The Field of Evolutionary Neuroscience: A Commentary on “Rethinking Norm Psychology” by Cecilia Heyes

There are two dominant themes in Heyes’s article. First, she proposed a “cognitive gadget” hypotheses for how the psychology of norms is constructed. In opposition to gene-based theories of a domain-specific innate norm psychology, she made a case that norm psychology is built during development by the domain-general processes of culture acquisition and associative learning. Second, she sets the debate within a “poverty/wealth scheme” designed to make these hypotheses testable. This terminology stems from “poverty of the stimulus” arguments used to support gene-based theories of syntax. Allegedly, children are not exposed to enough information in the language they hear to infer syntactic rules. Hence, syntax must be innate.

We think that both themes are important contributions. Our remarks are directed at the methodological issue of how hypotheses formulated on evolutionary and cognitive grounds can actually be tested. We argue that mechanics of the constraints and trade-offs needed to implement the poverty/wealth scheme are substantially the province of neurobiology. What is needed to formulate cogent cognitive hypotheses and test them is a science of evolutionary neuroscience.

The evolutionary side of such a field characterizes the adaptive problems that living in a particular environment imposes on organisms living in it. Boyd and Richerson (1985) attempted such an evolutionary functional analysis of culture and found that culture might function to solve adaptive problems in highly variable but moderately autocorrelated environments. It subsequently turned out that Pleistocene has been characterized by just such environments. This hypothesis suggests that human behavior must be highly flexible but also generally genetic fitness enhancing (Boyd et al., 2011). However, these conclusions rested on shaky guesstimates of things such as the relative metabolic costs and error rates of individual and social learning. We also worry about a “poverty of the genes” problem. The number of genes, including regulatory genes, is fairly large but far smaller than the astronomical number of synapses in the brain. As Edelman (1985) noted, it is hard to imagine how genes can wire the brain in great detail, and there is no sign in developmental neurobiology that it does so. General evolutionary and macro functional considerations do provide some constraints on possible proximal designs but only rather loose ones.

This is a general problem in understanding evolutionary design. In terms of anatomy, physiology, and other proximal features of complex adaptations, there are generally many designs that are at least locally optimal (Boyd & Richerson, 1992; Gavrilets, 2004). Historically independent solutions to problems such as vision or flight are typically distinctively different and are governed by different constraints and trade-offs (Goldsmith, 1990). Thus, to understand in any detail how and why human brains are designed the way they are requires the collaboration of top-down evolutionary functionalism (What is the adaptive problem or problems the human mind/brain designed to solve?) and bottom-up neurobiology (How can primate nerve cells and circuits be organized to solve these problems?; Williams et al., 2021). Other “brainy” creatures, such as octopuses, have solved analogous problems with rather different neural architectures (Hochner, 2012).

Consider how neurobiology can contribute to the understanding of human brains in the case of Heyes’s proposal about the large role of associative learning in the construction of norms. Jaak Panksepp (2004) developed an account of vertebrate emotional circuitry using detailed maps of the highly conserved subcortical emotional circuits. Because of the relative simplicity of these circuits, this can be done in mammalian model organisms such as rats. The results can be extrapolated to humans because, for example, drugs such as cocaine stimulate particular emotions and cause similar behavior in people and the mammalian models. Some of these circuits, such as play, are experienced as pleasurable, and others, such as fear, are experienced as aversive. Together with the appetitive emotions such as hunger and thirst, the emotions provide the reinforcement and inhibition necessary for associative learning. The emotional circuits project into the neocortex and receive projections from the neocortex, as would be required if associative learning and social learning were part of a sophisticated phenotypic adaptation system as Heyes proposed. Given this architecture, we can make testable neurological-level hypotheses accounting for the unique features of the human cognition and behavior. For example, humans’ highly social nature hypothetically derives from the up-regulation of affiliative emotions, such as care, play, and panic, that support mainly mother–infant bonding in typical mammals but also the much more promiscuous human bonding with mates, kin, and friends, even symbolically marked groups as in patriotism. Culture-specific patterns of norm-controlled behavior, such as the Southern Culture of Honor (Nisbett & Cohen, 1996), are probably based on the developmental up-regulation of the emotions anger and fear. Human neurobiology seems to have coevolved with people’s cultural niche adaptation on the multigeneration timescale and codeveloped via learning and cultural transmission on the generational timescale. The molecular basis for human-specific social adaptations is beginning to be understood (Duerler et al., 2022).

A number of neurobiological research programs support Heyes’s gadget picture, interpreted as neocortical circuitry. Anderson’s (2014) meta-analysis of functional MRI data supports the idea of cognitive capacities developing through neuronal recycling. Small bits of neocortical tissue take on distinctive micro-functions that are organized developmentally into functional cognitive circuits and can be redeployed for novel functions, such as reading and counting. A program in cultural neuroscience seeks to understand the neurobiological basis of cultural differences in behavior (Kitayama et al., 2019). Neuroeconomics investigates neurobiological explanations for the choice behavior so important to economics (Williams et al., 2021). The neurobiology of cortical development is an active field (Libé-Philippot & Vanderhaeghen, 2021). Neurobiology of cognitive flexibility is tolerably well understood (Dajani & Uddin, 2015). Neurosurgical work highlights the flexibility of neocortical circuitry (Herbet & Duffau, 2020). We do not think that work to date rules out competing hypotheses such as Carey and Spelke’s (1994) core cognition proposal that envisions some role for specialized human-specific cognitive circuits such as those involved in people’s capacity for social learning.

The neurobiological roots of cultural diversity and cultural adaptation are already well established by evolutionary neuroscience.

For a longer version, see Richerson and Boyd (2022). For a model of norm internalization, see Gavrilets and Richerson (2017).