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March 2008

God, Meet Darwin

 

Religiosity, Reproductive Advantage, and Sexual Behavior

 

How did these two adversaries end up on the same side?

 

Of the 6.5 billion humans on this planet, roughly 8% have no spiritual or religious beliefs, which poses the interesting question: what evolutionary business does this subpopulation of non-believers have with the believers? To date, the limited genetic evidence implies that the probability of inheriting your religious disposition from your parents is just about the same as inheriting your intelligence. While environmental influences weigh heavily on religious disposition, the evidence indicates that genetics, on average, is more important (see Brouchard et al. 1990).

 

But what genes? The number of genes contributing to religious (and political) disposition might number in the thousands, but given some recent evidence, those genes associated with the development and functioning of the monoamine neurotransmitter systems, in particular the dopaminergic system, seem to exert a disproportionate influence on the modulation of religiosity and political conservatism.

 

But when you talk about genetic inheritance and inter and intraspecies competition, you are talking about natural selection. This raises the question: how much has religion impacted the frequencies of certain genes, such as the dopamine D4 receptor gene (DRD4)? The impact of the so-called "adventure" DRD4 gene on human social behavior has attracted a lot of interest, as it has been connected to excessive gambling, substance abuse, elevated levels of novelty seeking, and the acceptance of spiritual transcendence. However, DRD4 studies have led to contrasting results, as the isolation of single genes to explain aggregate behaviors is a risky business.

 

But, in one of the greatest ironies in human evolutionary history, religiosity has become an active agent in the evolution of the human nervous system. In a sense, religiosity and the genes that promote it have formed a runaway selective process analogous to Fisher's runaway sexual selection. As we shall see, the religious are the most piously discerning when it comes to selecting a mate, that is, they heavily apply religious criteria towards potential mates in what we believe to be a Darwinian attempt to improve their reproductive output.

 

We suspect that the confluence of those behaviors promoted by religious doctrine combined with the genes that promote religiosity are a runaway evolutionary process. The behaviors promoted by religions tend to facilitate reproductive output, and further, provide a cultural blanket that protects the genes that promote religiosity. The most conspicuous cultural aspect of religions is morality, which we have argued to promote both reproductive output and advantage, along with behavioral inhibition of socially inappropriate reward-seeking.

 

The cultural-religious importance of morality lies in the fact that it is primarily targeted towards regulation of the behaviors associated with the dopamine system, known for its predisposition towards reward-seeking. In short, morality is a system of checks and balances for the human dopamine system. The religious do not focus on morality because they want to. They focus on it because the have to, that is, it facilitates higher reproductive output.

 

Empathy-based controls on reward-seeking are the domain of the secular liberal, and the neural substrates supporting empathy are not as dependent on the dopamine system as is morality, and are more likely to incorporate the noradrenergic system. The moral framework associated with religion provides the social controls to offset the dopaminergic nature of religious disposition. The religious do not, and can not, rely on empathy in regulating their social behavior to the extent that the secular liberals can. Indeed, religions transfer earthly reward-seeking into the afterlife, where heavenly rewards await those that inhibit their anti-social and selfish behavior on earth.

 

But the religious moral framework, combined with the dopaminergic nature of religious disposition, has led to several substantial Darwinian advantages. These are:

1. Reproductive yield
2. The survival of small breeding populations
3. Emigration to relieve population stress
4. Economic collusion
5. Welfare and income redistribution

 

All of the above advantages are interrelated. We shall briefly touch on the survival of small breeding populations and emigration, but the focus of this month's edition will be reproductive output and reproductive advantage. The evidence for elevated reproductive output by degree of religiosity is substantial. This is illustrated in the graph below.

 

2005 Population growth by percentage of non-religious
Source: World Christian Database

 

The percentage of religious in a population is highly correlated with reproductive rates. Further, reproduction is highly correlated with the degree of religiosity. So how are the religious doing it? What is the secret to their Darwinian success?

 

A, B, and C

 

Among humans, reproductive strategies are heavily integrated with social alliances, which collectively form the foundation for religious and political behavior. Due in part to the higher reproductive rates of the religious and the mounting evidence of the genetic heritability of religious disposition, natural selection has guided the human gene pool to its current religious bias.

