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Linked Articles: Legare, Clegg, and Wen; doi: 10.1111/cdev.13018 Bjorklund; doi: 10.1111/cdev.13020 Frankenhuis and Tiokhin; doi: 10.1111/cdev.13021

A Metatheory for Cognitive Development (or “Piaget is Dead” Revisited)

David F. Bjorklund Florida Atlantic University

In 1997, I argued that with the loss of Piaget’s theory as an overarching guide, cognitive development had become disjointed and a new metatheory was needed to unify the field. I suggested developmental biology, particularly evolutionary theory, as a candidate. Here, I examine the increasing emphasis of biology in cognitive development research over the past 2 decades. I describe briefly the emergence of evolutionary developmental psychology and examine areas in which proximal and distal biological causation have been particularly influential. I argue that developmental biology will continue to increasingly influence research and theory in cognitive development and that evolutionary theory is well on its way to becoming a metathe- ory, not just for cognitive development, but for developmental psychology generally.

Twenty years ago I published an article in Child Development titled, “In Search of a Metatheory for Cognitive Development (or, Piaget is Dead and I Don’t Feel So Good Myself),” in which I argued that the field of cognitive development had become disjointed with the demise of Piaget’s theory as a guiding light. As information-processing accounts of cognitive development began to replace Piage- tian accounts, lost were the unifying concepts of the functional invariants of assimilation and adaptation, the idea of qualitative differences in thinking between stages, and the principle of epigenesis. Although many cognitive developmentalists contin- ued to adopt these foundational ideas and apply them to topics such as theory of mind and moral development, others looked to quantitative differ- ences in basic-level information-processing mecha- nisms to explain age-related changes in children’s thinking. The result was expanding literatures on diverse topics of cognitive development, but with- out a central focus. Researchers who studied metacognition or social-cognitive development often

saw little relevance of low-level mechanisms, and those who studied basic-level processes often failed to see the scientific merit of studies of higher levels of cognitive functioning that left one feeling that the “ghost in the machine” was still in charge. I argued then that the field needed a new metatheory —a common set of broad, overarching assumptions and principles—to guide research and unify the field (Bjorklund, 1997a). I suggested that develop- mental biology could provide such a metatheory. I argued that a better understanding of brain devel- opment, for example, would be important not only from a strictly biological perspective, but also pro- vide insight into psychological development, such as the role of plasticity in ontogeny, when certain experiences are apt to be most influential, and what type of cognition should develop at what time. Although I believed that understanding biologically proximal (or immediate) influences on development would be important for understanding psychologi- cal development, I argued that the most likely can- didate for a metatheory of cognitive development would be at the distal (or ultimate) level of biologi- cal causation, evolutionary theory.I would like to thank Carlos Hern�andez Blasi, Kayla Causey,

Karin Machluf, Alyson Myers, Patrick Douglas Seller, II, and three anonymous reviewers for helpful comments on earlier drafts of this article.

Correspondence concerning this article should be addressed to David F. Bjorklund, Department of Psychology, Florida Atlantic University, Boca Raton, FL 33431. Electronic mail may be sent to [email protected].

© 2018 The Authors Child Development © 2018 Society for Research in Child Development, Inc. All rights reserved. 0009-3920/2018/8906-0027 DOI: 10.1111/cdev.13019

Child Development, November/December 2018, Volume 89, Number 6, Pages 2288–2302

There has been a steady biologizing of develop- mental psychology over the past 2 decades. In this article, I first review briefly research and theory of proximal biological causes on cognitive develop- ment, including developmental cognitive neuro- science, behavioral genetics, and epigenetics. Despite the increase in cognitive developmental research from a proximal biological perspective, I do not believe this rises to the level of a new metatheory. Rather developmental biology repre- sents a discipline (or subdiscipline) of study and is too broad to serve as an effective metatheory.

In the latter sections of this article, I propose that evolutionary developmental psychology is a better candi- date for a metatheory for cognitive development. Evolutionary developmental psychology is “the study of the genetic and ecological mechanisms that govern the development of social and cognitive com- petencies common to all human beings and the epi- genetic (gene–environment interactions) processes that adapt these competencies to local conditions” (Geary & Bjorklund, 2000, p. 57). Proponents of evo- lutionary developmental psychology view cognitive development as a natural consequence of species- typical behavior in a species-typical environment that evolved to solve certain problems associated with survival. It assumes that natural selection has operated on the early stages of development as well as (or more than) the adult stages. Along these lines, evolutionary developmental psychology assumes that some immature features of infancy and child- hood are (functional) adaptations to that time in development and not necessarily cognitive short- comings that need to be overcome (Bjorklund, 1997b). In fact, I believe that, whether anyone noticed it or not, the field of cognitive development has implicitly adopted a new evolutionarily based metatheory.

Proximal Biological Causation: Developmental Cognitive Neuroscience, Genetics, and Epigenetics

Since the 1980s, child developmentalists have increasingly looked at the biological roots of onto- geny, including the effect of hormones on behavior, behavioral genetics, and molecular genetics (see Johnson, 2015). This increased interest in the biol- ogy of development has resulted in more sophisti- cated ways of conceptualizing the classic nature/ nurture debate. Developmental psychologists no longer ask how much of any phenotypic outcome is due to nature and how much is due to nurture, but

rather examine gene–environment interactions (or transactions) and ask how genes and environment interact to produce patterns of development.

