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									     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.

     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.

    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 (h2 =
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. Beauregard & Paquette studied
15 Carmelite nuns and asked them to recall the most intense mystical experi-
ence of their lives and imaged their brains using fMRI. Azari and colleagues
imaged the brains of six religious subjects who recited the first verse of
Psalm 23 using PET. Both studies found overlap of activated brain regions
on the right-side of the forebrain, including the prefrontal cortex and cor-
responding activation in the left-side subcortical sites. These areas contain
the highest number of DA receptors, particularly in the right dorsolateral
Is Religiousness a Biocultural Adaptation?                                   83

and orbito-frontal cortices. The most striking result of these neuro-imaging
studies is that the right-side of the PFC is consistently activated during in-
tentional and private religious practices. As mentioned above, the prefrontal
lobes are densely innervated by dopaminergic fibers ascending from the sub-
stantia nigra (SN) and the ventral tegmental area (VTA) in the brainstem.
If the prefrontal lobes are especially implicated in the mediation of religious
experiences, then religiousness should be influenced by pharmacologically-
induced changes in dopaminergic activity.

     Drugs that enhance DA transmission can induce religious experiences
in persons who are well-disposed to religiousness or spirituality. Drugs that
block DA transmission can reduce religiously-tinted delusions in various
psychiatric populations (Nichols & Chemel 200). It is important to note
that drugs that influence other transmitters, like acetylcholine, do not have
as strong an effect on religiousness as do drugs that influence DA.
     To further support the hypothesis that religiousness has a specific bi-
ology that is especially influenced by dopaminergic systems, we can look at
patterns of religiousness in patient populations that exhibit dramatic altera-
tions in dopaminergic functioning such as Parkinson’s disease (PD). Levels
of dopamine are 40% below normal in these patients (Agid, Javoy-Agid, &
Ruberg 1987). McNamara and colleagues (200) recently reported that
these patients do in fact report lower levels of religiousness than their age-
matched counterparts.
     If dopamine is in fact functionally implicated in the mediation of reli-
giousness, then genes that code for construction of proteins that construct
the dopamine molecule should be associated with scores on religiousness
scales, and that is in fact what we find. The DRD4 gene in the brain was
found to correlate positively with different religious tests; higher levels of
this gene were linked to higher levels of religiousness (Comings, Gonzales,
Saucier, Johnson, & MacMurray 2000).
     To sum up, we find that 1) religiousness is associated with moderate to
high heritabilities; 2) there are genes that are correlated with religiousness;
3) these genes code for neurotransmitters that promote DA activity in spe-
cific regions of the brain that are high in DA receptors; 4) the PFC is high
in DA receptors; 5) different neuroimaging techniques have demonstrated
high (relative to baseline condition) activation levels in the right PFC during
religious activity; and ) religiousness varies in patient populations accord-
ing to levels of dopaminergic activity in the brains of these patients. All of
these data suggest that religiousness is supported by a fairly specific biologic
84                                   Chapter 8 Erica Harris and Patrick McNamara

system and that it exhibits a fair degree of biocultural complexity. In short,
the proximate mechanisms that support the trait religiousness likely involve
right-sided prefrontal dopaminergic activity. This biology of religiousness
in turn supports the claim that religiousness exhibits design complexity and
therefore could be adaptive.
     If religiousness is an adaptation, what problem did religiousness solve
for our ancestors? Evolutionary scholars have offered several possibilities,
such as health promoting effects and facilitating cooperation. Although ad-
ditional research is currently being done to evaluate these possibilities, we
feel that more research into the biology of religiousness is necessary.
     Claims about the potential adaptive functions of religiousness need to
be treated with great caution and tested against the evidence that it is not an
exaptation or a spandrel. From the evidence presented, religiousness is a trait
that is universal in all cultures, is effortlessly acquired, and has a specific biol-
ogy which includes genetic heritability, activation of brain structures, and a
drug-modulating effect. There is also evidence of design that supports the
trait. However, do our findings concerning a specific biology help us decide
between the adaptive possibilities of religiousness? We know that activation
of the pre-frontal dopaminergic cortex is associated with placebo respond-
ing and social cooperation tasks. But, work in this area is still in its infancy.
The evidence as it currently stands, while intriguing, does not yet help to
constrain existing hypotheses on the adaptive function of religiousness.

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