions, but this process depends on the existence Downloaded from cdp.sagepub.com at OhioLink on January 4, 2014 Tucker-Drob et al. 352 of adequate opportunities for such experiences. SES, which is typically measured using parental income, educational attainment, occupational status, or some combination of the three, is an omnibus marker of the quality of environmental opportunity. In high-SES contexts, children have abundant opportunities to select and evoke positive learning experiences on the basis of their genetically influenced motivations and proclivities. In low-SES contexts, children are less likely to receive adequate opportunities for cognitively stimulating experiences, both at home and in school. For example, children from disadvantaged backgrounds typically have less access to enriching books and other learning materials, less rigorous academic experiences, and lower quality interactions with both peers and adults (Duncan & Murnane, 2011). Because low-SES contexts do not support transactional processes, it is predicted that genetic potentials for cognitive development are not fully realized (Bronfenbrenner & Ceci, 1994). Indeed, research on Gene × SES interaction has indicated that genetic influences on cognition are suppressed by socioeconomic disadvantage. For children in low-SES contexts, the heritability of cognition approaches zero, whereas for children in advantaged contexts, genes account for as much as 80% of individual differences in cognition (see Fig. 2). This Gene × SES interaction has been found in young children (Scarr-Salapatek, 1971; Turkheimer, Haley, Waldron, D’Onofrio, & Gottesman, 2003), adolescents (Harden, Turkheimer, & Loehlin, 2007; Rowe, Jacobson, & van den Oord, 1999), and adults (Bates, Lewis, & Weiss, in press). Moreover, although socioeconomic disparities in cognition and achievement are often interpreted as being the result of inequalities in education, Tucker-Drob, Rhemtulla, Harden, Turkheimer, and Fask (2011) found evidence for a Gene × SES interaction on infants’ cognitive development between 10 months and 2 years of age, more than 3 years before the typical age of kindergarten entry. Specifically, for children in high-SES homes, genetic influences on cognition increased from approximately 0% at 10 months to 50% at 2 years, whereas for children in low-SES homes, genetic influences on infant cognition remained very close to 0% across the study period. That is, disadvantaged children did not show the expected developmental increase in the heritability of cognition. In follow-up work with this sample, a similar Gene × SES interaction was found on school-readiness skills (specifically mathematics) at age 4 years (Rhemtulla & Tucker-Drob, 2012). However, the interaction at 4 years was found to be entirely independent of the Gene × SES interaction earlier in development. This result suggests that Gene × SES interactions on cognition occur throughout infancy and early childhood, not because early life disadvantages have left indelible effects on cognition, but rather because low SES Fig. 2. Variance in mental ability as a function of SES in late infancy (age 2 years) (A). Data come from a nationally representative sample of American twins, 25% of whom lived below the poverty line (Tucker-Drob, Rhemtulla, Harden, Turkheimer, & Fask, 2011). Variance in cognitive aptitude as a function of parental income in adolescence (age 17 years) (B). Data come from a positively selected sample of adolescent twins who sat for the National Merit Scholarship Qualifying Test (Harden, Turkheimer, & Loehlin, 2007), very few of whom were likely to be living in poverty. Because a Gene × SES interaction was detected in this more positively selected sample, Harden et al. (2007) concluded that “genotype-by-environment interactions in cognitive development are not limited to severely disadvantaged environments, as has been previously suggested.” Shading around each line represents the imprecision of the estimate (± 1 SE). The family environment, often termed the shared environment, represents environmental influences that make siblings raised in the same family more similar to one another. The unique environment, often termed the nonshared environment, represents environmental influences that differentiate siblings raised in the same family. Downloaded from cdp.sagepub.com at OhioLink on January 4, 2014 Genetics of Cognition 353 children are recurrently exposed to poor environments that have novel, yet analogous, interactions with their genes at different ages. Although a number of studies have replicated Gene × SES interactions on cognition, a handful of notable studies with sound designs have failed to replicate these effects (see Hanscombe et al., 2012 for a review). It is noteworthy that these failures to replicate have predominantly been in northern European nations, where social welfare systems are more comprehensive, whereas most of the positive results have been obtained in the United States, where social class differences in educational opportunity are vast. Socioeconomic disadvantage may not disrupt gene-environment transactions to the same extent in countries that ensure access to adequate medical care and high-quality education. Future research should identify the specific circumstances in which these Gene × SES interactions hold, by taking into account both macroenvironmental contexts (e.g., regional and national characteristics) and school- and family-level differences in economic opportunity and constraint. Conclusions and Outlook The results reviewed here suggest a provocative reconceptualization of the relationship between social opportunity and the magnitude of heritable variation in cognition. We began this article with a quote that illustrates the common view that heritability estimates provide an “upper bound” on the effects of social intervention—if cognition is very heritable, then the environment cannot matter as much. In fact, research on how the heritability of cognition differs across development and across context suggests that genetic influences on cognition are maximized by environmental opportunity. The highest heritability estimates are obtained for older children and adolescents from economically advantaged homes—that is, among children who have the autonomy to select environmental experiences consistent with their own interests and who have an array of high-quality experiences to choose from. As social, educational, and economic opportunities increase in a society, genetic differences will account for increasing variation in cognition—and perhaps ultimately in educational and economic