Perhaps the most obvious impact of biology on cognitive developmental psychology in the past 20 years is the emergence of developmental cogni- tive neuroscience, although research in behavioral genetics, and more recently epigenetics, has also caught the attention of developmental psychologists.

Developmental Cognitive Neuroscience

Byrnes and Fox (1998) predicted a revolution in developmental psychology equivalent to the cogni- tive revolution that replaced behaviorism as the principle metaphor of psychology: developmental cognitive neuroscience. Since then new techniques of brain imaging have resulted in an explosion of research focusing on the study of typical and atypi- cal cognitive and neurological development (e.g., Marshall, 2015). Neuroscience research has pro- vided insight into the development of executive functions, memory, face perception, language, psy- chometrically measured intelligence, theory of mind, and self-awareness, among many other topics (see Johnson, 2011). Developmental cognitive neuro- science research has shown how early environmen- tal deprivation affects the development of particular parts of the brain, identified patterns of recovery of function from brain damage, as well as provided insights into developmental disorders such as atten- tion deficit hyperactivity disorder, autism, and reading disabilities (see Marshall, 2015).

Psychologists have long known that the brain is the seat of cognition, and merely having images in which different sections of brains light up provides little new insight into cognitive functioning or devel- opment. The best neuroscience research not only identifies areas of the brain associated with a partic- ular type of cognition but, combined with behavioral data, provides insight into the psychological mecha- nisms involved. For example, it is well established that the hippocampus plays a central role in the acquisition of new declarative memories, and evi- dence that adults with hippocampal damage show deficits in deferred imitation (McDonough, Mandler, McKee, & Squire, 1995) suggests that it is supported by nonverbal declarative/explicit memory. Neuro- science research examining the development of the prefrontal cortex, the hippocampus, and the dentate gyrus (part of the hippocampus) is consistent with behavioral evidence of the development of deferred imitation in infancy, providing strong support that

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deferred imitation is indeed an early form of nonver- bal declarative memory (e.g., Bachevalier, 2014). These findings go beyond simply highlighting which areas of the brain light up under certain task condi- tions but provide neurological evidence in support of behavioral data and psychological theories.

Behavioral Genetics and Epigenetics

New developmental behavioral genetic research has also contributed to our understanding of devel- opment over the past 2 decades. Behavioral genetics examines the degree to which individual differences in some behavioral or psychological trait can be attributed to genes versus environment. For exam- ple, Caspi et al. (2007) identified two alleles of a gene located on chromosome 11 associated with the processing of fatty acids. Earlier research had reported that children, adolescents, and adults who were breastfed as infants had higher IQs than those who were bottle-fed (Moretensen, Michaelsen, San- ders, & Refnisch, 2002). In two large samples, Caspi and his colleagues reported that children who had two variants of the alleles (called CC and CG) and were breastfed as infants had statistically higher IQs (approximately 104) than children who had the same set of alleles but were not breastfed (approxi- mately 97). There was no difference in IQ between children who were breastfed or not as infants who had a third combination of alleles (GG; both groups had IQs of about 100). Thus, the effect on IQ of breastfeeding is associated with a particular combi- nation of alleles for a gene related to how a person processes fatty acid, illustrating that even genes known to be associated with specific biochemical and behavior outcomes (here, high IQ) are expressed differently in different environments (here, breastfed vs. bottle-fed). This effect is some- what elusive, in that a follow-up study reported that children with the GG genotype displayed the greatest discrepancy as a function of feeding method (not the least as in Caspi et al.’s findings), with bottle-fed GG children having the lowest ver- bal IQ scores (Steer, Davey Smith, Emmett, Hib- beln, & Golding, 2010). Such findings indicate that pinpointing the effect of any single set of genes/al- leles on cognitive development may be difficult, but with increasing sophistication in both identifying genes associated with cognitive measures and quan- titative analyses, future research may better eluci- date the relations between genes and children’s developing cognitive abilities.

In other behavioral genetic research, the heritabil- ity of IQ was shown to vary as a function of

socioeconomic status (e.g., Rowe, Jacobson, & van der Oord, 1999). For example, although the heri- tability of IQ in a large sample of adolescents and their relatives was found to be .57 and the influence of shared environment was .13, these values varied significantly when level of parental education was considered. Heritability increased to .74 and the effect of shared environment decreased to .00 for adolescents from more highly educated families; the pattern was reversed for adolescents from less-edu- cated families, with heritability decreasing to .26 and the effect of shared environment increasing to .23 (Rowe et al., 1999). These results reflect the fact that heritability is a population statistic and does not represent a stable, biological property of indi- viduals, but varies depending on the population under study and aspects of the environment that influence a trait. Once a certain level of environmen- tal support for intellectual development is estab- lished (i.e., a threshold), as reflected by homes in which parents have higher levels of education, indi- vidual differences in environments matter relatively little, as individual differences in genetics become manifest. In contrast, for homes that do not provide high levels of environmental support for cognitive development, as reflected by homes in which par- ents have lower levels of education, individual dif- ferences in environments have greater influence on IQ and genetics less.

Despite the demonstration of gene–environment effects in these and other behavioral genetic stud- ies, many developmental psychologists view such research skeptically, believing that the parceling of genetic and environmental influences misrepresents gene–environment effects. The proper question is how do genes and all other elements and pro- cesses external to the genes interact (or transact) to produce a particular pattern of development (e.g., Moore, 2015). For many, the behavioral genetic approach remains inherently nondevelopmental. New research in epigenetics, however, is providing avenues for biologically minded developmentalists.

