A cultural species: How culture drove human evolution

Joseph Henrich holds the Canada Research Chair in Culture, Cognition and Coevolution at the University of British Columbia, where he is appointed in both the psychology and economics departments. His theoretical work focuses on how natural selection has shaped human learning and how this in turn influences cultural evolution, and culture-gene coevolution. Methodologically, his research synthesizes experimental and analytical tools drawn from behavioral economics and psychology with in-depth quantitative ethnography, and he has performed long-term fieldwork in the Peruvian Amazon, rural Chile, and Fiji. Trained in anthropology, Dr. Henrich’s work has been published in journals in biology, psychology, anthropology and economics. He is the co-author (with Natalie Henrich) of Why Humans Cooperate (2007). In 2004, while he was on the faculty at Emory University, he was awarded the U.S. Presidential Early Career Award. In 2009, the Human Behavior and Evolution Society awarded him its Early Career Award for Distinguished Scientific Contributions. Dr. Henrich is currently a fellow of the Canadian Institute for Advanced Research. Author website.

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Long before the origins of agriculture, humans expanded across the globe, from the arid deserts of Australia to the frozen tundra of the Canadian Arctic. Surviving in this immense diversity of habitats depended not on specific genetic adaptations, but on large bodies of culturally transmitted know-how, abilities, and skills that no single individual could figure out in his or her lifetime (e.g., blowguns, animal tracking). Lacking local cultural knowledge, many an explorer has perished in supposedly “harsh” environments in which local adolescents would have easily survived (Boyd, Richerson, & Henrich, 2011a). Even among foraging societies, humans show an immense variety of social organizations, group sizes, kinship structures, and mating patterns: more diversity than the rest of the primate order combined (Henrich & McElreath, 2007). Ethnographically, this diversity is at least partially rooted in culturally-acquired and widely shared social rules. No other species depends on cultural information to this degree, and paleo-anthropological evidence increasingly suggests that culture appears early in the evolutionary history of our genus (Alperson-Afil et al., 2009; Brown et al., 2009). Overall, much theory and evidence now converges to indicate that we are an ultra-cultural species —unlike any other—whose brains, genes, and biology have long been shaped by the interaction between cultural and genetic evolution. Culture appears to have opened up entirely new evolutionary vistas not available to less cultural species.

Taking these observations seriously, my colleagues and I have focused on constructing an evolutionary account of human behavior and psychology that fully incorporates culture and cultural evolution under the Darwinian umbrella. Rather than directly applying existing theoretical insights from evolutionary biology to humans, our approach develops from first principles a new class of evolutionary insights (Laland, Kumm, & Feldman, 1995). Often using formal evolutionary models (Boyd & Richerson, 1985), we consider how evolutionary processes might shape a species so heavily dependent on learning from others. Moreover, while rooted in evolutionary thinking, this approach draws tools and methods from diverse disciplines (Mesoudi, 2011), including anthropology (Henrich & Henrich, 2010), genetics (Laland, Odling-Smee, & Myles, 2010; Richerson, Boyd, & Henrich, 2010), archaeology (Henrich, 2004b; Shennan, 2001), psychology (Mesoudi, 2009b),  and economics (Henrich, 2000; Henrich et al., 2001). In particular, much empirical work focuses on systematic, comparative, long-term field work in diverse human communities—including small-scale societies—using a combination of ethnographic, observational, and experimental methods (Henrich et al., 2004; Henrich & McElreath, 2002; Henrich & Henrich, 2007). This framework interconnects and organizes several disparate research programs within psychology with ongoing efforts across the social sciences.

This approach, termed Dual Inheritance or Gene-Culture Coevolutionary Theory (Boyd & Richerson, 1985; Laland, et al., 1995), can be organized around three key concepts (Henrich & McElreath, 2007):

1. Cultural capacities as adaptations: Culture, cultural transmission, and cultural evolution arise from genetically evolved psychological adaptations for acquiring ideas, beliefs, values, practices, mental models, and strategies from other individuals by observation and inference. Thus, the first step in theorizing is to use the logic of natural selection to develop hypotheses about the evolution and operation of our cultural learning capacities (Rendell et al., 2011). 

