CDPXXX10.1177/0963721420917736HeyesPsychological Mechanisms Forged by research-article9177362020

ASSOCIATION FOR PSYCHOLOGICAL SCIENCE

Current Directions in Psychological Science Psychological Mechanisms Forged 2020, Vol. 29(4) 399­–404 © The Author(s) 2020 Article reuse guidelines: by Cultural Evolution sagepub.com/journals-permissions DOI:https://doi.org/10.1177/0963721420917736 10.1177/0963721420917736 www.psychologicalscience.org/CDPS

Cecilia Heyes All Souls College and Department of Experimental ,

Abstract The adaptive features of cognitive mechanisms, the features that make them fit for purpose, have traditionally been explained by nature and nurture. In the last decade, evidence has emerged that distinctively human cognitive mechanisms are also, and predominantly, shaped by culture. Like physical technology, human cognitive mechanisms are inherited via social interaction and made fit for purpose by culture evolution. This article surveys evidence from developmental psychology, comparative psychology, and cognitive neuroscience indicating that imitation, mentalizing, and language are “cognitive gadgets” shaped predominantly by cultural evolution. This evidence does not imply that the minds of newborn babies are blank slates. Rather, it implies that genetic evolution has made subtle changes to the human mind, allowing us to construct cognitive gadgets in the course of childhood through cultural learning.

Keywords cognitive gadgets, cultural evolution, cultural learning, evolution of cognition,

What makes psychological mechanisms well suited for evidence, reviewed in this article, suggests that many their designated roles (i.e., fit for purpose)? Why is it distinctively human cognitive mechanisms, including that visual systems can see, learning mechanisms can imitation, mentalizing (or “theory of mind”), and lan- learn, and reasoning processes can reason? They are guage, have been shaped by a cultural selection process all complex products of nature and nurture, but who analogous to genetic evolution. In this cultural evolution- or what designs the features that enable cognitive pro- ary process, variants arise in individual development, cesses to do their jobs? rather than by genetic mutation, and are culturally In many cases, genetic evolution (nature) leads the learned; they are inherited via social interaction rather design team. The neonatal face bias—the tendency of than DNA. “Good” variants are culturally learned by newborn babies to orient to faces (Johnson, 2005)—has more agents, but this need not be because the teachers been honed by natural selection over biological genera- or the learners understand what makes them “good” tions. Variant systems were genetically inherited, and (Heyes, 2018). through differential reproduction, those that were better at promoting early attention to faces proliferated, Cultural Evolution of Cognitive Mechanisms whereas the others died out. Learning (nurture) plays a relatively minor role in the development of the neo- It has long been recognized that behavior and technol- natal face bias, but in other cases, it is the dominant ogy, rather than cognitive mechanisms, can be made fit force. For example, the development of configural face for purpose by cultural evolution (Boyd & Richerson, processing—the capacity to recognize faces as wholes 1985). Cultural selection has produced the multistage rather than using distinctive features—is relatively behavioral process—involving scraping, grating, wash- unconstrained by genetically inherited information and ing, and boiling—used by people in West Africa to instead depends on experience of a large number of faces (Le Grand, Mondloch, Maurer, & Brent, 2004). For some distinctively human cognitive mechanisms— Corresponding Author: absent in other animals or present there only in nascent Cecilia Heyes, University of Oxford, All Souls College and Department form—cultural evolution (culture) is a third member of of Experimental Psychology, Oxford OX1 4AL, United Kingdom the design team, alongside nature and nurture. Recent E-mail: [email protected] 400 Heyes

learn from other people. In cultural learning, what the learner learns depends on what the model or teacher knows. When cognitive gadgets are culturally learned, input from the sender enables the receiver’s cognitive system to reconstruct the mental software that gener- ated the sender’s modeling or teaching behavior. Thus, the information that builds a cognitive gadget from old parts (i.e., psychological processes shared with other animals) comes from other people who have already acquired the mechanism. It is inherited like money rather than like eye color, through cultural learning rather than DNA (Heyes, 2019).