Moore (2015) describes epigenetics as “how genetic material is activated or deactivated—that is, expressed—in different contexts” (p. 14). Plants and animals inherit not only genes, but also chemical markers that regulate the expression of genes. For instance, early in development, genes are “turned on,” influencing construction of major parts of an organism (e.g., the development of fingers and toes). Once fingers and toes, for example, are constructed, those genes are “turned off” via chemical markers, with methylation being the most studied and best understood epigenetic mechanism. When chemicals

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from the methyl group (written CH3) attach to a por- tion of DNA, they influence whether and how much protein a gene will produce. Recent research has shown that methylation occurs not only during early development, but throughout life and may be one mechanism by which experience alters behavior and psychological development. For example, research by Meaney (2013) has shown that the licking patterns of mother rats toward their pups are associated with the pups’ subsequent stress response and their behavior toward their own pups when they become mothers. These effects are associated with epigenetic (methylation) changes that are transmitted across generations without changing the genes themselves. Although in mammals most epigenetic markers that occur during a parent’s lifetime are erased in their offspring soon after fertilization, some apparently are not, as indicated by evidence of the effects of early malnutrition on the subsequent metabolism of women’s and men’s grandchildren (see Moore, 2015).

Researchers have recently investigated epige- netic effects in human children. For example, research using placental blood (Kertes et al., 2016) or saliva (Parades, Ridout, et al., 2016) has shown that early stress is related to the methylation of genes associated with the expression of the stress hormone cortisol and to subsequent internalizing behavior. Other research has shown that 11- to 14- year-old children who had been maltreated display greater methylation to a gene associated with stress regulation and to a gene associated with nerve growth factor than nonmaltreated children (Romens, McDonald, Svaren, & Pollak, 2015). It is not known whether these effects might aid chil- dren in adapting to difficult environments or con- tribute to mental and physical disorders, but they do clearly show a chemical mechanism for how experience affects gene expression and possibly subsequent behavior. Although I am not aware of specific epigenetic studies that are directly related to cognitive development, I suspect that cognitive developmental researchers in the near future will avail themselves to these new techniques and examine the effects of early experience on later cognitive and intellectual functioning from an epi- genetic perspective.

Distal Biological Causation: Evolutionary Perspectives on Cognitive Development

Although new research and theory in neuro- science and epigenetics are changing developmental

psychologists’ views of the role of biology on onto- geny, evolutionary perspectives have had an even greater influence on scholarship in cognitive devel- opment over the past 20 years. Evolutionary theory is the foundation of modern biology and is becom- ing the foundation of modern psychology and of developmental psychology. To quote anthropologist Konner (2010), “Nothing in childhood makes sense except in the light of evolution.”

The Emergence of Evolutionary and Evolutionary Developmental Psychology

Mainstream evolutionary psychology emerged as a new discipline in the 1980s and 1990s (e.g., Tooby & Cosmides, 1992). It emphasized a gene’s eye view of behavior, proposing that adaptive evolution occurs via the differential survival of competing genes, and proposed that domain-specific, evolved information-processing mechanisms (i.e., mecha- nisms used to solve problems in particular domains), shaped by natural selection to solve recurrent prob- lems faced by our ancestors, were the missing link in evolutionary explication. These implicit mecha- nisms were activated in appropriate environmental contexts to deal with problems of survival, mating, and social interactions. For many developmentalists, such evolved and inherited mechanisms had the stain of genetic determinism (e.g., Witherington & Lickliter, 2016), the antithesis of a true developmen- tal perspective. In fact, most evolutionary psycholo- gists paid little attention to development in their theorizing, treating it as an epiphenomenon—of great significance to the individual, but of no conse- quence to the evolution of the species.

Around the turn of the 21st century, a number of developmental psychologists began to apply evolu- tionary concepts to the study of human develop- ment, proposing that some characteristics of infants and children were selected to adapt them to a speci- fic time in development and not to prepare them for adulthood (e.g., Bjorklund, 1997b; Hern�andez Blasi & Bjorklund, 2003), and that evolved, adaptive behavior emerged following tenets of developmental systems theory (e.g., Gottlieb, 2000), avoiding notions of genetic determinism (Geary & Bjorklund, 2000).

Plasticity as an Evolved Feature of Infancy and Childhood

In the years since these early proposals, scholars with an evolutionary developmental perspective have emphasized that plasticity itself has been the focus of natural selection, enabling the developing

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organism to adjust its behavior to the demands of the local environment within evolved constraints (see Bjorklund & Ellis, 2014; Del Giudice & Ellis, 2016). For example, in her book, The Gardner and the Carpenter: What the New Science of Child Development Tells us About the Relationship Between Parents and Children, Gopnik (2016) argues that:

development plays a crucial role in explaining human nature. The old “evolutionary psychol- ogy” picture was that genes were directly resp- onsible for some particular pattern of adult behavior—a “module.” However, there is more and more evidence that genes are just the first step in complex developmental sequences, cas- cades of interactions between organism and envi- ronment that in turn shape the adult brain. Even small changes in developmental timing can lead to big changes in who we become. (p. 208)

