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Evolutionary Developmental Psychology

Evolutionary Developmental Psychology

Child Development, January/February 2000, Volume 71, Number 1, Pages 57Ð65

Evolutionary Developmental

David C. Geary and David F. Bjorklund

Evolutionary is the study of the genetic and ecological mechanisms that govern the development of social and cognitive competencies common to all beings and the epigenetic (geneÐ environment interactions) processes that adapt these competencies to local conditions. The basic assumptions and domains of this emerging Þeld, as related to human life history and social and cognitive development, are outlined, as are implications for issues of importance in contemporary society.

INTRODUCTION tal psychology, that is, to outline basic assumptions, deÞne domains of study, and discuss future directions. Evolutionary developmental is the study of Among the fundamental issues that must be ad- how genetic systems are expressed during develop- dressed by this emerging Þeld are the function of de- ment, how the of the developing velopment and evolutionary change in the develop- inßuences the expression of one genetic system or an- mental period, issues discussed in the Þrst section other, and how modiÞcations in timing of develop- below. The second and third sections focus on the mental processes inßuence (Gilbert, Opitz, & Raff, 1996; Waddington, 1942). Of particular impor- two core areas of developmental psychology, social tance is , Òthe sum of the genetic and non- and cognitive development, respectively, and provide genetic factors acting on cells to selectively control the an evolutionary framework for conceptualizing empir- expression that produces increasing phenotypic ical and theoretical work in these areas. The last section complexity during development. The is the addresses the relationship between evolved pheno- starting point and the phenotype is the endpoint of types and their expression in contemporary society. epigenetic controlÓ (Hall, 1992, p. 215). provide the instructions for guiding the development of the core phenotypes, such as body structure and social EVOLUTION AND DEVELOPMENT behaviors, of the . Sensitivity to internal (e.g., Function of development. A long developmental hormones) and external (e.g., population density) con- period has a clear risk, death before the age of repro- ditions ensures that the expression of the genotype is duction, and thus would only evolve if there were responsive to social and ecological factors such that the individualÕs physical, behavioral, and psychological beneÞts that outweighed this risk. Comparative phenotypes are adapted, during the course of develop- studies suggest that one function and an important ment, to these conditions (e.g., population density). adaptive beneÞt of delayed maturation is the accom- The development of most human phenotypes and panying ability to reÞne the physical, social, and associated individual variability among these pheno- cognitive competencies that support survival and re- types will be inßuenced by a mixture of genetic and production in adulthood (Mayr, 1974). For instance, ecological mechanisms, that is, by epigenetic pro- an extended juvenile period is found in all social cesses (Hall, 1992; Scarr, 1992). These processes ensure and the length of this period increases commonality in the basic phenotypes of all with increases in the complexity of the speciesÕ so- and reßect the evolutionary history of our species but cial system (Joffe, 1997). These patterns support the at the same time allow for the ontogenetic view that one function of delayed maturation is to of these phenotypes to the local ecology. The goals of allow juveniles to practice and reÞne the sociocogni- evolutionary developmental psychology, the sister tive competencies associated with survival and re- discipline of evolutionary , are production (e.g., competing for mates) in adulthood. to identify the social, psychological, cognitive, and An extended developmental period is also related to neural phenotypes that are common to human beings, enhanced tool use in some species and greater and to other species, and to identify the genetic and knowledge of the local ecology, both of which facili- ecological mechanisms that shape the development of tate later foraging (Byrne, 1995; Geary, 1998). these phenotypes and ensure their adaptation to local conditions. The goal here is to provide the skeletal © 2000 by the Society for Research in Development, Inc. framework for the Þeld of evolutionary developmen- All rights reserved. 0009-3920/2000/7101-0007

