Is Religiousness a Biocultural Adaptation? Erica Harris and Patrick McNamara In this paper, we argue that religiousness satisfies minimal criteria to be con- sidered a biocultural adaptation. Why should anyone care whether religious- ness is an adaptation? To establish religiousness as an adaptation will help to rule out some old and tiresome misconstruals of religiousness. If, for ex- ample, religiousness is an adaptation, then it is not likely to be a mere cogni- tive delusion as has been argued for centuries by anti-religious ideologues (and more recently by Dawkins 200). Adaptations evolve to solve pressing fitness-related problems. Religiousness may have evolved to solve problems that our ancestors faced, but it still may be ‘solving’ similar problems in mod- ern environments. For example, if religiousness promoted healing in some individuals in ancestral populations, it may still be doing so now. Similarly, if religiousness promoted outgroup antagonisms in ancestral populations, it may still be doing so now. Thus, evaluating potential adaptive properties of religiousness may help us to discover potential functions of religiosity. To conclude that a trait is an adaptation, we must establish specific cri- teria that any trait must satisfy in order to be considered an adaptation and then test the evidence for each of these criteria. In this paper, we lay out what we believe to be the minimal criteria any trait must satisfy to be considered a biocultural adaptation. We use ‘bio-cultural’ instead of ‘biological’ because we are discussing human beings, who are shaped by both biologic and cul- tural forces. We define religiousness as composed of two fundamental abilities: (1) the positing of belief in supernatural agents and (2) the tendency to perform rituals to relate to those agents. It is important to note that we are not ask- ing whether religiousness itself is an adaptation but whether the capacity for religiousness is an adaptation. What are the minimal criteria for a biocultural adaptation? Most evolutionary scholars would posit the following three necessary (but not sufficient) criteria for the classification of a human trait as an adapta- tion: (1) universality across cultures; (2) relative effortless-ness of acquisition of the trait (the trait is not merely learned); and (3) an associated ‘biology’, which refers to a consistent set of physiologic systems that reliably support, 80 Chapter 8 Erica Harris and Patrick McNamara mediate and produce the trait or behavior in question (Andrews, Gangestad, & Matthews 2002). A ‘biology’ of a human trait that functions as an adapta- tion would, in turn, likely include a) a genetic component as evidenced by gene-behavior correlations and heritability studies; b) a brain component as evidenced by classical neuropsychology and neuroimaging studies; and c) a chemistry component as evidenced by pharmacologic studies. The ‘specific biology’ criterion speaks to the ‘proximate mechanisms’ by which the capacity or trait in question is implemented in the real world. Details on the proximate mechanisms of an adaptive trait, in turn, can give us vital clues both as to the function of the trait and the design complexity of the trait. If the proximate mechanisms involved in support of the trait in question evidence enough complexity and enough indications of ‘design’, then details on the proximate mechanisms can help us to decide that the trait in question is indeed an adaptation as most biocultural adaptations must be complex enough and ‘designed enough’ to solve some fitness-related problem the ancestral population faced. So, in addition to the criterion of universality and of ‘effortless acquisition’, there needs to be some evidence of design; that is, the trait’s design had to solve some crucial survival-related or reproduc- tive-fitness related problem faced by our ancestors in the ancestral environ- ment. We get evidence of design from the ‘specific biology’ criterion. It is important to note that the design may not be ‘optimal’ from an engineering perspective for purposes of solving the adaptive problem it was supposed to solve, but it is sufficient. Often sexual selection drives functional traits into seemingly maladaptive or wasteful spaces (like the secondary sexual organs). Instead, by design, we mean that it can draw a reasonable link between the properties of the trait in question back to the original problem it was supposed to solve. Because the purpose of an adaptation is to solve some problem posed by the ancestral environment, in the case of human traits, that environment must include the primary ancestral social group, which has been estimated to be about 150 individuals (Aiello & Dunbar 1993). Humans evolved in an intensely social context. Biocultural adaptations, therefore, are likely to address problems of living in tightly knit social groups. We now review the evidence that religiousness satisfies the minimal criteria to be considered a biocultural adaptation. Universality The practice of religious rituals and belief in supernatural agents occurs in virtually all human cultures (Brown 1991; Murdock 195). When human universals have been carefully studied, religiousness is always found in the list of human universals, with Brown’s compendium Human Universals (1991) Is Religiousness a Biocultural Adaptation? 