Evolutionary developmental psychology also departs from mainstream evolutionary psychology in the use of the concept of “innateness” and the related concept of “instinct,” in large part because they are ill defined, and once an ability or behavior is labeled innate (or instinctive), it stops further examination of its origin (Bateson, 2002; Samuels, 2004). This is illustrated by Bateson (2002), who wrote of the term “instinct”:

Apart from its colloquial uses, the term instinct has at least nine scientific meanings: present at birth (or at a particular stage of development), not learned, developed before it can be used, unchanged once developed, shared by all mem- bers of the species (or at least of the same sex and age), organized into a distinct behavioral systems (such as foraging), served by a distinct neural module, adapted during evolution, and differences among individuals that are due to their possession of different genes. One does not necessarily imply another even though peo- ple often assume, without evidence, that it does. (P. 2212)

Given the vagueness of this term and the rejec- tion of a genetically deterministic perspective of evolution, from an evolutionary developmental per- spective, children are not so much born with instincts, but rather with low-level cognitive and perceptual abilities, or cognitive primitives (Samuels, 2004), that develop into adaptive behav- ior and cognition when they experience a species-

typical environment, although theorists vary in the extent to which they believe inherited abilities ver- sus experience constrain development. For example, a major perspective within developmental cognitive neuroscience is neuroconstructivism, which postu- lates that, beginning in infancy, neural structures and functions emerge as a result of dynamic inter- actions between brain systems and “expected” envi- ronments (i.e., environments that most members of a species can expect to experience) to produce spe- cies-typical patterns of cognitive development. Neu- roconstructivist theorists argue for relatively weak constraints and place greater emphasis on experi- ence in shaping behavior and cognition (e.g., New- combe, 2011). In contrast, neonativists argue that innate capacities organize/constrain cognitive struc- ture and function relatively independent of experi- ence, at least early in development (e.g., Spelke & Kinsler, 2007). Taking a somewhat middle position, Geary (2005) argues that constraints should be weaker (and the effect of experience greater) when ancestral environments associated with an ability were more heterogeneous, thus requiring variable responses from the developing organism, and stron- ger when ancestral environments associated with an ability were more homogeneous. Geary pro- posed that infants are born with skeletal competen- cies, information-processing constraints or biases that are fleshed out over the course of ontogeny primarily through play.

Along similar lines, my colleagues and I pro- posed that adaptations develop as a result of early perceptual and cognitive biases interacting with maturationally paced neural development in a spe- cies-typical environment (Bjorklund, 2015; Bjork- lund & Ellis, 2014; Bjorklund, Ellis, & Rosenberg, 2007). More specifically, and consistent with the tenets of developmental systems theory, Bjorklund et al. (2007) defined evolved probabilistic cognitive mechanisms as:

information-processing mechanisms that have evolved to solve recurrent problems faced by ancestral populations; however, they are expressed in a probabilistic fashion in each indi- vidual in a generation, based on the continuous and bidirectional interaction over time at all levels of organization, from the genetic through the cultural. These mechanisms are universal, in that they will develop in a species-typical manner when an individual experiences a species-typical environment over the course of ontogeny. (p. 22)

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For example, infants are not born with a fear of snakes, although like adults, they more easily iden- tify snakes embedded in a background of flowers and mushrooms than vice versa (e.g., LoBue & DeLoache, 2010), and 9-month olds are more atten- tive to photographs of snakes, as reflected by pat- terns of evoked potentials, than to photographs of neutral stimuli (Hoehl & Pauen, 2017). Infants also more readily learn an association of a fearful voice to videos of snakes than to other potentially dan- gerous animals, but not to still photographs of snakes (DeLoache & LoBue, 2009). Apparently, infants are prepared by natural selection to be attentive to the snake’s unique sinusoidal move- ment and to associate such movement with a fear- ful voice. Such observations make it unnecessary to propose a fear of snake instinct or an isolated mod- ule. Similarly, infants possess low-level perceptual biases to attend to physical stimuli that have many of the features of primate faces (e.g., top-heavy con- figuration, vertical symmetry, eye spots), and can initially discriminate among faces of different spe- cies, sexes, and races equally well. With increasing experience, perceptual ability narrows, so that by 9 months infants are increasingly able to discrimi- nate among faces from their own race, for example, but no longer among faces from other races (Kelly et al., 2009), unless they have also been exposed to faces from other races (Anzures et al., 2012). Such adaptations are not inevitable and will not emerge if children experience a species-atypical environ- ment (e.g., frequently seeing monkey faces, Pascalis et al., 2005).

Much developmental research performed by evo- lutionarily minded scientists can be interpreted in terms of evolved probabilistic cognitive mecha- nisms, even if the researchers themselves had not explicitly adopted the concept (Bjorklund, 2016). However, evolutionary developmental psychology is not monolithic, with some researchers adopting a perspective perhaps more compatible with main- stream evolutionary psychology than with the per- spective presented here. What is undeniable is that evolutionary thinking has seeped into the minds of many cognitive developmental psychologists, and I review briefly some of this research in the following section.

Evolutionarily Informed Research in Cognitive Development

There are a number of areas within cognitive development where evolutionary thinking has become especially prominent, leading to new dis-

coveries and interpretations of cognitive develop- ment. These include aspects of infants’ object repre- sentation, social-cognitive development, tool use, brain development sex differences in cognitive abili- ties, research into the role of early experience on later development, among others (see reviews in Bjorklund, 2015; Bjorklund & Ellis, 2014). Let me briefly outline research in three such areas: social cognition, particularly social learning, the role of experience on later development, and the adaptive value of immature cognition.

