evolutionary biologists and philosophers will be in hiding from the then-dominant religious groups. Fifty years from now, no one stubbing his or her toe will say, “Charles Darwin, Charles H. Darwin, this hurts!” but they will still be saying, “Jesus H. Christ, this fucking hurts.”
At the same time, many, many people believe religion is the received truth from the Almighty—or, more to the point, that their religion is. Some have a book—a Torah, a Bible, a Koran—all of whose words are true, often literally so. Their view has as little backing as the viral-meme story and appears at first to be nothing more than a deep form of self-justification. If their own religion is God’s own truth, then competing religions are often seen as anti-truth, or the work of the devil, the ultimate target. So we begin with two very extreme views of religion, with the truth probably somewhere in between, but where exactly and why?
First we need to separate the truth value of religious statements from the possible benefits of believing in them, and likewise separate partaking in religious ceremonies from the truth value attributed to them. Then we need to analyze beliefs and behavior in a more fine-grained way so that we can evaluate the meaning and function of particular beliefs. In my own view, there is often an internal struggle within religions between general truth and personal or group falsehood. That is, the essence of religion is neither self-deception nor deep truth, but a mixture of the two, with self-deception often overwhelming truth.
Religions tend to increase within-religion cooperation at the cost of lowered cooperation with outsiders. Often this involves a false historical narrative and shared group self-deception: “We are the chosen people or the original people from creation or those whose beliefs [e.g., in the divinity of Jesus] cause God to favor us [or whatever].” In short, religions often act as templates for in-group/out-group biases. Insofar as they encourage in-group cooperation, many benefits may accrue, but insofar as they encourage in-group cooperation in aggressive attacks on out-groups, they both inflict harm on others as a price of their cooperation and inflict harm on self when they fail (which, in warfare, is roughly half the time).
At the same time, certain features of religion provide a recipe for self-deception, removing nearly all restraints from rational thought. The universal system of truth espoused by a religion usually gives special status to the believer. Various phantasmagorical things are easily imagined, and “faith” is permitted to supersede reason.
Religion has a complex relationship with health and disease. On the one hand, health may be a major selective factor favoring religious behavior and beliefs. Not only do religions often preach healthy behavior, but there also is evidence that religious belief and association improve individual survival, immune function, and health. Even music, so common in religion and courtship, has positive immune effects. Medicine was originally embedded within religion, and both provide strong placebo benefits to at least part of the population.
A completely unexpected association between disease and religion emerges when we study the entire globe for degree of religious diversity (number of religions per unit area) as a function of parasite load (roughly, degree of human loss due to parasites). Here we find many more religions (and languages) per square inch when parasites are high. Since splitting of religions is also naturally associated with ethnocentrism and ethnic differentiation, parasites are a factor expected to degrade general religious truth value over time and thus to be positively associated with in-group deceit and self-deception. This may be especially true of the polytheistic religions, but with monotheism came additional forces of self-deception associated with global conquest and a single, dominant spirit.
Finally, we consider the role of prayer and meditation, specific teachings against self-deception, and the contrast between the social and internal sides of religious devotion.
COOPERATION WITHIN THE GROUP
By logic, religion ought to increase altruistic and cooperative behavior among group members—of obvious potential benefit—but it may do so along with reduced such behavior toward nonmembers and, worse still, outright aggression and murder. That is, an increased degree of hostility toward neighboring groups can heighten the within-group bias (and vice versa). This is the double-edged sword of religion, inside and outside: a religion urges its own members to treat each neighbor as they would treat themselves, yet also to slaughter every nonbeliever and outsider, as is ordered in the good book, for group after group, down to every last man, woman, and child. At the extremes, some religions advocate in-group