Fig. 1. Cognitive gadgets. Like simple pieces of tangible technology, Imitation such as canoes, distinctively human cognitive mechanisms can be made fit for purpose by cultural evolution. These cognitive gadgets We are “Homo imitans” (Meltzoff, 1988), better able are constructed in the course of childhood development through than any other species to copy the topography of body social interaction. movements—the way in which parts of the body move relative to one another. We use our prodigious capacity remove cyanide from cassava, making it safe and nutri- for imitation to acquire the facial expressions, bodily tious to eat (Henrich, 2015). Similarly, the design of gestures, and ritualistic movements (e.g., dance and canoes has been shaped by cultural selection. When sports) that promote cooperation with members of our people wanted to make a new canoe, they copied the own social group and act as shibboleths, setting us design of an old one. The old canoes available for apart from other groups. copying were the ones that had not sunk or fallen Since the 1970s, it has been widely believed that apart—the canoes that were relatively good at doing imitation is a cognitive instinct made possible by a their jobs. Therefore, without needing to understand powerful, genetically inherited mechanism that relates why some canoes are better than others, people copied the “felt but unseen movements of the self with the good canoes more often than less-good canoes, and seen but unfelt movements of the other” (Meltzoff & the design of these simple boats improved incremen- Moore, 1997, p. 179). In the last 20 years, this consensus tally as a result (Rogers & Ehrlich, 2008). has broken down for two reasons. First, the cognitive- Now it is becoming clear that not just tangible tech- instinct theory of imitation was based on experiments nology, such as canoes, but also mental technology, suggesting that human newborns can imitate a range of cognitive mechanisms, can be shaped by cultural selec- facial expressions, but subsequent studies have failed tion (see Fig. 1). Some distinctively human psychologi- to replicate these experiments. For example, Oostenbroek cal mechanisms are not “cognitive instincts” (Pinker, et al. (2016) conducted a study of more than 100 neo- 1994), shaped primarily by genetic evolution, but “cog- nates using the cross-target procedure introduced by nitive gadgets,” made fit for purpose primarily by cul- Meltzoff and Moore (1977), which measures the fre- tural evolution (Heyes, 2018). quency with which infants produce a gesture after As we will see in the case studies that follow, evi- observing the same gesture and alternative gestures. dence that a cognitive mechanism is a gadget rather This study failed to find evidence of imitation of any than an instinct typically comes from research on its of the nine gestures tested. Second, evidence is mount- development—from studies showing that a way of pro- ing that the capacity to imitate depends on a vocabulary cessing information is acquired from other people of learned sensorimotor associations (Catmur & Heyes, through social interaction. The development of cogni- 2019; Catmur, Walsh, & Heyes, 2009). Each of these tive instincts is guided by genetically inherited, domain- associations links a visual image of an action with a specific information (e.g., innate grammar) and noncultural representation of how it feels to perform the action. forms of learning (known as “individual learning” and They are forged by self-observation—for example, “social learning”). In contrast, the development of cog- when babies watch their own hands in motion—and, nitive gadgets depends on genetically inherited, domain- crucially, through social interactions in which children general information (e.g., enabling sensory, motor, and engage in synchronous activities (e.g., playing pat-a-cake) all-purpose learning capacities) and on a specific kind or are imitated by adults. Evidence supporting this cogni- of social learning: cultural learning. Children are not tive gadget, or “associative-sequence-learning” model of merely influenced by their social environments; they imitation, comes from behavioral and neurophysiological Psychological Mechanisms Forged by Cultural Evolution 401