2. Cultural evolution: These cognitive adaptations give rise to a robust second system of inheritance (cultural evolution) that operates by different transmission rules than genetic inheritance, and can thus produce phenomena not observed in other less cultural species. Theorizing about these processes requires taking what we know about human cultural learning and cognition, embedding them into evolutionary models that include social interaction, and studying their emergent properties with the goal of making empirical predictions. 

3. Culture-gene coevolution: The second system of inheritance created by cultural evolution can alter both the social and physical environments faced by evolving genes, leading to a process termed culture-gene coevolution. For example, it appears that the practice of cooking spread by social learning in ancestral human populations. Once spread, ‘cooked food’ became a selective force that shrunk our digestive tracks, teeth, stomachs, and gape (Wrangham, 2009). Such a reduced investment in digestive tissues may have freed up energy for more brain building, and perhaps a greater reliance on cultural information. Empirical evidence from genetics suggests that culture has long shaped our genome (Laland, et al., 2010; Richerson, et al., 2010).

Cultural Capacities as Cognitive Adaptations

Approaching our capacities for learning as adaptations to more effectively extract adaptive information from the world around us (Boyd & Richerson, 1985; Henrich & Boyd, 1998) provides a rich set of evolutionary hypotheses (Chudek & Henrich, 2010; Rendell et al., 2010; Rendell, et al., 2011). For example: my colleagues and I have theorized that both children and adults should use cues of skill, success, experience, age, sex, ethnic markers and received deference (“prestige”) to preferentially direct their attention toward some people (“models”) over others for the purposes of learning (Henrich & Gil-White, 2001; Henrich & McElreath, 2003). This approach unites otherwise disparate lines of research, from psychology, economics and other disciplines. Within psychology, empirical support can be found in the work of Bandura and colleagues (Bandura, 1977; Rosenthal & Zimmerman, 1978), as well as in many separate research programs within social psychology such as those focused on conformity, persuasion, and influence (Mesoudi, 2009b). Recent work in developmental psychology, for example, has shown that infants and young children preferentially attend to and learn from those individuals exhibiting (1) greater skill or success (Birch, Vauthier, & Bloom, 2008; Brosseau-Liard & Birch, in press; Corriveau & Harris, 2009), (2) cues of confidence (Birch, Akmal, & Frampton, 2010), (3) more experience, including using age as an indirect cue (Jaswal & Neely, 2006; Stenberg, 2009), and (4) ethnic markers (Shutts, Kinzler, Mckee, & Spelke, 2009). These laboratory findings dovetail with field work in small communities that examines how people aggregate different cues to select their preferred models (Henrich & Broesch, 2011).

Our developmental team tested the evolutionary hypothesis that young children would use the attention and preferential gaze of others as a cue to direct their own cultural learning efforts. We exposed 3-5 year olds to two models (people they could learn from) who were being differentially watched by others in an initial cuing scene. Then, when they were alone, each model made different choices, including operating an artifact in different ways and selecting from among different foods and drinks. While showing no conscious awareness of the differential attention or play preferences for the models, the children preferentially imitated the artifact manipulation and food and drink choices of the models that were watched more by other people in the initial scene (Chudek, Heller, Birch, & Henrich, 2011).

Many of the formal evolutionary models underpinning such predictions, while developed with humans in mind, should be applicable to non-humans. Experimental work among species ranging from rats to sticklebacks (fish) has recently demonstrated that, while no cumulative cultural evolution occurs in non-humans, these species do use many of the same adaptive cues and biases predicted by the theory (Galef, 2009; Hoppitt & Laland, 2008). This is important because it demonstrates the broad applicability of this approach.

The importance of such a framework is not merely that it generates non-intuitive predictions, such as the use of “prestige cues,” but that it unifies otherwise disconnected lines of research, both within psychology and across diverse disciplines (including biology), into a single theoretical framework. The most persuasive work on the use of success cues, for example, comes from experiments in economics (Henrich & Henrich, 2007: reviewed in Chapter 2) while the most rigorous experimental work on the importance of conformity effects in cultural learning comes from experimental anthropology (Efferson, Lalive, Richerson, McElreath, & Lubell, 2008; McElreath et al., 2008). Field evidence for the effects of these learning biases outside the laboratory comes from arenas as diverse as the diffusion of innovations literature (Henrich, 2001; Rogers, 1995) and the cultural transmission of suicide from sociology (Henrich & Henrich, 2007: reviewed in Chapter 2; Mesoudi, 2009a; Rubinstein, 1983; Stack, 1987).