58 Child Development

For humans, play, social interactions, and explora- Table 1 Stages of Human Life History tion of the environment and objects appear to be the Infancy mechanisms through which these emerging compe- Defining feature: For mammals, this is the time of breast-feeding. tencies are practiced and reÞned during development Human characteristics: In hunter-gatherer societies, are (e.g., Pellegrini & Smith, 1998). In theory, these child- typically breastfed until the age of 3 years. The age of initiated activities provide experiences with the so- weaning in humans is shorter than that found in a close cial, biological (e.g., prey species), and physical world relative, the chimpanzee, where infants are weaned between that interact with underlying genetic systems to pro- 4 and 5 years of age. duce the physical, social, cognitive, and neural phe- Childhood notypes associated with the survival and reproduc- Defining feature: The period between weaning and the ability to eat tion of our ancestors (Geary, 1998; Scarr & McCarthy, foods. 1983). Child-initiated social play and exploration are Human characteristics: This period is longer in humans than in intimately linked to cognitive and neural develop- other primates and appears to be associated with a relatively ment in that these activities result in the environmental short infancy. In hunter-gatherer societies, childhood experiences that are an integral part of the epigenetic encompasses the ages of 3 to 7 years, 7 years being the age at which the first adult molars appear and dependence on processes that result in adult phenotypes (Greenough, decreases. During this time, the responsibility for feeding 1991; Hall, 1992). One resulting prediction is that the re- children often shifts from the mother to the wider lationship between early play and social activities and (e.g., older siblings), although social and psychological later competencies will be activity speciÞc. For instance, dependence on parents continues. exploration of the wider ecology is associated with an Juvenility improved ability to mentally represent and navigate in Defining feature: Period between weaning or childhood and sexual the physical world (Matthews, 1992), but is not neces- maturation and social independence. This period is common to sarily associated with improved abilities in all spatial social mammals and is characterized by social and other forms domains (e.g., remembering the location of objects). of play. Evolutionary change. In considering evolutionary Human characteristics: In hunter-gatherer societies this period change in the developmental period, it is useful to ranges between 7 years and the mid teens. As with other social mammals, this is often a time of social and other forms of play, conceptualize human life history as being comprised as well as a time during which parental dependency decreases of developmental stages (Charnov, 1993). These stages and peer influences increase. are useful for considering general social and develop- ment goals and changes in these goals at different points in the life span and do not, for instance, appear Defining feature: Encompasses the process of physical, social, and personal maturation. In many primates, the transition between to map onto any developmental stages for the cogni- juvenility and adulthood is not marked by an obvious period of tive modules described later. Bogin (1997) provided adolescence (e.g., no growth spurt). one such framework and argued that human develop- Human characteristics: Clear growth spurt, and prolonged period of ment can be understood in terms of Þve stages: infancy, physical maturation. This is generally a time to explore adult childhood, juvenility, adolescence, and adulthood. The social and sexual roles and refine reproduction-related social basic features of these stages, as found in humans in strategies (e.g., those associated with competing for mates). During this time, the social activities common to juvenility hunter-gatherer societies and in other mammals, are become increasingly adult-like (e.g., play fighting gradually described in Table 1 (Bogin, 1997; Lancaster & Lan- escalates to real fighting). Early physical maturation and caster, 1983; Leigh, 1996). The stages are characterized prolonged dependence on parents (e.g., to complete schooling) by differing degrees of physical development, social has increased the length of this period in industrial, compared dependence, and social goals. to hunter-gatherer, societies. Based on evidence derived from the fossil record Adulthood (e.g., adult size), it has been estimated that the age of Defining features: Period of mature reproductive activities, which maturation for Australopithecus afarensis, A. africanus, involve finding a mate or mates (e.g., competing for mates or and Homo habilis was similar to that found in the mod- choosing mates) and investment in offspring. For 95% to 97% ern chimpanzee (Pan troglodytes), that is, nine to eleven of mammalian species, there are large differences in these activities, with males focusing most of their reproductive years (Bogin, 1997; McHenry, 1994). In other words, energies on mating and females on parenting. two to four million years ago, our ancestors were sex- Human characteristics: As with other mammals, the finding of a ually mature at around 10 years and probably began mate and investing in any resulting offspring are the focus of to reproduce a few years later. The estimated age of this period in hunter-gatherer, and other, societies. Humans are maturation of our most recent ancestor, H. erectus, was atypical among mammals, in that men invest in the well-being between 12 and 13 years, whereas that of modern hu- of children, though less so than women do, and women, like men, compete for mates. mans is in the late teens to early twenties (Tanner, 1990).