Developing the Sociocognitive Brain

When Piaget was king, researchers examining social-cognitive development held the implicit (often explicit) assumption that a child could only be as social as his or her level of cognitive ability allowed. In other words, cognitive ability, whether defined in terms of Piagetian-like schemes or information- processing mechanisms, was foundational to social behavior and cognition: “Soft” social cognition was derivative of “hard” cognition. For example, chil- dren’s egocentricity limited their ability to take the perspective of others, their understanding of conser- vation affected their understanding of the constancy of gender, and their ability to encode and interpret social stimuli determined the efficacy of their social behavior.

Evolutionary theorists have turned this viewpoint on its head. Rather than seeing nonsocial cognition as the foundation for social cognition, a number of theorists have proposed that human cognitive abili- ties evolved primarily to deal not with the physical world but with conspecifics. This social brain hypothe- sis (e.g., Dunbar, 2003) emphasizes the importance of learning to cooperate and compete with fellow humans and that infants and children have been pre- pared by natural selection to process social informa- tion especially well. Rather than starting with the assumption that children’s abilities to make sense of their physical world determines their level of social understanding and behavior, researchers with an evolutionary developmental perspective look to chil- dren’s immediate social environment and ask what skills or understanding they require to function effec- tively with other people, some of whom are caretak- ers and others who are peers whom they will cooperate and compete with and learn from. For example, infants from the earliest days are biased to attend to biological movement (e.g., Bardi, Regolin, & Simion, 2014) and face-like stimuli (e.g., Mondloch et al., 1999). They come to view others as intentional agents, individuals who act purposefully to achieve

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some goal, sometime during their 1st year, as reflected by shared attention (Tomasello & Carpen- ter, 2007), which is vital for learning from observa- tion and teaching.

Beginning around 3 years of age, children engage in overimitation, copying not only task-rele- vant aspects of a model’s behavior but irrelevant ones as well (e.g., Nielsen, 2006). Moreover, when children copy both relevant and irrelevant actions of a model, they believe it is normative—it is what one is supposed to do, and they will correct a pup- pet, for example, for skipping irrelevant actions (Kenward, 2012). Although such overimitation can be seen as a cognitive limitation and a reflection of an immature nervous system, it is better viewed as an evolved adaptation for learning about cultural artifacts and their uses (Csibra & Gergely, 2011). Children may later learn more efficient means of solving problems, but their tendency to copy faith- fully all the actions of a proficient model, in more cases than not, leads to acquiring culturally appro- priate practices.

The Effects of Early Experience on Development

The effect of early experience on later develop- ment is a staple of mainstream developmental psy- chology, but it also has become an important topic in evolutionary developmental psychology. From a predictive adaptive response account, children possess substantial cognitive and behavioral plasticity that permits them to sample their current environment and alter aspects of their developmental trajectory in anticipation of future environments. In an early article along these lines, Belsky, Steinberg, and Draper (1991) proposed that

a principal evolutionary function of early experi- ence—the first 5–7 years of life—is to induce in the child an understanding of the availability and predictability of resources (broadly defined) in the environment, of the trustworthiness of others, and of the enduringness of close interper- sonal relationships, all of which will affect how the developing person apportions reproductive effort. (p. 650)

Since the publication of this seminal article, researchers have longitudinally examined people’s reactions to childhood environments that varied in harshness and predictability, mostly following the principles of life-history theory. Life-history theory is a general framework that examines decisions organ- isms make in allocating time and energy to various

aspects of their development from the perspective of natural selection. Depending on ecological condi- tions, how many resources should be devoted to somatic growth versus reproduction, for example, and how much effort and energy should be devoted to current development (or reproduction) versus later development (or reproduction)? Some life-history theorists propose that children growing up in harsh and unpredictable environments will adopt a fast life-history strategy, reaching sexual maturity and beginning sexual activity early, estab- lishing unstable pair bonds, and investing less in their offspring, all in comparison to children grow- ing up in supportive and predictable environments, who should adopt a slow life-history strategy (Ellis, Figueredo, Brumbach, & Schlomer, 2009). This pattern has been found in numerous studies (e.g., Nettle & Cockerill, 2010; Simpson, Griskevicius, Kuo, Sung, & Collins, 2012). Most accounts propose that this adaptive pattern evolved because early environments are predictive of later environment (“external predictive model”). However, an alterna- tive account, supported by mathematical models (Nettle, Frankenhuis, & Rickard, 2013), proposes that early-life adversity negatively affects health and longevity, making it adaptive for individuals to adjust important aspects of somatic development (“internal predictive model”) in anticipation of a short life (e.g., Bergh€anel, Heistermann, Sch€ulke, & Ostner, 2016). The external and internal accounts are not necessarily mutually exclusive, but the use of mathematical models requires researchers to make more precise the conditions under which predictive adapted responses should occur, as well as the mechanisms underlying the phenomenon (e.g., Nettle et al., 2013).

