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When immigrants move to a new country, they bring with them the customs and belief systems of their homeland. While they may hope to pass on their traditions to their children born in this new land, their children are also inheriting the traditions and customs of the local culture.
In fact, first-generation children end up showing various psychological similarities to their local society rather than to their parents (discussed at length here, here, and here). And by the second generation are even more psychologically similar to their peers, for some traits even moving more than 50% of the way towards the values of the country to which their grandparents immigrated (as discussed in greater detail here).
The speed and ease with which first- and second-generation immigrant children assimilate to their local society and the extent to which they do shows the importance of culture and not just inherited genes from their parents in shaping their psychology. Indeed, the acculturation to local norms happens at a pace much quicker than genes could act, effectively eliminating it as an explanation for acquiring the specific contents of a local culture.
This ease of generational cultural assimilation is a highly unique capacity of human beings and a large part of the secret to our success as a species. Human beings have dispersed into virtually all ecological environments on the globe, from the tropical island of Tasmania to the freezing tundra of northern Canada, while remaining a single species. They have done so chiefly through their intellect, allowing them to enter what has been called the “cognitive niche,” along with the creation and spread of culture. These capacities have allowed people to rapidly and efficiently solve problems, flexibly change their behaviors in adaptive ways, and accumulate and transmit knowledge to successive generations. They have enabled humans to transform otherwise uninhabitable landscapes into thriving communities in which they are the dominant species.
All other organisms that have achieved ecological and behavioral diversity have done so through speciation—that is, through fragmentation into genetically distinct populations of organisms—with genomes biologically adapted to solving their environmental challenges. For instance, next to humans in terrestrial dominance is the humble and underrated ant, which has achieved enormous numbers on every continent except Antarctica. However, they have done so by speciating into over 12,000 species.
Population bottlenecks are dramatic reductions in population sizes from environmental changes. They have made humans even more genetically similar than what would otherwise be expected given the extent of human behavioral and ecological diversity. Evidence indicates that tens of thousands of years ago Homo sapiens likely went through a series of population bottlenecks, which reduced genetic diversity through the process of genetic drift.
A classic example of reduction in genetic diversity through genetic drift is what happens when a population of birds is blown off course from a continental mainland and relocates to an island in the middle of the Pacific Ocean. By various processes related to the limited ecological niches on the island and resource shortages, the founder population of birds dwindles and therefore loses genetic diversity, becoming relatively genetically homogenous.
A similar process has almost certainly happened in the evolutionary history of Homo sapiens as they migrated out of Africa and into the rest of the world. The lack of genetic variation between human populations and yet the existence of striking cultural differences, behaviors, practices, and beliefs suggests the insufficiency of genetic explanations in accounting for human behavioral variation.
All biological traits emerge through ontogenetic, also known as, developmental processes, on which selection acts. The paramount role of ontogeny or development in the evolutionary basis of human psychology has often been ignored in traditional evolutionary accounts of human behavior and along with culture have been relegated as minor players in evolutionary processes.
Ignoring ontogeny and culture in evolutionary accounts of human mind and behavior has fueled misinformation in a number of areas within human behavior. One source of misinformation has been in the proper design and methodology of studies that either strive or purport to shine light on the evolutionary basis of some aspect of human behavior.
One problem is failing to theorize about the underlying causes of human behavioral variation around the world. But more severe is the problem of ignoring cross-cultural variation in psychological characteristics in the first place, assuming some trait in a limited sample is representative of the human species (see here for a broad overview). Another one of these areas of misinformation is understanding the role of genes in behavior, including how we should interpret heritability estimates.
Why Heritability is Misleading, and Genes are Overrated
Many studies within behavioral genetics have shown that traits like intelligence (as measured by IQ tests), personality (as measured by the big five scale), and even lifetime income—and in fact, nearly all traits you can think of—are heritable and therefore at least partially shaped by genes.
However, the genetic variability that accounts for the high heritability is found within populations and not between populations. By some estimates, the vast majority of genetic variation (93-95%) is found within populations and just a tiny proportion (5-7%) is found between populations. This between-population genetic variation is likely far too small to explain documented behavioral variation in customs, practices, and languages.