Geary and Bjorklund 59

Thus, the length of the developmental period has ßects changes in the nature of social relationships. nearly doubled since the of A. afarensis. All Social relationships in infancy and childhood are of the stages described in Table 1 are longer in humans largely survival related, whereas those during juve- than in other primates and almost certainly longer than nility appear to involve a preparation for adult repro- in our hominid ancestors (Bogin, 1997; Leigh, 1996). duction. The nature of social relationships changes The substantial increase in the length of the develop- again during adolescence and adulthood, when they mental period suggests that our ancestors were more are focused more directly on reproductive issues. successful at keeping their offspring alive than were Infancy and childhood. There is little question that other primates; child mortality rates in hunter-gatherer the primary relationship in infancy and childhood is societies are about 50% compared with 67% to nearly between the child and his or her parents (Bowlby, 90% in other primates (Lancaster & Lancaster, 1983). 1969). The associated attachment-related behaviors, Moreover, the lengthening of the developmental period, such as stranger anxiety and separation anxiety, along with a threefold increase in brain volume since emerge at about the same age in all human societies A. afarensis, suggests a substantial increase in the com- and at about the same age in the chimpanzee, suggest- plexity of hominid social systems and in the ability to ing a long evolutionary history (Bard, 1995). Some exploit biological and physical resources (e.g., through form of attachment is, in fact, common to primates tool use). An extended developmental period, along and appears to function to reduce mortality with the increased social play and exploratory behavior, risks by keeping the infant in close proximity to its would enable the reÞnement of increasingly sophisti- parent or parents and by increasing the level of paren- cated physical, social, and cognitive competencies. tal investment (Bard, 1995; Bowlby, 1969; MacDonald, Adaptive value of immaturity. Not all features of the 1992); the latter refers to resources, such as time and developmental period are a preparation for adult sur- food, provided to offspring at a cost to the parent vival and reproduction. A basic assumption of evolu- (e.g., delayed birth of the next offspring, see Geary, tionary developmental psychology is that natural se- 2000; Trivers, 1974). There are, however, individual lection has resulted in cognitive and social traits that differences in the nature or quality of the attachment support survival of individuals at all stages of devel- relationship across dyads of parents and children opment, and that infants, children, juveniles, and ado- (Ainsworth & Bell, 1970), suggesting that attachment lescents may have evolved speciÞc adaptive behaviors emerges through an epigenetic process. In other to deal with their developmentally deÞned niches words, the attachment process is biologically driven, (Bjorklund, 1997). When such a perspective is applied but the nuances of this relationshipÑthe measurable to human cognitive and social development, one sees phenotypeÑare shaped by the nature of the parentÐ cognitive or social immaturity in a different light. child relationship. Seemingly ÒimmatureÓ behavior may have been se- One implication, and an important conceptual lected as a way young can negotiate the framework for future studies, is that different forms preadult years (Pellegrini & Smith, 1998). As an exam- of attachment reßect an adaptation to different social ple, Turkewitz and Kenny (1982) argued that the im- contexts (MacDonald, 1992). In theory, these adapta- mature sensory abilities of infants (e.g., poor eye tions would reßect behavioral and psychological ad- sight) may serve as a form of protection from over- justments to maintain or increase levels of parental in- stimulation (see Bjorklund, 1997, for a review). Aspects vestment (Trivers, 1974), although empirical research of cognitive immaturity, such as an egocentric per- on attachment generally has not approached these in- spective and poor metacognition (see Bjorklund, dividual differences from this perspective. A related 1997), may have an adaptive role for children as well. issue is whether early attachment patterns inßuence For instance, their short auditory memory span may later reproductive strategies (Belsky, Steinberg, & serve to reduce the amount of language processed and Draper, 1991). There is indeed a correlation between thus aid in comprehension. receiving low or inconsistent levels of parental invest- ment in childhood, an insecure attachment to parents, and later instability in marital relationships and thus SOCIAL DEVELOPMENT lower levels of investment in any resulting children. Sociocognitive competencies, such as the ability to pro- However, it is not clear if this correlation is caused by duce and respond to communicative behaviors (e.g., early attachment patterns or reßects heritable traits, vocalizations), are a requisite feature of survival and that is, genes that inßuence both marital instability reproduction in all primates (Hauser, 1996). Develop- and low levels of parental investment (MacDonald, ment not only enables the reÞnement of these socio- 1997). Future studies of potential social and genetic cognitive competencies through social play, it also re- inßuences on attachment and later parenting might