 

In spite of the reproductive advantages of religiosity, agnosticism and atheism are still prominent tendencies, which should probably be interpreted as an evolutionary complement to religiosity. That is, a certain level of non-religiousness in a population actually improves the reproductive yield of the religious, as those with occupations in science and technology tend towards lower rates of religiosity. Humans may indeed be in an evolutionary stalemate between the genes that facilitate religiosity and reproduction, and the genes that improve technological advancement and the carrying capacity of habitats.

 

While a certain percentage of any large population is nonreligious, there is no current evidence that this percentage remains stable over time. Instability in this percentage is further promoted by environmental influences, which can rapidly modulate levels of religiosity. Further, population density and religiosity are inversely correlated variables.

 

Religious groups are a prominent fixture in the history of the colonization of new territories, and their high levels of group altruism and tight social organization provide an effective model for the survival and fertility of small populations in unfriendly habitats. In population biology, the religious most closely resemble the behavioral and reproductive characteristics of r-selected animal populations.

 

The elevation in reproductive output by the religious is executed by a diverse combination of sexual behaviors, fertility stimulants, and parenting strategies. In this light, we shall present our data in the following categories:

 

1. Desire for offspring, religious and racial tendencies in mate selection
2. Active relationships, relationship duration, numbers of different sex partners, and monogamy
3. Non-reproductive sexual behaviors
4. Male dominance, orgasmic ability, and masturbation

 

Methods and Data

 

The data represented here was collected from three separate surveys consisting of 7,488 completed question-naires administered from March 2006 through November 2007. Religious disposition in these surveys was self-rated. For correlation analysis, these religiosity cohorts were assigned a numerical religiosity variable, on a scale of 0 to 5, with atheistic = 0, agnostic = 1, spiritual = 2, little religious = 3, moderately religious = 4, and the very religious = 5.

 

All correlation coefficients are Pearson coefficients. For certain responses, which specified a range instead of a single value, we used the midpoint of that range in statistical analysis. If the top range was unbounded, (e.g. 100+ sex partners), 100 was used instead as the midpoint. This under estimates the calculation of the mean, and we have noted these statistics with an asterisk "*".

 

The data is summarized into two different schemas: religious, spiritual, and nonreligious, and, by degree of religiosity or nonreligiosity. These degrees will be atheist (AT), agnostic (AG), very religious (VR), moderately religious (MR), and a little religious (LR).

 

The religious cohort will include the very religious, moderately religious, and little religious. The nonreligious cohort will include the agnostics and atheists. The spiritual will not be aggregated into either the religious or nonreligious cohorts, although their responses are more likely to resemble the nonreligious.

 

1. Desire for Offspring, Religious and Racial Tendencies in Mate Selection

 

Mate selection is a critical element in reproductive yield, as mismatches in the number of desired children can reduce the reproductive output of the partner with the greatest desire. Since desire for offspring varies with the level of religiosity, selecting partners for religiosity has the interesting side-effect of also matching the desire for children. Indeed, this seems to be the Darwinian secret underlying the strong tendency for the religious to seek out religious partners.

Gender	Religious Disposition	N	Mean Number of Children Desired*	N	Religious Affiliation Match with Partner	N	Racial Match with Partner
Female	Religious	250	2.6	404	54.7%	340	83.2%
	Nonreligious	252	1.7	322	34.5%	264	85.6%
	Spiritual	181	2.0	212	42.0%	180	80.6%
	VR	48	3.0	135	68.2%	108	85.2%
	MR	115	2.4	172	51.7%	146	82.9%
	LR	87	2.5	97	41.2%	86	81.4%
	AG	126	1.8	238	31.9%	199	85.9%
	AT	126	1.6	84	41.7%	65	84.6%
Male	Religious	499	2.7	982	57.5%	802	84.2%
	Nonreligious	630	1.7	791	24.3%	564	80.3%
	Spiritual	206	2.2	311	32.8%	234	78.2%
	VR	134	3.5	306	64.7%	250	86.8%
	MR	226	2.5	459	58.8%	379	85.8%
	LR	139	2.1	217	44.7%	173	76.9%
	AG	226	1.9	500	24.8%	356	80.6%
	AT	404	1.6	291	23.4%	208	79.8%

Table 1: Children desired, religious and racial match with current partner
(AT=Atheist, AG=Agnostic, LR=A little religious, MR=Moderately religious, VR=Very religious) (Religious=VR+MR+LR, Nonreligious=AG+AT)

 

The number of children desired is correlated with religiosity, as evident in Table 1. The very religious (VR) in both genders had the highest mean preference for offspring, with females desiring 3.0 children, and males 3.5. These averages are about twice as high as atheists (AT), with females and males desiring 1.6 children.