A trio of researchers has recently argued that heritability is a metric that likely confuses more than enlightens. The relevant equations here are (1) the equation for variability in phenotypes and (2) the equation for heritability:
(1) Vp = Vg + Ve
(2) H2 = Vg/Vp
Heritability is nothing more than the fraction of the variability of a phenotype that can be attributed to additive genetic variation rather than environmental variation. It is a population-level metric rather than an individual-level metric and therefore says nothing about the relative amount of gene versus environmental contributions to the specific phenotypes of an individual, a common misunderstanding.
One reason why heritability estimates are so high—in other words, seemingly show high genetic contributions—within populations is because cultural and social forces like educational institutions have already done the work of homogenizing a local society, eliminating the environmental variation (Ve) in a trait about a particular mean. This then only leaves variation in genes (Vg) in the above equation (equation 1) to account for any differences in the phenotype between individuals within a population (Vp), inflating heritability estimates, and creating a misleading and overstated role of genes in human behavioral variation.
The authors refer to this as the “cultural compression problem.” This is a type of selection bias that results from the fact that there is no baseline environment against which purely genetic effects can be evaluated. All human environments have been in some degree produced and shaped by cumulative cultural evolution and a particular cultural history.
In place of purely genetic explanations some researchers have argued for a dual-inheritance approach, recognizing both the genetic and cultural inheritance of humans. Additionally, processes such as cultural group selection have been fruitful in accounting for behavioral variation across cultures. According to cultural group selection the culturally transmitted traits of different societies evolve in a Darwinian fashion similar although not identical to genes and are selected for in intergroup competition.
While cultural group selection places a strong emphasis on between-group processes, some researchers have argued for the importance of within-group processes that take into account the structure and emergent properties of cultural groups in explaining group level traits, as well as within-group processes that reflect individual-level selection and self-interest.
Overall, these cultural approaches reinforce the point that humans flexibly adopt the local culture of the society into which they are born. Since the particularities of one’s culture, including its norms and institutions, are not prespecified genetically, they therefore must be acquired culturally and ontogenetically.
Since the 1980s, cultural evolutionary researchers have documented a number of features of cultural processes and human psychology that indicate the prominent role culture has played in human mind and behavior (see here and here for instance). For example, vertical and horizontal transmission of cultural information and their differential effects on cultural variation; individual social learning and guided variation processes to acquire culture individually; and the preferential adoption of certain cultural traits over others based on their intrinsic characteristics (content biases), the characteristics of the model from whom the traits are being acquired (model-based biases), and their frequency within the population (frequency-dependent biases) (processes that are summarized concisely here and here).
Additionally, research in the evolution of human mind and behavior from a cultural perspective has shown that social and economic institutions have had significant effects on human psychology, such as the connection between economic markets and greater prosociality, fairness, and impersonal trust and the connection between paddy rice farming and greater in-group favoritism, interdependence, and holistic thinking, just to a name a few. In addition, cultural processes often create biological but non-genetic changes, for instance, the effects of literacy on brain structure.
The vast amount of evidence for the cultural and biological evolution of the human mind to create, acquire, and transmit culture shows the limitations of purely genetic explanations for behavioral variation and helps to emphasize why evolutionary accounts of human behavior must contend with culture and ontogeny.
Social Norms as a Source of Behavioral Variation
Because humans are such a cultural and cooperative species, one major factor that accounts for much behavioral variation found across cultures is social norms. Social norms are unique to the human species, owing in large part to our ability to create, sustain, acquire, and transmit culture, along with our ultra-cooperativeness. Social norms are culturally evolved rules or principles that are known by members of a group implicitly or explicitly and serve to guide and constrain behaviors. They also serve as, either directly or indirectly as a byproduct, of important markers of identification with a cultural group.
While there is an element of circularity to arguments that begin and end with social norms as explanations for behavior, there is no question that explanations of human behavioral variation will have to account for differing social norms that do exist across societies.
Social norms do not create individual mind and behavior out of a blank slate but are rooted in our evolved psychology. For example, the design of institutions being influenced by our evolved cognition, including favoritism towards genetic relatives and individual self-interest; incest taboos found across small-scale societies and the structure of social relations being influenced by our evolved predisposition of incest aversion; and customs of marriage being influenced by our evolved predisposition towards pair-bonding—a pattern of parental co-residence more common in birds than mammals (see here for a more in-depth discussion of these above examples).