others. In cognitive science, behavior is typically explained with reference to neural or computational mechanisms, but in everyday life, people in many contemporary cul- 0.6 tures explain, predict, and justify behavior by appealing 0.5 to what agents think and want. “She shoved the old man 0.4 Eyebrow because she thought he was going to be hit by a car.” “She 0.3 Mouth raised her hand because she wanted to bid for the paint- 0.2 ing.” As these examples illustrate, mentalizing underwrites our moral and legal obligations, and it is associated with 0.1 prosocial behavior in childhood (Imuta, Henry, Slaughter, 0.0 Mimicry Score Selcuk, & Ruffman, 2016). −0.1 Increasingly, the development of mentalizing looks −0.2 like the development of print reading or literacy, a skill that we know is not “in our genes” because scripts have −0.3 High Low been around for only 5,000 to 6,000 years—not enough Maternal Imitation time for us to have evolved a reading instinct (Heyes & Frith, 2014). For example, parents and other adults Fig. 2. Maternal imitation promotes the development of infant imita- tion. The graph shows 4-month-olds’ mean mimicry score (activation scaffold the development of print reading by exposing over the corresponding muscle region minus activation over the non- children to easy to read words, such as “cat,” before corresponding muscle region) based on electromyographic record- hard to read words, such as “yacht.” Similarly, when ings of their mouth and eyebrow muscles, separately for infants who talking to their infants, mothers mention easy to read are imitated frequently by their mothers (high group) and infants who are imitated less often (low group). The asterisk above the bracket mental states, such as desires and emotions, before hard indicates a significant difference between groups, and the symbols to read mental states, such as beliefs and knowledge, above the data bars indicate marginally significant and significant and the frequency of developmentally appropriate refer- † differences from zero ( p < .10, *p < .05). Error bars indicate +1 SEM. ences to mental states predicts the children’s later devel- Figure adapted from de Klerk, Lamy-Yang, and Southgate (2019). opment of mentalizing skill (Taumoepeau & Ruffman, 2008). Instruction is also important in the development experiments showing that, even in adults, the propen- of both print reading and mentalizing. Just as children sity to imitate is highly plastic. A brief period of incon- are instructed in rules of pronunciation (e.g., told what gruent sensorimotor experience, in which participants “-tion” sounds like when read aloud), in conversation observe one action while performing another, is suf- with their children, mothers make “causal-explanatory” ficient to block or reverse an automatic tendency to statements that specify relationships among situations, imitate the trained movements (Catmur et al., 2009). behavior, and mental states (e.g., “He is smiling because Convergent evidence comes from naturalistic studies of he is happy. He is happy because he is playing with the mother–infant interaction. In a longitudinal study in puppy”), and the frequency of these causal-explanatory which spontaneous interactions within mother–infant statements predicts individual differences and cultural dyads were observed monthly at home from 1 to 10 variation in the development of mentalizing (Slaughter months, Markodimitraki and Kalpidou (2019) found that & Peterson, 2012). the frequency with which infants initiated imitation of These findings, and many others (e.g., Pyers & sounds and body movements was correlated with that Senghas, 2009), suggest that people learn to mentalize of their mothers. Mothers who initiate more imitative through social interaction with members of their social interactions have infants who do the same, and the group who are already skilled mentalizers. In principle, effect is action specific. Maternal imitation of facial this cultural learning could be guided by a genetically movements, recorded during spontaneous interaction, inherited cognitive instinct for mentalizing. However, is positively correlated with infant imitation of face but parallels with print reading cast doubt on what used to not hand movements, suggesting that mother–infant be regarded as evidence for the innateness of mental- interaction supports imitation by enabling infants to izing. For example, print reading also shows neural learn action-specific sensorimotor associations (Fig. 2; specialization—it depends heavily on certain parts of de Klerk, Lamy-Yang, & Southgate, 2019). the brain—indicating that cognitive gadgets are just as likely as cognitive instincts to be specialized at the Mentalizing neural level. Similarly, print reading, like mentalizing, is subject to developmental disorders. People with dys- Mentalizing (also known as theory of mind and mind lexia have difficulty with print reading, and people with reading; Wellman, 2018) occurs when we ascribe mental autism spectrum disorder have difficulty with mental- states, such as beliefs and desires, to ourselves and to izing (Heyes & Frith, 2014). 402 Heyes