60 Child Development follow the approach recently used by Rowe and his Adolescence and adulthood. Adolescence is deÞned colleagues to study genetic and social inßuences on by the physical changes that prepare individuals for individual differences in social (Rowe, adult reproductive activities, such as giving birth or Almeida, & Jacobson, 1999). physical competition for social status, an increasing Juvenility. During juvenility, the focus of human so- interest in members of the opposite sex, and an esca- cial relationships shifts from parents to peers, as is lation of the forms of social competition described found in other social mammals (Bogin, 1997; Harris, above (Tanner, 1990). As an example, in mammals, 1995). Across primate species, a long juvenile period is including humans, the play Þghting of males be- associated with a larger neocortex and a complex social comes increasingly intense and adult-like during system (Barton, 1996; Joffe, 1997), suggesting, as noted adolescence. For humans, early courtship and pre- earlier, that one goal of juvenility is to practice and re- sexual (sometimes sexual) heterosexual relation- Þne sociocognitive competencies. An intriguing feature ships emerge, and appear to provide the experi- of human social behavior during juvenility is the ten- ences needed to establish and maintain the more dency of children to segregate themselves into same- stable relationships of adulthood (Bogin, 1997; Mac- sex groups and to engage in different forms of social coby, 1998). play within these groups, although these differences Early adulthood is the reproductive period and in begin to emerge in childhood (Maccoby, 1988, 1998). hunter-gatherer societies usually begins in the late From an evolutionary perspective, these sex differ- teens for and a few years later for boys (Bogin, ences are predicted to be a reßection of and a prepara- 1997). Although there are similarities in the reproduc- tion for sex differences in adult reproductive activities, tive activities of men and women, there are differ- at least in hunter-gatherer societies and presumably ences as well. For instance, men engage in more phys- during the course of human evolution (see Bjorklund & ical, coalition-based intrasexual aggression for the Shackelford, 1999; Geary, 1998, 1999, 2000). establishment of social than do women, As with juvenile males in most other mammals, and women spend more time in parenting activities boysÕ play is largely focused on the achievement of than do men (Bjorklund & Shackelford, 1999; Geary, social status and social dominance and includes rough- 1998). In hunter-gatherer and other preindustrial so- and-tumble play (e.g., play wrestling) and group- cieties, women continue having children until meno- level competition (e.g., team sports, Pellegrini & Smith, pause and spend their post-menopausal years raising 1998; Smith, 1982). These activities are a preparation their youngest children and investing in their grand- for the physical and often deadly forms of male-on- children. Older men, in contrast, often attempt to con- male aggression in adulthood that is common in pre- tinue their reproductive activities by marrying younger industrial societies and related to striving for social wives (Bogin, 1997; Lancaster & Lancaster, 1983). These dominance and mate acquisition (Geary, 1998; Keeley, patterns suggest different life histories for women 1996). The social activities of girls are more communal and men during human evolution and, as a result, de- than those of boys and are focused on the develop- velopmental sex differences in social goals, behav- ment and maintenance of a small number of intimate iors, and motivations are expected, and found (Geary, and reciprocal relationships with other girls. In adult- 1998, 1999). hood, these networks appear to provide a system of Finally, does not eliminate the social support and stability. The achievement of a sta- many deleterious changes associated with adult ag- ble social network in turn is associated with reduced ing but rather, under some conditions, can operate to morbidity risks for children and thus appears to be an delay the onset of these changes (Charnov, 1993). evolved parenting strategy (Flinn & England, 1995; During hominid evolution there has been a clear in- Geary, 1998). This does not mean that girls do not com- crease in the length of the lifespan, suggesting that a pete with one anotherÑthey do: they back bite, shun, slowed rate of maturation and the associated extension and gossip, the goal of which appears to be to disrupt of adulthood has resulted in reproductive advan- the social networks of their competitors (termed Òre- tages. The advantages associated with a longer devel- lational aggression,Ó Crick & Bigbee, 1998). Although opmental period, as described earlier, could only be it is not certain, girlsÕ relational aggression during juve- supported by a corresponding increase in the lifespan nility might provide practice for later competition over of parents, given the dependency of human children. mates and other resources, just as boysÕ rough-and- The increase in the length of adulthood is thus likely tumble play provides practice for later maleÐmale to be related in part to increases in the level of paren- competition. In any case, the evolutionary perspective tal investment, which in turn would result in repro- will provide a broader context for conceptualizing ductive beneÞts, speciÞcally reductions in child mor- and studying aggression among girls and women. tality rates and potential improvementsÑthrough an