However, that social norms are rooted in evolved psychological predispositions does not mean that social norms are completely reducible to the contents of our evolved psychology. One reason why is that the latter are likely far too underspecified to account for the variety of norms exhibited by different cultures. In some cultures, norms dictate that individuals ought to marry their cousins, and only their cousins on one side of the family (see here for examples in aboriginal Australian tribes). In others, norms around food sharing dictate that individuals ought to keep for themselves and their family the meat that they worked hard to hunt and obtain, whereas in other cultures, such as among Ache foragers, norms dictate that individuals ought to share the meat they obtained on their own with the broader community.
The normative domain itself originates ontogenetically in early forms of dyadic collaboration and intention sharing. Developmental and comparative psychologist Michael Tomasello argues that norms as a conceptual domain become relevant to children as early as three-years of age when they acquire the skills of collective intentionality. Collective intentionality refers to the set of skills not only to jointly attend with another to an object or event, which gives children the concept of perspective, and not only to share their intentions with one another, but also to understand conventions and express their cultural identity. Understanding cultural conventions and cultural identity is what gives children an understanding of what “we” as a cultural group do and ought to do.
The failure to carry out one’s role in a collaborative interaction, for example, playing with a toy together, provides the first source of normative force in children. At around three-years-old they begin to recognize when their collaborative partner is failing to uphold their role and will protest in a way that indicates their understanding of norms—namely, what their ineffective collaborator should, ought, or must do in order to make the collaboration work. This collaborative interaction therefore provides the first sense in which children actively engage in the normative domain, emerging from the social-cognitive processes of joint attention, shared intentionality, and collective intentionality in dyadic collaborations.
Some evolutionary behavioral researchers have downplayed the importance of cultural- and social-learning mechanisms in explaining group-level behavioral variation, instead resorting to the notion of evoked culture. This is the idea that cross-cultural behavioral variation is the result of a species-typical, individual psychology interacting with different local inputs from their environment and ecology. However, this does not explain why distinct cultures within the very same ecology can have widely differing cultural and social repertoires, an unlikely result of what an evoked cultural explanation would predict (see here for a more in-depth explanation).
Social norms are like a cultural, informational atmosphere in which individuals develop and through which they acquire standards of behavior. Social norms do not arise independently from human minds nor are they rules that give structure to a blank slate of a mind. Instead, social norms are created and enforced by, and transmitted to human minds interacting with others, often for cooperative and altruistic reasons, but also for individualistic and self-interested reasons. Understanding social norms is extremely important in understanding human behavior especially when it comes to understanding cross-cultural behavioral variation.
Differences in social norms emerge most clearly at the national level, for example, the types of foods that are eaten and the manner in which they are consumed in the U.S. versus Japan. However, differences in social norms also emerge within nations such as between ethnicities, socioeconomic classes, and at the level of families.
For example, research indicates that compared to upper class families, working class families are more likely to teach their children the values of conformity and obedience rather than creativity. This is because conformity and obedience are the kind of values that are more important and relevant to the hierarchical jobs and threat-filled environments in which working class families tend to work and live. In this way, different social norms are created, enforced, and transmitted by different subcultures within a nation, providing a large source of cultural differences that gives rise to behavioral variation.
Attending to Ontogeny in Evolutionary Accounts of Behavior
However, in addition to culture, evolutionary researchers must also recognize the importance of ontogeny, or development, in accounting for human behavioral variation. In order to fully understand any biological trait, Niko Tinbergen’s four levels of analysis must be brought to bear, namely, (1) ontogeny, (2) mechanism, (3) phylogeny, and (4) function. While these levels appear to be and often are treated as distinct and separate from one another, in reality it is important to see them as belonging together and shaping each other. It is true that ultimate levels of analysis, namely phylogeny and function have been relatively overlooked in psychology and the social sciences more generally. Nonetheless it is important to realize that proximal factors are what ultimately guide behavior under novel conditions and direct adaptive traits in relation to the present environment.
While humans come into this world with a genetic inheritance that organizes much of what becomes their psychology, it is important to keep in mind that all traits emerge through ontogenetic processes which direct genetic expression. Additionally, these ontogenetic processes continually interact with environments that then feedback on genetic expression.