Although most research to date performed from a life-history perspective has focused on topics typically associated with social and emotional development, some studies have examined aspects of cognitive development. For example, Mittal, Griskevicius, Simpson, Sung, and Young (2015) pro- posed that the harshness and predictability of early rearing environments would have different conse- quences for different aspects of executive function. They proposed and found that people who experi- ence harsh and unpredictable early environments would show deficits in inhibition, but be better at task shifting (a type of cognitive flexibility) relative to people who experienced less harsh and more stable early environments. Mittal et al. reasoned that, although inhibition is vital for attaining long- term goals, it can be disadvantageous when ecolog- ical conditions favor opportunism. In contrast, the

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ability to shift effectively between tasks is critical for adapting to unpredictable environments. Although a fast life-history strategy involves greater aggressive and risky behavior, often with poor mental health outcomes, from an evolutionary per- spective it represents potentially adaptive outcomes for children growing up in harsh and unpredictable circumstances (Ellis, Bianchi, Griskevicius, & Frankenhuis, 2017; Ellis et al., 2009). Surviving in an uncertain environment likely requires prioritizing short-term success over what is best in the long term, allowing for the selection of these adaptations.

How does an evolutionary developmental per- spective of the effects of early experience as described here differ from conventional viewpoints? Within mainstream developmental and clinical psy- chology the dominant scientific paradigm for explaining the relation between detrimental, high- risk environments and subsequent outcomes is the mental health model (also called the diathesis–stress model). According to this model, harsh and unpre- dictable early environments forecast negative out- comes, such as insecure attachment, sexual promiscuity, and academic and economic failure, whereas supportive and predictable environments forecast positive outcomes. With respect to early harsh environments, the mental health model focuses primarily on the costs to children, ignoring the potential adaptive benefits. In contrast, evolu- tionary developmental perspectives based on vari- ants of life-history theory emphasize that early development is not so much disturbed by stressful environments as it is directed or regulated toward achieving adaptive strategies to function later in life in these harsh environments (see Del Giudice & Ellis, 2016; Ellis et al., 2017). Taking an evolutionary developmental perspective of the consequences of harsh early environments on later outcomes causes us to view development differently than when tak- ing a mental health model view. Although insecure attachment, early sexual debut, and academic fail- ure are appropriately seen as maladaptive from a societal (and mental health model) perspective, they are viewed as adaptive responses to stressful envi- ronments from an evolutionary perspective, and such a viewpoint influences not only the research questions scientists ask, but also the social policies aimed at these problematic behaviors.

The Adaptive Value of Cognitive Immaturity

Piaget taught us that children’s thinking is not simply a less-effective version of the thinking of

adults, but that children’s cognition at different ages/stages has an integrity of its own. Although one can dispute the degree to which developmental changes in cognition are continuous or discontinu- ous in nature, few developmental scientists today argue that children’s thinking is simply adult think- ing in miniature. Evolutionary developmental psy- chology extends this perspective, proposing that some aspects of infancy and childhood, rather than being preparations for adulthood, are instead designed by natural selection to adapt the child to its current environment, not necessarily to a future one, and are referred to as ontogenetic adaptations (Bjorklund, 1997b; Oppenheim, 1981). From this perspective, some forms of cognitive immaturity represent not mental shortcomings that should be overcome the sooner the better, but rather adapta- tions that help children deal with current contexts.

Ontogenetic adaptations can be seen in the earli- est periods of postnatal life. For example, Meltzoff and Moore (1977) identified newborns’ tendency to copy the facial expressions of adult models (neona- tal imitation) as an early form of social learning. In contrast, proponents of evolutionary developmental psychology hypothesized that such “imitation” is not a form of social learning but rather a reflexive- like behavior serving to promote social interaction between an infant and its mother during a time when the infant cannot control its own social behavior (Bjorklund, 1987). Consistent with this position is evidence that such imitation declines to chance levels by about 2 months of age (e.g., Jacob- son, 1979), and that newborns who show elevated levels neonatal imitation displayed better social interactions with their mothers 3 months later (Hei- mann, 1989). More recent research has challenged the selective imitation of facial gestures in neonates (Jones, 2009; Oostenbroek et al., 2016). Jones (2009), for example, demonstrated that infants made facial gestures to a wide range of stimuli (e.g., flashing lights, a looming black pen, music) and proposed rather than reflecting true imitation, neonatal imita- tion is a young infant’s response to interesting or arousing stimuli. In a longitudinal study, Oosten- broek et al. (2016) assessed infants’ responses to a broad range of stimuli and concluded that babies do not show selective matching of facial gestures as proposed by Metlzoff and Moore. However, inspec- tion of Oostenbroek et al.’s data (figure 2, p. 3) indicates that although infants do not consistently match the facial gestures of a model (e.g., tongue protrusion when shown tongue protrusion), they do consistently display some facial gesture in response to tongue protrusion or mouth opening.

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Such responses, although not qualifying as imitative behaviors, would serve to maintain social interac- tions between mothers and infants, consistent with the interpretation that the phenomenon described by Meltzoff and Moore is an ontogenetic adaptation.