attainment. Distinguishing transactional processes from the “direct” influences of genes is more than a simple academic exercise. As Plomin, DeFries, and Loehlin (1977) wrote: Although formally it may not matter one whit in which way the effects of the genes are mediated, in practice it often matters quite a few whits, especially if one should happen to be interested in intervening in the process. (p. 321) Indeed, child-driven transactions may be critical for intervention success. For example, Epps and Huston (2007) found that a poverty intervention changed parenting behaviors indirectly through effects on child behaviors; there was no immediate, direct effect of the intervention on parenting behaviors. In other words, the intervention was unable to directly influence parents to provide higher quality care but was able to change child behaviors to evoke more effective care from their parents. By determining the specific environmental transactions that amplify genetic influences across development and across contexts, researchers may uncover new opportunities for environmental intervention. Recommended Reading Bronfenbrenner, U., & Ceci, S. J. (1994). (See References). A theoretical account of how social context and genetic potentials interact to influence positive developmental outcomes. Dickens, W. T., & Flynn, J. R. (2001). (See References). An indepth treatment of how transactional processes can cause small genetic differences to be amplified to result in large estimates of heritability. Nisbett, R. E., Aronson, J., Blair, C., Dickens, W., Flynn, J., Halpern, D. F., & Turkheimer, E. (2012). Intelligence: New findings and theoretical developments. American Psychologist, 67, 130–159. A survey of the past 15 years of research on intelligence, including a section containing a review of empirical studies on “Social Class and Heritability of Cognitive Ability.” Scarr, S., & McCartney, K. (1983). (See References). A groundbreaking article on how genetic differences can come to be correlated with environmental differences over development. Tucker-Drob, E. M., & Harden, K. P. (2012b). See reference list. A recent study detailing a possible mechanism through which Gene × SES interactions might operate. Declaration of Conflicting Interests The authors declared that they had no conflicts of interest with respect to their authorship or the publication of this article. Funding This research was supported by the National Institute of Child Health and Human Development (NICHD) Grant R21-HD069772. D. Briley was supported by NICHD Grant T32-HD007081. The Population Research Center at the University of Texas at Austin is supported by NICHD Grant R24-HD042849. References Barro, R. J., & Lee, J. W. (2000). International data on educational attainment: Updates and implications (CID Working Paper No. 42). Cambridge, MA: Center for International Development. Downloaded from cdp.sagepub.com at OhioLink on January 4, 2014 Tucker-Drob et al. 354 Bates, T. C., Lewis, G. J., & Weiss, A. (in press). Childhood socioeconomic status amplifies genetic effects on adult intelligence. Psychological Science. Bishop, E. G., Cherny, S. S., Corley, R., Plomin, R., DeFries, J. C., & Hewitt, J. K. (2003). Development genetic analysis of general cognitive ability from 1 to 12 years in a sample of adoptees, biological siblings, and twins. Intelligence, 31, 31–49. Bouchard, T. J., & McGue, M. (1981). Familial studies of intelligence: A review. Science, 212, 1055–1059. Briley, D. A., & Tucker-Drob, E. M. (in press). Explaining the increasing heritability of cognitive ability across development: A meta-analysis of longitudinal twin and adoption studies. Psychological Science. Bronfenbrenner, U., & Ceci, S. J. (1994). Nature-nurture reconceptualized in developmental perspective: A bioecological model. Psychological Review, 101, 568–586. Chabris, C. F., Hebert, B. M., Benjamin, D. J., Beauchamp, J. P., Cesarini, D., van der Loos, M. J. H. M., . . . Laibson, D. (2012). Most reported genetic associations with general intelligence are probably false positives. Psychological Science, 23, 131–1323. Charney, E. (2012). Behavior genetics and post genomics. Behavioral and Brain Sciences 35, 331–358. Cherny, S., Fulker, D. W., Emde, R. N., Plomin, R., Corley, R. P., & DeFries, J. C. (2001). Continuity and change in general cognitive ability from 14 to 36 months. In R. N. Emde & J. K. Hewitt (Eds.), Infancy to early childhood: Genetic and environmental influences on developmental change (p. 206–220). New York, NY: Oxford University Press. Davies, G., Tenesa, A., Payton, A., Yang, J., Harris, S. E., Liewald, D., . . . Deary, I. J. (2011). Genome-wide association studies establish that human intelligence is highly heritable and polygenic. Molecular Psychiatry, 16, 996–1005. Davis, O. S. P., Haworth, C. M. A., & Plomin, R. (2009). Dramatic increase in heritability of cognitive development from early to middle childhood: An 8-year longitudinal study of 8,700 pairs of twins. Psychological Science, 20, 1301–1308. Dickens, W. T., & Flynn, J. R. (2001). Heritability estimates versus large environmental effects: The IQ paradox resolved. Psychological Review, 108, 346–369. Duncan, G. J., & Murnane, R. J. (Eds.). (2011). Whither opportunity? Rising inequality, schools, and children’s life chances. New York, NY: Russell Sage. Epps, S. R., & Huston, A. C. (2007). Effects of a poverty intervention policy demonstration on parenting and child behavior: A test of the direction of effects. Social Science Quarterly, 88, 344–365. Hanscombe, K. B., Trzaskowski, M., Haworth, C. M. A., Davis, O. S. P., Dale, P. S., & Plomin, R. (2012). Socioeconomic status (SES) and children’s intelligence (IQ): In a UK-representative sample SES moderates the environmental, not genetic, effect on IQ. PLoS ONE, 7, e30320. doi:10.1371/journal.po...
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Human Behavior and Cognition Development
Parental modeling and disciplining of a child are important is the shaping of a child’s
behavior. There seems to be the influence of family socialization in moral shapeup. Early childparent interaction informs conscience and the extent to which they embrace parent’s behaviors.
Children who grow with families that are responsive, adopt the characters of their parents and
this positively shapes their behaviors and consciences. This shows that early child-parent
interactions are key in shaping the moral developments for the child. However, there also seems
to be internal guidance in a child that guides in moral values during growth (Kochanska,...


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