Indeed, the view from modern evolutionary developmental biology (or evo-devo) is that natural selection acts not on adult endpoints, but on the ontogenetic processes that bring them into existence. Moreover, natural selection often acts in more subtle ways to shift the timing, the plasticity, or the content of an ontogenetic pathway which can have dramatic but non-genetic consequences on the form and function of phenotypes.
Great examples of these evolutionary shifts in ontogenetic pathways in terms of human behavior specifically comes from carefully controlled comparative studies between great apes like chimpanzees and bonobos and human infants (many of which are summarized here). Evidence indicates, that many human-like social-cognitive abilities are present in chimpanzees, but the chimpanzee social-cognitive abilities are often less complex, less flexible, and less elaborate. Additionally, humans possess these social-cognitive abilities far earlier in development compared to chimpanzees, providing evidence that natural selection acted on the ontogenetic timing of these processes.
One major difference in the content of the ontogenetic pathways of social-cognitive abilities between nonhuman apes and humans is that between physical and social cognition. Physical cognition refers to reasoning and problem-solving concerning space, causality, and quantities, whereas social cognition refers to reasoning and problem-solving concerning communication, social learning, and theory of mind. Nonhuman apes and humans possess similar levels of physical cognition at two-years of age. However, humans have significantly better social cognitive skills than great apes at two-years of age (see here for more recent replication and extension of the same basic finding), and are even better at four years of age, while apes stay the same.
Chimpanzees engage in cooperative activities including group hunting of monkeys; however, it has been argued that they are not truly cooperating as a group since there is no evidence that chimpanzees are representing a joint goal of catching the monkey but rather are each possessing the personal goal of wanting the monkey for themselves. In other words, chimpanzees are cognitively and motivationally individualistic and competitive rather than collectivistic in these group pursuits.
It is a similar situation to an alien scientist studying human group behavior who watches a group of humans coalesce and converge on the last new TV left in stock in the local Best Buy on Black Friday. The “groupishness” is not an indication of cooperation but rather is a byproduct of many self-interested, personally motivated individuals converging on the same thing.
In contrast, when humans work together collaboratively in groups, they are able to form a joint goal of together completing some action and having common knowledge between all agents involved that this is everyone’s intention. This slight difference in group collaboration ability between chimpanzees and humans also serves as an example of how a subtle change in a social-cognitive ability can have enormous consequences on the depth and scope of human cooperative activities.
I suspect that many of our evolved mental predispositions follow a similar process as language acquisition. When it comes to language, no child has the innate psychological specifications to learn English, Chinese, or Russian. However, every child has innate, biologically evolved, psychological specifications to acquire language. Within the solution to the general problem of acquiring a language, the specificity of acquiring the local words and rules of a particular language is offloaded to the reliably present linguistic environment that permeates every population of humans.
In contrast to the brain possessing specific and dedicated mental mechanisms for complex behaviors, I believe that much of the work of acquiring and executing complex behaviors is likely offloaded to the reliably occurring social-cognitive environments populations of humans create. These environments are then subsequently encountered by newborns and acquired throughout their prolonged maturational timeframe.
While being species-typical, the contents of these social-cognitive environments and how they interact with individuals differ across societies. The differences in the social-cognitive environments individuals encounter through development constitute major influences on their psychology and the particular beliefs, practices, and behaviors they exhibit. Michael Tomasello, has a similar and much more detailed argument regarding these ontogenetic processes that he built over decades of research and has summarized most comprehensively here.
Research in genetics and evo-devo has shown that the gene-to-phenotype connection is far looser than what was typically thought among non-human animals. This is even truer in humans for whom ontogenetic and cultural processes play a major role in creating and shaping psychology. Therefore, no evolutionary explanation of human behavior is complete without recourse to culture and ontogeny, which together account for a large portion of human behavioral variation.
While striving to understand human universals is a worthy goal and of great importance within the evolutionary sciences, it also can run the risk of overlooking cross-cultural behavioral variation and the factors that give rise to it, an explanation for which is key to understanding universals. Explicitly attempting to understand behavioral variation (for a great recent example of this see here) helps to put culture under the microscope. This will ultimately help to make sense of both the evolved mechanisms that give rise to it and the relationships between behavioral variation, ontogeny, culture, evolved mechanisms, and socioecological factors, which together form the complex tapestry of human psychology.