Immature cognition has even been suggested as a contributor to young children’s language acquisi- tion. For example, Newport (1991) proposed the less-is-more hypothesis, suggesting that cognitive limi- tations of infants and young children simplify the corpus of language they process, making the com- plicated syntactical system of language easier to learn. Newport’s theory is an extension of Turke- witz and Kenny’s (1982) proposal that perceptual limitations in infancy are adaptive, in that they per- mit one sensory system to develop (e.g., hearing) without having to compete for neural resources with another later developing system (e.g., vision). Newport noted that children in the early stages of language acquisition begin slowly—more slowly than adults do when learning a second language. To test her hypothesis, Newport developed a com- puter simulation that varied the amount of input that could be kept in memory at any one time. She reported that with a less restricted filter (reflecting a larger short-term store), many language-irrelevant associations were retained, which hindered rather than facilitated language learning. Newport (1991) concluded,

Overall, then, a learning mechanism with a restricted input filter more successfully acquired a morphology; the same learning mechanism with a less restricted filter, or with no filter at all, entertains too many alternative analyses and can- not uniquely determine which is the better one. (p. 127)

Elman (1994) reached a similar conclusion using a different type of computer simulation (his meta- phor was “the importance of starting small”), and consistent with both Newport’s and Elman’s hypotheses, subsequent research demonstrated that adults learn an artificial grammar faster when pre- sented with smaller units of the language (Kersten & Earles, 2001). Adults further play a role in facili- tating language acquisition by typically speaking to infants and young children using highly repetitive and greatly simplified child-directed speech (e.g., Fernald, 1992). According to Bjorklund and Schwartz (1996), “Such modified language, accom- panied with young children’s limited information- processing abilities, results in children receiving a

much reduced body of linguistic evidence from which to extract the phonological, syntactic, and semantic rules of their mother tongue” (p. 26).

Other examples of preschool-age children’s immature cognition having adaptive value can be seen in their self-centered perspective, their ten- dency to attribute purpose or design to objects and events, and their overestimation of their abilities. A classic characteristic of Piaget’s stage of preopera- tions, egocentricity results in young children refer- encing objects and events to themselves, which enhances their memory of those objects and events (e.g., Ross, Anderson, & Campbell, 2011). Preschool children also readily assume that both artifacts and natural phenomena were designed for specific pur- poses, which Kelemen (2004) refers to as promiscu- ous teleology. Although often resulting in humorous statements, such as mountains are “for climbing,” it also results in children believing that tools were made for specific purposes (the design stance), and although this sometimes results in inflexible use of artifacts (i.e., functional fixedness), it also produces rapid acquisition of tool use (e.g., Casler & Kele- men, 2005). According to the Casler and Kelemen (2005), “young children exhibit rapid learning for artifact function, already possessing an early foun- dation to some of our most remarkable capacities as tool manufacturers and users” (p. 479). With respect to overestimating one’s own abilities, young children are the optimists of the world, believing they possess greater abilities, qualities, and perfor- mance than an objective assessment would suggest. Rather than reflecting a metacognitive deficit, for young children in some contexts, it is associated with higher verbal IQ and enhanced performance on later trials of cognitive tasks (see Bjorklund, Periss, & Causey, 2009 for a review). Young chil- dren’s overly optimistic assessments of their own abilities presumably enhance their self-efficacy (Bandura, 1997), causing them to persist on tasks and in situations where a child with a more accu- rate evaluation of his or her performance might quit.

As a final example of the adaptive value of immature cognition, consider play. The topic of play has not been ignored by developmental psy- chologists (e.g., Pellegrini, 2013), although in the absence of an evolutionary perspective its role in cognitive development has been underplayed. Play characterizes the behavior of children, declines with age (though seemingly never disappears in humans), and is observed in most juvenile social mammals. Comparative psychologists have long acknowledged that play has both immediate and

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deferred benefits for a young organism. According to Millar (1969), “If animals play, this is because play is useful in the struggle for survival; because play practices and so perfects the skills needed in adult life.” Across cultures, children spend between 10 and 40% of their time in various forms of play (see Pellegrini, 2013). In traditional cultures, where adults engage in little direct teaching of children, most culturally important skills are acquired via observation in the context of play (Lancy, 2015). In fact, Nielsen (2012) proposed that fantasy play and imitation were central features of human childhood that had critical roles in the evolution of human cognition. According to Nielsen (2012), “By pre- tending children thus develop a capacity to gener- ate and reason with novel suppositions and imaginary scenarios, and in so doing may get to practice the creative process that underpins innova- tion in adulthood” (p. 176).

Recognizing that play evolved as a means for young animals to acquire important physical, social, and cognitive skills, puts play in a different light than it has customarily been viewed. While play has been disappearing from schools over recent decades, evolutionarily oriented psychologists and educators have recognized its importance and rec- ommended its reintroduction to the school curricu- lum (e.g., Toub, Rajan, Golinkoff, & Hirsh-Pasek, 2016). Contemporary cognitive developmental research supports these arguments. For example, some research has found a positive relation between playing and language development, per- spective taking, and executive function abilities (e.g., Berk, Mann, & Ogan, 2006; Pierucci et al., 2014). In two retrospective studies, the amount of free play adults reported engaging in during child- hood was positively associated with social success (e.g., self-esteem, friendships, psychological health, physical health; Greve & Thomsen, 2016; Greve, Thomsen, & Dehio, 2014), with subsequent analyses revealing that the benefits of childhood free play on adult outcomes were mediated by enhanced adap- tivity (flexible goal adjustment). Children’s play may be childish and a reflection of immaturity, but it is far from frivolous; rather, it is a reflection of adaptive processes that played a role in human phylogeny and continues to be important for human ontogeny.

It is not news that children get smarter with age. An evolutionary developmental perspective, how- ever, does not view this transition as the simple replacement of poor cognition with good. Rather, some aspects of immature cognition are adaptive in their own right, well suited to a particular time in

development, and possibly being necessary steps in the acquisition of more advanced cognitive skills and accomplishments.

