Seymour Kety's Danish adoption study found genetic evidence for schizophrenia by comparing adopted individuals with schizophrenia to both their biological and adoptive relatives, showing that schizophrenia correlates with biological rather than adoptive family membership, demonstrating that genetics alone transmit the trait.

In heterozygotic inheritance (like sickle cell trait providing malaria resistance), schizotypy genes are maintained in populations because the mild version provides adaptiveness through cultural roles like shamanism, while the homozygotic version (full-blown schizophrenia) is costly; thus there has been selection for schizotypy genes, not schizophrenia genes.

In contemporary American polls, 25% of Americans believe in ghosts, 36% believe in mental telepathy, 47% believe in alien visitation and UFOs, and more than half believe the devil is a literal being rather than a metaphor, indicating that Western culture has not eliminated irrational magical thinking but rather celebrates it in different forms.

Obsessive-Compulsive Disorder (OCD) is an anxiety disorder characterized by obsessions (intrusive thoughts that won't stop) and compulsions (repetitive actions the person feels compelled to perform), and the most common OCD compulsions across all cultures are: (1) washing/cleansing rituals; (2) food safety and purity rituals; (3) ritualistic behaviors when entering/leaving significant places; and (4) numerology and magical number compulsions.

Psychiatrist Judith Rapoport described OCD using the metaphor of a fixed action pattern—like a dog circling its blanket before sleep—where the person with OCD is the dog that can never stop circling; they can only temporarily hold off the anxiety and dread, which inevitably returns.

Hinduism's Brahminical tradition includes six hours of daily handwashing and body washing rituals, specific rules about which foot to place outside first in the morning, rules about which direction to face while on the toilet, ritualistic breathing ratios involving nostril-blocking, and the magical number 24, which structurally parallels OCD cleansing and numerological compulsions.

Religious ritual gives sanctuary and sanction to individuals whose lives might otherwise be completely taken over and destroyed by obsessive-compulsive drives, by providing a shared social framework that names, legitimizes, and structures the compulsions as devotion rather than pathology.

Martin Luther, a 16th-century Augustinian monk, exhibited severe OCD symptoms throughout his monastic life: taking vows of silence for extended periods, repeating prayers obsessively, extending his first mass to four hours due to perceived errors in pronunciation or sincerity, and confessing intrusive thoughts about God's anger—behaviors his mentor recognized as pathological (saying 'For some reason, you are angry at God').

Religious traditions celebrate self-mutilation and self-flagellation as proof of devotion—believers beat themselves bloody, whip themselves, pierce their fingers and cheeks—which is psychiatrically suspect as a sign of psychosis in non-religious contexts but is sanctioned and celebrated in religious ones.

Holy anorexia (anorexia mirabilis) was common during the 13th-15th centuries among nuns who fasted to the point of death to prove their love of God, framing starvation as devotion; one nun consumed only leper scabs and pus for the final month of her life, claiming it was the most delicious nectar she had ever eaten.

Religion depends on a constant tension between cognitive rationality and intuitive faith, where faith is defined as belief in what cannot be proven and cannot be disproven; religion loses its power if the things one is supposed to have faith in are actually proven, as Jesus indicates by refusing to jump off the temple to prove his divinity to Satan.

In B.F. Skinner's experiments with hungry pigeons, random food delivery created superstitious conditioning: pigeons attributed agency to their own random behaviors (standing a certain way, dabbing) and believed they caused the food, eventually ritualistically performing these irrelevant behaviors—demonstrating that pattern-finding and false causality attribution occur when uncertainty and need are high.

Damaging the hippocampus in lab rats lowers the threshold for superstitious conditioning, making it easier to condition false causality beliefs—suggesting a neural substrate for susceptibility to magical thinking and religion.

Religious evolution shows a progression from comprehensible anthropomorphic gods (like Greek gods with human desires) to unknowable, hidden gods (invented by Judaism) who lack familiar appetites and cannot be understood, requiring individuals to project their own needs onto the blank canvas of the unknowable deity.

Individuals on the autism spectrum are religious at similar rates as neurotypical individuals, but differ in what they attribute to God: neurotypical individuals attribute moral qualities to God (judgment, love), while autistic individuals attribute God to inanimate physical processes (magnetism, gravity, keeping electrons in their orbitals).

Damage to the dorsolateral prefrontal cortex (measured in war veterans with head injuries from bullets or shards) is associated with higher rates of mystical experiences and increased reliance on intuition over rational cognition.

Religiosity is not genetically determined; rather, it emerges as an emergent property of having 80 billion neurons with all their complexity, similar to how aesthetics, philosophy, and economic views emerge; there is zero evidence for a gene or handful of genes for religiosity.

The Scandinavian example demonstrates that religiosity is largely environmentally determined: Scandinavian countries were highly religiously observant in the mid-19th century, but as socialist social safety net models developed, religiosity declined to the lowest rates in Europe within a century—a timeframe too short for genetic change, showing social context determines religiosity more than genes.

Desert-dwelling populations developed monotheistic religions with punishing afterlives and gods who actively monitor and judge human behavior, while rainforest-dwelling polytheistic religions have different structures; these ecological patterns reflect different survival pressures and livelihood strategies (pastoralism vs. farming vs. hunting).

Across European history, religiosity correlates with poverty, violence from feudal lords, and infectious disease burden—the more hardship and disease, the higher the religiosity; this pattern continues worldwide.