Recognizing the centrality of culture in human life leads to a novel evolutionary theory of status and status psychology (Henrich & Gil-White, 2001). Evolutionary researchers have tended to assume that human status is merely an extension of primate dominance hierarchies. However, because humans are so heavily dependent on an information economy for survival, our species has evolved a second avenue to social status that operates alongside dominance and has its own suite of cognitive and affective processes. The theory predicts that these two types of status, labeled dominance and prestige, can be distinguished by their ethological displays, patterns of imitation and deference, memory biases, and affective responses. Recent empirical work by our status team, in both the laboratory and field, has revealed the expected patterns for prestige vs. dominance, and has shown that both forms of status can coexist and influence group decision-making and attention (Cheng, Tracy, Foulsham, & Kingstone, 2011; Cheng, Tracy, & Henrich, 2010; Foulsham, Cheng, Tracy, Henrich, & Kingstone, 2010).

This work connects with the emotion literature where prior empirical studies had indicated the existence of two facets for the emotion pride—labeled authentic and hubristic pride (Tracy, 2007). Our ongoing efforts suggest that hubristic pride is associated with dominance-status and authentic pride with prestige-status (Cheng, et al., 2010). This lays a principled theoretical foundation and explanation under an otherwise purely empirical program. In the process, it integrates emotion work into a much broader set of theoretical interconnections that include work on cultural learning, imitation, persuasion, leadership, attention, and aggression (Cheng, et al., 2011).

The existing work on status within psychology is bedeviled by a lack of theoretical clarity. Much empirical work treats status as a uni-dimensional construct, and then unknowingly operationalizes it as either prestige or dominance, or some mix of the two. This may explain the confusing and contradictory results that plague this literature. Meanwhile, through brute empiricism, other researchers continually re-discover aspects of the two dimensions (prestige and dominance), often without realizing just how many times this has occurred (Henrich & Gil-White, 2001). Labels like power, dominance, status, expertise, collaborative leadership, and coercive leadership are applied differently depending on the literature and sub-discipline. The hope is that ground-up evolutionary theorizing regarding status might help unify these efforts into a single set of cumulative research programs. At this point, our approach has generated some follow-up by other researchers, including work that hormonally distinguishes prestige and dominance (Johnson, Burk, & Kirkpatrick, 2007), reveals related emotions (Algoe, Haidt, & Silvers, 2006), demonstrates strategic female mate preferences (Snyder, Kirkpatrick, & Barrett, 2008), applies our concept to celebrity gossip (De Backer, Nelissen, Vyncke, Braeckman, & McAndrew, 2007) and explores the impact on economic decision-making (Bruno, 2006; Eckel & Wilson, 2000). Work in small-scale human societies indicates that both forms of status lead to higher fitness, albeit via different mechanisms (von Rueden, Gurven, & Kaplan, 2011).

Cultural Evolution and Culture-Gene Coevolution

Once a species is sufficiently reliant on learning from others for at least some aspects of its behavioral repertoire, cultural evolutionary processes can arise, and these processes can alter the environment faced by natural selection acting on genes. To develop models of cultural evolution, we begin by taking the theoretically-grounded and empirically-tested hypotheses about our learning psychology—who people learn from and what they tend to infer while learning—to construct models that examine what happens when lots of individuals are learning in these ways, and interacting over generations. Because of their fidelity and frequency of use, human cultural learning abilities are probably unique in giving rise to cumulative cultural evolution, the process through which learning accumulates successful modifications and lucky errors over generations. Cumulative cultural evolution builds complex adaptive practices, tools, techniques, and bodies of knowledge (e.g., about animal behavior and edible plants) that continue to improve over centuries and millennia (Boyd & Richerson, 1996; Boyd, et al., 2011a; Henrich, 2004b).