Geary and Bjorklund 61 extended childhood and thus greater opportunity to ual- and group-level systems (see also Caporael, reÞne social and cognitive competenciesÑin the later 1997). Individual-level systems are designed for the social and thereby reproductive competitiveness of on-line monitoring of dyadic interactions and for es- children (Geary, 2000; Lancaster & Lancaster, 1983). tablishing and maintaining interpersonal relation- Nonetheless, the power of natural selection wanes ships. The associated submodules include those that with age, and Òthe beneÞts resulting from evolution- support the reading of nonverbal behavior and facial ary selection evince a negative age correlationÓ (Baltes, expressions, language, and theory of mind (Baron- 1997, p. 367). This is because traits that are expressed Cohen, 1995; Pinker, 1994). The group-level modules only after an individual has reproduced and - parse the social universe into kin, friends (in-group), fully reared offspring are not subject to the same de- and competitors (out-group). gree of selection pressure as traits that directly inßu- Sensitivity to nonverbal behaviors, facial expres- ence survival to reproductive age and successful sions, and other communicative behaviors (e.g., vo- reproduction. As a result, there are no strong selection calizations) of conspeciÞcs, as well as the preferential pressures against deleterious genes that have their in- treatment of kin and the formation of favored and dis- ßuence in (such as those that contribute to favored social groups, are found in many other spe- AlzheimerÕs dementia). In fact, many of these genes cies (Goodall, 1986; Hauser, 1996). A rudimentary the- or other factors (e.g., hormones) that provide adap- ory of mind might be evident in chimpanzees, although tive beneÞts early in life may have more deleterious this is currently debated (e.g., Povinelli & Eddy, 1996; effects later in life. Premack & Woodruff, 1978). Either way, it is clear that humans have the unique ability to form in-groups and out-groups on the basis of social ideologies (e.g., COGNITIVE DEVELOPMENT nationality). The Þrst of two central issues for evolutionary devel- In addition to managing social relationships, our opmental psychology is to identify the evolved do- ancestors had to secure food and other resources from mains of mind, that is, the constellations of cognitive the natural environment, which in turn almost cer- competencies that appear to have been shaped dur- tainly resulted in the evolution of modules for pro- ing evolution (Cosmides & Tooby, 1994; Pinker, 1997). cessing biological and physical information. Biologi- The second issue concerns the mechanisms that gov- cal modules are for categorizing and representing the ern the development of the associated competencies behavior or growth patterns of ßora and fauna in and their adaptation to local (Gelman, 1990; the local ecology, especially species used as food, Siegler, 1996). medicines, or in social rituals (e.g., Berlin, - Domains of mind. Geary (1998) recently proposed love, & Raven, 1973). Physical modules are for guid- that evolved domains of mind be conceptualized as ing movement in three-dimensional physical space, constellations of hierarchically organized modules mentally representing this space, and using physical for processing information in the social, biological, and materials (e.g., stones, metals) for making tools physical worlds, as shown in Figure 1, although there (Pinker, 1997; Shepard, 1994). appear to be other modules that are not represented An important developmental prediction is that the in the Þgure (e.g., for numerical processing). Socio- skeletal competenciesÑthe neural systems that guide cognitive modules are further divided into individ- attention to and processing of the associated infor-

Figure 1 Proposed domains of mind. From Male, female: The evolution of human sex differences (p. 180), by D. C. Geary, 1998, Washington, DC: American Psychological Association. Reprinted with permission.