81 being the most recent. In addition, when Murdock chose a sample of 18 societies to represent the full-range of human experience in various types of societies, religious rituals and beliefs in supernatural agents occurred in all of them (Johnson 2005; Murdock & White 199). Effortless acquisition of religiousness Children do not need to be force-fed religiousness to posit supernatural beliefs. They do so spontaneously. Children even appear to spontaneously posit an omniscient supernatural agent. Developmental psychologists have found that children spontaneously ascribe omniscience to God—He can see all, can know all and cannot be fooled by standard theory of mind and false belief tasks (Barrett, Richert, & Driesenga 2001; Bering & Bjorklund, 2004; Kelemen 2004). Although these authors do not claim that religiouness is an adaptation, we interpret their work to be consistent with the claim that religiousness is an adaptation. Specific biology As we mentioned above, a human trait that functions as an adaptation should exhibit some evidence of design. This evidence of design boils down to evidence that the trait in question, religiousness in this case, is supported by selective biologic systems. If the biologic systems supporting the trait are dedicated to support of that trait alone and no others (a rarity in brain physi- ology), then we say that the system exhibits signs of modularity and to some extent ‘encapsulation’. It is too early to tell whether the cognitive systems sup- porting religiosity exhibit any signs of automaticity or encapsulation. They nevertheless appear to be acquired relatively effortlessly by children—even children who have received no overt instruction in religion. In these cases, the rich conceptual world concerning supernatural agents developed by the children can be contrasted to the poverty of the stimulus they are exposed to in their environment. That contrast hints at an innate contribution to devel- opment of God concepts in children. We turn now to the evidence that religiousness is associated with a spe- cific biology. Heritability Does religiousness have a genetic component? Is it heritable? This ques- tion is important as heritability implies that several sets of genes contribute to the trait in question and thus that the trait is complex and may exhibit evidence of design. Evidence that the capacity for religiousness is heritable comes from a number of classical twin studies, particularly monozygotic twins who have been reared apart. The logic in using such studies is that 82 Chapter 8 Erica Harris and Patrick McNamara these twins share the same genes but different childhood environments. For example, D’Onofrio and colleagues (1999) and Koenig and Bouchard (200) have reviewed the literature on the heritability of religiousness and found that religiousness exhibits a moderate to high heritability coefficient 2(h = 0.28-0.72; a 0.72 heritability coefficient refers to religious fundamentalists). It may even be that some people have higher doses of the relevant genes that promote this trait which in turn increases the likelihood they that will be more religious than someone with lower amounts of the gene (Hamer, 2004). These individual differences in aspects of religiousness suggest that it may, like many other heritable traits, be normally distributed in the popula- tion. Furthermore, the fact that religiousness is partially heritable suggests that it may be associated with a specific neurobiology—there should be brain systems that are consistently implicated in support of the trait religiousness. Neuropsychology and neuroimaging studies How might genes support the development of religiousness as an adaptive trait? If we have a gene, which in turn codes for a protein like the dopamine transport molecule (DAT), the genetic production of this molecule increases dopamine (DA) production. The availability of DA allows for increased released in the central nervous which has the effect of proliferating DRD4 receptors in areas of the brain that are rich in those receptors, namely the pre- frontal cortex (PFC). If the gene codes for religiousness and levels of dopa- mine are high, then a person is more apt to have higher levels of religiousness. Consequently, there should be selective areas of the brain that will be more involved in support of religiousness than other areas of the brain – namely those that have many DA receptors. The prefrontal cortex in par- ticular is densely innervated by dopaminergic efferents ascending from do- pamine synthesizing nuclei in the nigrostriatal and ventral tegmental regions of the brain. Thus, we should expect the dopaminergic prefrontal cortex to be involved in support of religious experience. Beauregard & Paquette (200) and Azari and colleagues (2001) have conducted neuro-imaging studies of brain activation patterns in religious people as they engage in religious activities.