Closing Remarks

In all organisms, natural selection operates more strongly before adulthood than after it, or, in the words of life-span psychologist Baltes (1997), “the benefits resulting from evolutionary selection evince a negative age correlation” (p. 367). Based on mod- ern hunter-gatherers, it is estimated that approxi- mately 50% of ancestral children died by their fifth birthdays, making infancy and childhood the “cru- cible for natural selection” and childhood an ideal place to test-out evolutionarily influenced hypothe- ses (Volk & Atkinson, 2013).

I realize that not all cognitive developmental psychologists embrace an evolutionary perspective, and others, while acknowledging the importance of integrating evolution and development, reject some of the core assumptions of a Darwinian approach to development (e.g., Witherington & Lickliter, 2016). Others outright reject evolutionary interpreta- tions of psychological development, suggesting they are no more than “just so stories,” without scientific merit. Yet, evidence from a variety of sources converges on the interpretation that evolutionary processes have influenced children and their devel- opment. For example, animal comparative studies illustrate both cognitive similarities (e.g., under- standing of the physical world) and differences (e.g., social cognition) between our closest genetic relatives, chimpanzees (Pan troglodytes), and pre- school children (e.g., Herrmann, Call, Hern�andez- Lloreda, Hare, & Tomasello, 2007); cross-cultural studies reveal universal features in important domains such as social learning (e.g., Nielsen & Tomaselli, 2010) and tool use (e.g., Nielsen, Mushin, Tomaselli, & Whiten, 2014); and mathematical mod- els on a variety of evolutionarily relevant topics, including sensitive periods (Fawcett & Frankenhuis, 2015), life-history theory (Nettle et al., 2013), and developmental systems theory as applied to evolu- tion (e.g., Frankenhuis, Panchanathan, & Barrett, 2013), among others, provide means of contrasting different evolutionary developmental hypotheses.

It seems irrefutable that the field of cognitive development has become increasingly influenced by theory and research from developmental biology over the past 20 years. Yet, does such a shift in emphasis rise to the level of a new metatheory for cognitive development? In themselves, the

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biologically informed approaches do not constitute qualitatively new ways of describing cognitive development. The cognitive revolution provided new ways to think about children’s thinking that differed both from Piaget’s emphasize on assimila- tion, accommodation, equilibration, and cognitive schemes and from learning theories that emphasized operant and classical conditioning (see Stevenson, 1972). Contemporary developmental neuroscience and evolutionary developmental approaches con- tinue to describe children’s thinking and its develop- ment in terms of cognitive mechanisms, not so different from those used by cognitive and social- cognitive developmentalists in the last century.

Yet, I argue that evolutionary-oriented research and theory does, in fact, constitute a new metathe- ory for cognitive development, ones that reflect not so much a change in the psychological mechanisms that underlie cognitive development, as a change in emphasis in what constitutes important functions worthy of study and how cognitive development is understood. With respect to evolutionary theory, it is concerned with a handful of core issues that will remain relevant long after more specific psychologi- cal theories are forgotten: survival (e.g., acquiring a fear of snakes), mating (e.g., adolescent dating behavior), kin (e.g., parent–child relationships), understanding the physical world and artifacts (e.g., tool use), and social relationships (e.g., cooper- ating and competing with conspecifics). Evolution- ary developmental psychology does not view children as being equipped with innate mechanisms within these domains, but rather with cognitive mechanisms such as attention, memory, and reason- ing designed by natural selection to be sensitive to environmental conditions that are used to learn to solve problems to foster survival; and these mecha- nisms, and the adaptations they promote, develop (Bjorklund, 2015).

Moreover, evolutionary theory does not replace proximal accounts of cognitive development, but rather serves as an overarching, distal-level perspec- tive, identifying important topics that can help developmental scientists ask better research ques- tions. An increasing number of cognitive develop- mental researchers, if not actually becoming evolutionary psychologists, are incorporating evolu- tionary thinking into their theories or interpretation of their data. This is reflected by Gopnik (2009) in her extensive (and highly accessible) review of research and theory from the emerging field of developmental cognitive science, who concluded “ultimately, the new scientific explanations of child- hood are rooted in evolutionary theory” (p. 7).

In 1997, I argued that having an overarching metatheory of cognitive development based on evolutionary theory will help us ask better ques- tions and collect data that will remain relevant even after the specific psychological theory that generated the data has been forgotten. As I wrote then, “By adopting a metatheory that views cognitive development as a natural consequence of species-typical behavior in a species-typical envi- ronment that evolved to solve certain problems, we will make progress. We will ask better ques- tions and collect better data” (p. 147). In some sense, this is what Piaget did. Despite the loss of ardent followers of his theoretical account, Piaget’s research findings remain relevant today, in part, because he studied universal aspects of cognitive development, mainly children’s understanding of physics—from object permanence, to conservation, to time and space.

Cognitive developmental psychologists taking an evolutionary perspective have made substantial advances in understanding human ontogeny over the past 2 decades and, coupled with cognitive developmental research looking at biologically proximal causes (neuroscience, epigenetics), this trend is likely to continue in the near future. Although this shift may be most prominent for cog- nitive development, I believe that evolutionary the- ory is well on its way to becoming a metatheory for all of developmental psychology. This will result in a developmental psychology that is better integrated with the life sciences as well as with dif- ferent subdisciplines within developmental psychol- ogy itself. Piaget may still be dead, but given the changes in research and theory in cognitive devel- opment over the past 2 decades, I am feeling a bit better.

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