62 Child Development mationÑof these modules are inherent but are ßeshed Table 2 Predicted Developmental Features of Evolved Cog- out as children engage in social discourse, play, and nitive Modules exploration (Gelman, 1990; see Elman et al., 1996, for Hierarchical Organization an alternative view). The prediction is that natural 1. The modules shown in Figure 1 are very likely to be comprised child-initiated activities are centered on learning of a hierarchy of submodules. For instance, the language system about people and developing social competencies, includes specialized systems for the comprehension and learning about other living things, and learning how production of speech. These, in turn, are supported by sensory the physical world is organized, that is, gaining com- and motor systems for processing and articulating petencies in the areas of folk psychology, folk biology, language sounds. and intuitive physics. The associated activities would 2. The degree to which submodules are specialized is likely to be inversely related to their level in the hierarchy. The most basic include, for instance, sociodramatic play, exploring submodules are likely to be highly specialized, designed to the environment, and object-oriented play. An outline process a restricted range of stimuli, such as specific language of the predicted developmental features of evolved sounds. Modules at the highest level receive information from cognitive modules is presented in Table 2 (Geary, many lower-level modules and may show moderate to high 1998; Gelman, 1990). These predictions may provide a levels of flexibility in the range of stimuli that can be processed and in their output. An example is the apparently infinite useful framework for guiding future cognitive devel- number of utterances that can be generated by the language opmental research and for linking this research to production system. parallel studies in the Þelds of ethnobiology and cog- Sensitive Periods and Child-Initiated Activity nitive anthropology (Atran, 1998). 1. If cognitive modules emerge by means of an epigenetic process, Mechanisms of development. The long developmen- then the development of the associated neural and cognitive tal period of humans argues against the position that systems will be dependent on exposure to domain-specific any inherent features of these cognitive modules and information (e.g., language sounds). Experiences interact with associated behaviors are immutable (Mayr, 1974). the inherent skeletal features of these modules to produce the Rather, there is a core set of cognitive competencies, phenotypic competencies. but the associated phenotypes are modiÞable by ex- 2. A bias in childrenÕs activities and the types of information to which they attend is expected. These activities are expected to periences, that is, these competencies emerge by correspond to the domains shown in Figure 1 (e.g., orienting means of epigenetic processes. For instance, it ap- to people, exploring the environment) and provide the pears that children in all cultures are biologically pre- experiences that are an intimate feature of the epigenetic pared to process and respond to the sounds of all hu- development of the modules. man languages, but the phenotype that eventually 3. Sensitivity to environmental input is expected to be time-lim- emerges is the speciÞc language to which they are ex- ited to some degree; that is, sensitive periods are expected. The posed (Kuhl et al., 1997). Another prediction is that length of the sensitive period may be related to the submodulesÕ level in the hierarchy. Because the functioning of these modules will not be fully elaborated unless chil- higher level submodules may depend on input from lower level dren are exposed to and engage in the relevant activ- modules, the sensitive period for lower-level modules is ities. For instance, Western children have a rudimen- expected to be shorter and occur earlier in life than that for tary understanding of folk biology but, presumably higher level modules. In short, the length of the sensitive period due to a lack of extensive exposure to ßora and fauna, may be directly related to the complexity of the information processed by the module. they do not develop the same degree of folk biological knowledge as is found with individuals in hunter- Implicit Knowledge gatherer and other preindustrial societies (Atran, 1. The skeletal structure of evolved modules reflects the organiza- 1998; Kiel, 1992). tion of the underlying neural systems and the types of informa- tion to which these systems respond. The mechanisms that contribute to this epigenetic 2. Knowledge is built into the organization of these cognitive and process are not well understood but, like natural selec- neural systems, that is, they respond to appropriate ecological tion, appear to involve the generation of variability information and produce intelligent responses to this information. and experiences acting on this variability (Siegler, The functioning of many of these systems is likely to be 1996). The brain and mind appear to generate multiple automatic and largely outside of the realm of conscious control. representations and strategies for processing and act- 3. The degree to which the functioning of modules is relatively ing on social, biological, and physical information. Ex- automatic and the associated knowledge implicit may be inversely related to the modulesÕ level in the hierarchy. perience results in one or a few of these representations Lower-level modules are likely to be characterized by or behavioral strategies being selected over others. The automatic processing (assuming adequate attention to this relative success of one approach or the other for achiev- information) and a high degree of implicit knowledge. Individuals ing the desired goal (e.g., inßuencing other people) ap- are more likely to gain explicit awareness of the output of pears to be the selective process. However, the under- higher-level modules, and the functioning of these modules may be more open to top-down control by the individual. lying cognitive and neural mechanisms that generate