Models of cumulative cultural evolution suggest two important, and perhaps non-intuitive, features of our species. First, our ecological success, technology, and adaptation to diverse environments is not due to our intelligence. Alone and stripped of our culture, we are hopeless as a species. Cumulative cultural evolution has delivered both our fancy technologies as well as the subtle and unconscious ways that humans have adapted their behavior and thinking to tackle environmental challenges (Henrich & Henrich, 2010). The smartest among us could not in a single lifetime devise even a small fraction of the techniques and technologies that allow any foraging society to survive (Boyd, et al., 2011a; Henrich, 2008). Second, the available formal models make clear that the effectiveness of this cumulative cultural evolutionary process depends crucially on the size and interconnectedness of our populations and social networks. It’s the ability to freely exchange information that sparks and accelerates adaptive cultural evolution, and creates innovation. At the population level, it is much better to be social than it is to be smart. Such approaches help us understand archaeological and ethnographic cases in which isolated populations gradually lose their most complex technologies. Sustaining complex technologies depends on maintaining a large and well-interconnected population of minds (Henrich, 2004b, 2006, 2009b; Powell, Shennan, & Thomas, 2009). 

These cultural evolutionary models also help us to understand how our cognitive processes for cultural learning give rise to many sociological phenomena, like social classes, castes (Henrich & Boyd, 2008), cultures of honor (McElreath, 2003), ethnic groups (Boyd & Richerson, 1987; Henrich & Henrich, 2007: Chapter 9; McElreath, Boyd, & Richerson, 2003) and large-scale cooperation (Boyd, Richerson, & Henrich, 2011b; Henrich, 2004a). In the case of ethnic groups, for example, such models explore how genes and culture coevolve. This shows how cultural evolution will, under a wide range of conditions, create a landscape in which different social groups tend to share both similar behavioral expectations and similar arbitrary “ethnic markers” (like dialect or language). In the wake of this culturally constructed world, genes evolve to create minds that are inclined to preferentially interact with and imitate those who share their markers. This guarantees that individuals most effectively coordinate with those who share their culturally learned behavioral expectations (say about marriage or child rearing). These purely theoretical predictions were subsequently confirmed by experiments with both children (Kinzler, Dupoux, & Spelke, 2007; Kinzler, Shutts, Dejesus, & Spelke, 2009; Shutts, et al., 2009) and adults (Efferson, Lalive, & Fehr, 2008).  

This approach also suggests that cultural evolution readily gives rise to social norms, as long as learners can culturally acquire the standards by which they judge others (Chudek & Henrich, 2010). Many models robustly demonstrate that cultural evolution can sustain almost any behavior or preference that is common in a population (including cooperation), if it is not too costly (e.g., Boyd & Richerson, 1992; Henrich, 2009a; Henrich & Boyd, 2001). This suggests that different groups will end up with different norms and begin to compete with each other. Competition among groups with different norms will favor those particular norms that lead to success in intergroup competition (Boyd & Richerson, 2002; Boyd, et al., 2011b; Henrich, 2004a). My collaborators and I have argued that cultural group selection has shaped the cultural practices, institutions, beliefs and psychologies that are common in the world today, including those associated with anonymous markets (Henrich et al., 2005; Henrich et al., 2010), prosocial religions with big moralizing gods (Atran & Henrich, 2010; Shariff, Norenzayan, & Henrich, 2010), and monogamous marriage (Henrich, Boyd, & Richerson, forthcoming). Each of these cultural packages, which have emerged relatively recently in human history, impacts our psychology and behavior. Priming “markets” and “God” (Shariff & Norenzayan, 2007), for example, increase trust and giving (respectively) in behavioral experiments, though “God primes” only work on theists. Such research avenues hold the promise of explaining, rather than merely documenting, the patterns of psychological variation observed across human populations (Henrich, Heine, & Norenzayan, 2010)

The cultural evolution of norms over tens or hundreds of thousands of years, and their shaping by cultural group selection, may have driven genetic evolution to create a suite of cognitive adaptations we call norm psychology (Chudek & Henrich, 2010; Chudek, Zhao, & Henrich, forthcoming). This aspect of our evolved psychology emerged and coevolved in response to cultural evolution’s production of norms. This suite facilitates, among other things, our identification and learning of social norms, our expectation of sanctions for norm violations, and our ability to internalize normative behavior as motivations.