 

The religious, in the process of seeking mates with common religious affiliations, are effectively seeking mates that match their desire for children and their reproductive strategies in general. This is evident from the higher correlation of partner religious affiliation with the level of religiosity (r=0.29, p<0.0001). The religious affiliation options in the questionnaire included Christian, Catholic, Mormon, Judaism, Buddhism, Hinduism, Islam, Confucianism, spiritual, agnostic, atheist, and other. If the survey respondent had a partner, we only considered it a match if the partner's religious affiliation matched the respondent's (based on the aforementioned categories). For example, it would only be considered a match if an atheist had an atheist partner, and if someone was Catholic, it would not be a match if their partner was Christian.

 

The very religious (VR) had the highest rate of matching their religious affiliation with their partners (females = 68.2%, males = 64.7%). Among males, the atheists (AT) had the lowest rate of matching religious affiliation (23.4%), while among the females; the agnostics (AG) had the lowest rate of matching (31.9%).

 

Seeking partners with the same religious affiliation is most important for those with a greater desire for offspring (i.e., the very religious), as selecting a mate with a desire for fewer children would tend to reduce the probability of achieving one's reproductive goals. Indeed, the religious were more likely to have an opinion about their partner's religion, and the nonreligious were more likely to be unsure.

 

This same phenomenon is also seen in partner racial assessments. The religious are more likely to have an opinion about their partner's race, and among the males, the religious are more likely to indicate they are of the same race as their partner. We asked the survey respondents to classify themselves into one of the following racial groups: Asian, Black, Hispanic, Indian, Middle Eastern, Native American, and White. "Not sure" was also an option in defining partner race.

 

For females, there was no correlation between religiosity and racial matching. However, for males, it was correlated (r=0.13, p<0.0001), as the very religious (VR) and moderately religious (MR) males are substantially elevated when it comes to matching the race of their partner (86.8% and 85.8% respectively). Conversely, the male atheists (AT) and agnostics (AG) were the least likely to match their partner's racial group (79.8% and 80.6%).

 

The females in this survey were more likely to have an opinion about their partner's race, and to also report they were of the same race. While the female tendency towards racial sensitivity in mate selection can be attributed to the greater female investment in reproduction, what evolutionary game are the religious males playing? Perhaps it is the same game, that is, the elevated investment in reproduction corresponds with greater sensitivity to the reproductive attributes of females.

2. Active Relationships, Relationship Duration, Numbers of Different Sex Partners, and Monogamy

 

Species with lower reproductive rates tend to neutralize their reproductive deficit by enhanced parental investment strategies. As a slowly reproducing species, humans have evolved an interesting spectrum of such strategies, and religiosity is an active component. In table 2, we see four variables with overtones in parental investment and reproductive strategies in general.

 

Religiosity and the probability of being in an active relationship are correlated variables in both genders. An active relationship in this context simply means that the person indicated they currently have a partner, although we did not identify whether this relationship was heterosexual or not. Among females, having an active partner varied with the level of religiosity.

Gender	Religious Disposition	N	Percent in an active relationship	Mean length of relationship (in years)*	Mean  different sex partners*	Self-rated Monogamy
Female	Religious	250	84.8%	8.4	10.1	9.2
	Nonreligious	252	77.4%	6.6	14.1	8.5
	Spiritual	181	75.1%	7.5	16.2	8.7
	VR	48	89.6%	10.3	5.6	9.6
	MR	115	84.4%	8.1	10.3	9.4
	LR	87	82.8%	7.6	12.4	8.6
	AG	126	79.4%	7.2	13.3	8.7
	AT	126	75.4%	6.1	14.9	8.3
Male	Religious	499	79.0%	11.1	13.3	8.8
	Nonreligious	630