Geary and Bjorklund 63 variability and ensure the selection of successful over sometimes life-threatening risk-taking (e.g., reckless less successful strategies are not well understood (see driving) and deadly forms of male-on-male violence is Shrager & Siegler, 1998, for related discussion) and readily understood in terms of competition for social thus should be one focus of future cognitive develop- status, which in turn often inßuences mating opportu- mental and developmental neuroscientiÞc research. nities (Daly & Wilson, 1988; Geary, 1998). By under- standing the goal of these behaviors and the contexts that are likely to elicit them (e.g., Òsaving faceÓ when EVOLUTION AND CONTEMPORARY confronted by a male peer), psychologists should be in SOCIETY a position to reduce the frequency of these behaviors. A basic tenet of evolutionary psychology is that mod- One potential strategy is to provide multiple opportu- ern humans evolved domain-speciÞc cognitive abilities nities for young men to achieve status in one domain and behavioral strategies to deal with recurring condi- (e.g., athletics) or another (e.g., academics). For in- tions in the environments of our ancestors (Cosmides & stance, in this view, athletic competition is a culturally Tooby, 1994), but these abilities and strategies may not regulated expression of intrasexual competition, and always be well suited to contemporary conditions. this competition can be modiÞed (e.g., through rules) Thus, in addition to studying epigenetic processes that and channeled through athletics such that it does not guide the development of evolved social and cogni- escalate into deadly violence. tive systems, the goal of evolutionary developmental psychology is to understand how these evolved bi- CONCLUSION ases and constraints inßuence the expression and de- velopment of social and cognitive competencies that A complete understanding of human social and cog- are important in modern society. nitive development, and any associated sex differ- As an example, much of formal education is Òun- ences, requires an understanding of human evolution naturalÓ in that much of what children are taught in- and the associated epigenetic processes that guide the volves tasks never encountered by our ancestors development of evolved social and cognitive pheno- (Brown & Bjorklund, 1998; Geary, 1995). Although types. To argue otherwise is to ignore the vast empir- humans apparently have been using language for ical literature supporting DarwinÕs (1859) theory of thousands of years, it is only in this century that the evolution (e.g., Weiner, 1995) and to deny the core majority of people on the planet are literate. Geary theoretical foundation of the biological sciences. The (1995) referred to language and other evolved forms goal here was to provide a skeletal framework for of cognition, such as those represented in Figure 1, as linking the extant empirical and theoretical literatures biologically primary abilities, and skills that build upon in developmental psychology to the wider Þeld of these primary abilities but are principally cultural in- evolutionary biology and, in particular, to evolution- ventions, such as reading, as biologically secondary abil- ary developmental biology (e.g., Hall, 1992). This ities. Biologically primary abilities are acquired uni- emerging interdisciplinary Þeld of evolutionary de- versally and children typically have high motivation velopmental psychology seeks to explain not only the to perform tasks involving them. In contrast, biologi- evolutionary and biological inßuences on human de- cally secondary abilities are culturally determined, velopment, but also to understand the social and eco- and often tedious repetition and external motivation logical conditions that will necessarily affect the de- are necessary for their mastery. From this perspective, velopment and expression of social and cognitive it is understandable that many children have difÞculty competencies. In other words, an evolutionary per- with reading and higher mathematics. spective should provide a useful framework for con- Similarly, an understanding of evolved social biases ceptualizing and guiding future research across many has profound implications for understanding and ad- of the developmental specialties (e.g., social, cogni- dressing other pressing social issues, such as individual tive, and neuroscientiÞc). differences in , child neglect and abuse, the sharp increase in male-on-male violence during ad- ACKNOWLEDGMENTS olescence and early adulthood, divorce, and prejudice (e.g., Daly & Wilson, 1988). Without an appreciation of We thank Todd Shackelford and three anonymous re- the evolutionary and biological contributions to the viewers for helpful comments on an earlier draft. The epigenetic processes that shape the development of preparation of this article was supported, in part, by a these phenomena, psychology as a discipline will never Summer Research Fellowship awarded to the Þrst au- address these issues to its fullest potential. As an exam- thor by the Research Council of the University of Mis- ple, the tendency of adolescent males to engage in souri at Columbia.

64 Child Development

ADDRESSES AND AFFILIATIONS Cosmides, L., & Tooby, J. (1994). Origins of domain speciÞc- ity: The evolution of functional organization. In L. A. Corresponding author: David C. Geary, Department Hirschfeld & S. A. Gelman (Eds.), Mapping the mind: Do- of Psychology, 210 McAlester Hall, University of Mis- main speciÞcity in cognition and culture (pp. 85Ð116). New souri at Columbia, Columbia, MO 65211-2500; e-mail: York: Cambridge University Press. [email protected]. David F. Bjorklund is at Flor- Crick, N. R., & Bigbee, M. A. (1998). Relational and overt ida Atlantic University, Boca Raton, FL. forms of peer victimization: A multiinformant ap- proach. Journal of Consulting and Clinical Psychology, 66, 337Ð347. REFERENCES Daly, M., & Wilson, M. (1988). Homicide. New York: Aldine de Gruyter. Ainsworth, M. D. S., & Bell, S. M. (1970). Attachment, explo- Darwin, C. (1859). On the origin of species by means of natural ration and separation: Illustrated by the behavior of one- selection. 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