Experiments using looking-time measures suggest processes without built-in language-specific constraints. that young infants are capable of mentalizing when For example, computers can learn grammatical rules they have had relatively little opportunity for cultural without any preprogrammed grammatical knowledge learning (Onishi & Baillargeon, 2005). However, the (Christiansen & MacDonald, 2009). Experiments exam- results of these studies are proving difficult to replicate ining individual differences in typically developing (Baillargeon, Buttelmann, & Southgate, 2018; Dörrenberg, adults and children indicate that they use the same Rakoczy, & Liszkowski, 2018; Poulin-Dubois et al., sequence-learning processes to learn artificial and “real” 2018), and even if the looking-time effects are reliable, linguistic grammars (Kidd & Arciuli, 2016). Research they can be explained by domain-general mechanisms, with nonhuman animals has confirmed that domain- such as attention and working memory, that is, without general sequence-learning capacity has increased in the assuming that human infants are born with a propensity hominin lineage and provided a plausible model of to mentalize. Domain-general mechanisms cobble how this change has been implemented in the primate together cognitive gadgets using input from cultural brain (Bornkessel-Schlesewsky, Schlesewsky, Small, & learning. However, many human capacities, including Rauschecker, 2015). behavior prediction in infancy, depend on “neat” domain- Most interesting from an historical perspective, general mechanisms, not on the domain-specific, distinc- research now indicates that infants and children are tively human cognitive gadgets built by those mechanisms frequently corrected by adults when they make gram- (Heyes, 2014). matical errors and that these social signals are used in language learning (Taumoepeau, 2016). This evidence challenges Chomsky’s “poverty-of-the-stimulus” argu- Language ment (Chomsky, 1975) for the innateness of language Even language, the foundational cognitive instinct and, like research on sequence learning, confirms novel (Pinker, 1994), is beginning to look like a cognitive gad- predictions of the hypothesis that language has been get, shaped predominantly by cultural rather than genetic made fit for purpose primarily by cultural evolution. evolution (Christiansen, Chater, & Culicover, 2016). Start- ing in the 1990s, evolutionary psychologists cited Implications research on developmental disorders, neural specializa- tion, and the genetic bases of language in support of The evidence that imitation, mentalizing, and language Chomsky’s proposal that the development of language are cognitive gadgets does not imply that the mind of is grounded in innate knowledge of grammatical rules. a newborn human baby is a blank slate. In common However, much of this evidence has now been over- with other animals, humans genetically inherit not only turned. For example, specific-language impairment, a perceptual and motivational processes but also a wide developmental disorder once thought to affect language range of domain-general cognitive mechanisms. They acquisition alone, turns out not to be specific to lan- are domain general in that they process information of guage. Children diagnosed with the condition struggle different kinds—for example, about other agents and to learn sequences of lights and objects, not just the about the inanimate world—using the same set of com- order of words (Hsu & Bishop, 2014). Similarly, there putations. They mediate selective attention, memory, does not appear to be a language center in the brain. learning, and executive functions, such as response Broca’s area in the left hemisphere has long been inhibition and task switching. Most of these domain- regarded as the seat of language, but recent research general processes are widely distributed across the ani- suggests that language is scattered throughout the cor- mal kingdom and are found in birds and small mammals tex. Meta-analysis of brain-imaging studies shows that as well as primates. However, there is evidence that, in Broca’s area is in fact more likely to be active when the human lineage, they have been tweaked by genetic people are performing tasks that do not involve lan- evolution in ways that allow us to absorb information guage than when they are reading, listening to, and from other agents quickly and easily. producing words (Poldrack, 2006). Furthermore, the For example, humans genetically inherit a face bias, forkhead box protein P2 (FOXP2) gene, once regarded a tendency to look longer at faces than at other stimuli, as a language gene, has been implicated in sequence which locks our attention on other agents from birth learning more generally. Transgenic mice implanted (Johnson, 2005). Similarly, adult humans are friendlier— with the human version of FOXP2 are better than their more tolerant of social contact and more strongly moti- siblings at finding their way around a maze (Schreiweis vated by social rewards—than adults of many other et al., 2014). primate species (Cieri, Churchill, Franciscus, Tan, & Alongside these developments, there is positive evi- Hare, 2014), which gives children the opportunity to dence that language can be acquired, by computers learn from a host of other agents, not only their mothers. and by children, via domain-general sequence-learning Furthermore, compared with other animals, including Psychological Mechanisms Forged by Cultural Evolution 403 nonhuman primates, humans have expanded capacities (See References). A rigorous, large-scale study that did not for learning and memory, allowing us to absorb the find any evidence of imitation in human newborns. information supplied by other agents in large volumes and at unprecedented speed (Heyes, 2018). Humans Transparency genetically inherit psychological features that are only Acting Editor: Robert L. Goldstone subtly different from those of other animals, but they Editor: Robert L. Goldstone allow us to upload from our cultural environment not Declaration of Conflicting Interests only a wealth of knowledge and technical skills but The author(s) declared that there were no conflicts of also new pieces of mental technology—cognitive interest with respect to the authorship or the publication gadgets. of this article. I have focused on imitation, mentalizing, and lan- guage because, to date, these processes have been ORCID iD examined most closely from a cultural evolutionary Cecilia Heyes https://orcid.org/0000-0001-9119-9913 perspective. 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