The coevolved norms psychology hypothesized by these models unites much work from across the social sciences. It proposes that learners should act as though they live in a world governed by social rules they need to acquire, many of which are prosocial. Young children show motivations to conform in front of peers (Haun & Tomasello, in press), spontaneously infer the existence of social rules in one trial learning, react negatively to deviations by others to a rule learned in one trial, spontaneously sanction norm violators (Rakoczy, Warneken, & Tomasello, 2008) and selectively learn norms (that they later enforce) in the predicted ways (Rakoczy, Hamann, Warneken, & Tomasello, 2010; Rakoczy, Warneken, & Tomasello, 2009).

This approach also predicts that humans ought to be inclined to “over-imitate” for two different evolutionary reasons, one informational and the other normative (Henrich & Henrich, 2007). The informational view hypothesizes that people over-imitate because of an evolved reliance on cultural learning to adaptively acquire complex and cognitively-opaque skills, techniques and practices that have been honed, often in nuanced and subtle ways, over generations. In support of this view, children and adults from diverse societies accurately imitate adults’ seemingly unnecessary behaviors (they ‘over-imitate’) even though they are capable of disregarding them (Lyons, Young, & Keil, 2007; Nielsen & Tomaselli, 2010). However, because individuals should also “over-imitate” because human societies have long been full of arbitrary norms (behaviors) for which the “correct” performance is crucial to one’s reputation (e.g., rituals, etiquette), we expect future investigations to reveal two different kinds of over-imitation. This lays a theoretical foundation for research on natural pedagogy by suggesting that humans are programmed to attend to cues that activate an expectation of learning normative information (Topal, Gergely, Miklosi, Erdohegyi, & Csibra, 2008). 

The selection pressures created by reputational damage and punishment for norm-violation may also favour norm-internalization. Neuroeconomic studies suggest that social norms are in fact internalized as intrinsic motivations in people’s brains. Both cooperating and punishing in locally normative ways activates the brain’s rewards or reward anticipation circuits in the same manner as does obtaining a direct cash payment (de Quervain et al., 2004; Fehr & Camerer, 2007; Tabibnia, Satpute, & Lieberman, 2008).

A broad range of recent findings can be explained by recognizing that experimental games tap culture-specific norms, often involving monetary transactions with strangers. First, measures of fairness and willingness to punish from standard bargaining experiments vary dramatically across societies in a manner that covaries with market integration and community size, respectively (Chudek, et al., forthcoming; Henrich, Ensminger, et al., 2010). Second, framing the games to cue local norms can alter behavior in predictable ways (Henrich, et al., 2005; Herrmann, Thoni, & Gächter, 2008), including findings showing that the same frames have different effects in different populations (Goerg & Walkowitz, 2010; Pillutla & Chen, 1999; Poppe, 2005; Ross & Ward, 1996). Third, game behaviors can be experimentally influenced by observational learning (Cason & Mui, 1998), and prosocial behavior emerges gradually over development (unlike reciprocity), not plateauing until people reach their mid-twenties (Sutter & Kocher, 2007). Finally, non-human primates—who lack norms or coevolution—fail to reveal the prosocial preferences toward strangers so puzzling in the largest-scale human societies (Jensen, Call, & Tomasello, 2007; Jensen, Hare, Call, & Tomasello, 2006; Silk et al., 2005).

The thrust of this line of research is that cultural evolution was likely a dominant force driving our species’ genetic evolution over the last few hundred thousand years. Through its autocatalytic processes (Chudek & Henrich, 2010), ever accumulating cultural elements may have driven our brain expansion, cognitive specializations (Herrmann, Call, Hernandez-Lloreda, Hare, & Tomasello, 2007), social psychology (Henrich & Henrich, 2007) and physiological changes in our guts, teeth, hands and bones (Wrangham, 2009). Understanding and theorizing how cultural processes have shaped human evolution provides a framework that unifies and underpins research programs across the social, biological, and historical sciences.

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