Twin Studies and the Role of Genetics in Religious Belief
Adult twins provide insights into how genetics may sway religious paths.
Posted February 12, 2026 | Reviewed by Margaret Foley
I recently studied a 12-year-old identical male twin pair, Jim and Carl. Interestingly, their mother revealed that her twins were being raised in different religions, i.e., her husband's and her own. (Her husband is Jewish, and she is Lutheran.) The couple agreed that if the twins were to choose the same religion when they are older, that would be fine with them.
This is an unusual situation for several reasons: (1) It creates differences between the brothers from an early age. Each twin would be exposed to different religious beliefs and practices, and (2) each twin would become part of a different community, leading to different individual friendships. It is interesting to speculate as to how the twins’ outcomes might evolve. Let's first consider twin studies of religiosity , namely interests and involvement in religion.
Early studies of young twins raised together did not find genetic effects on religiosity. However, young twins are under the guidance of their parents, so identical and fraternal pairs did not differ in religious resemblance. This is evident in a study of 850 high-school twins that found little difference in the degree of resemblance between these two types of twins in their involvement in religious affairs. In contrast, later twin studies recruited older twins, including adult twins reared apart from birth. Reared-apart twins completed five different scales with items relating to religious leisure time, occupational interests, activities, leisure time interests, and values. A comparison group of reared-together twins completed the leisure time and occupational interest scales. The identical reared-apart pairs showed greater resemblance than the fraternal reared-apart pair across the two scales they completed in common. It, therefore, appears that when twins become adults, they are no longer following their parents’ wishes and are free to choose the religious activities and interests they like.
An example of identical reared-apart identical twins who hold similar religious values, despite being raised by different families and in different religions, is illuminating. In particular, this case shows that tendencies toward religion have a genetic effect even when twins have different families, although the content of their religiosity (Jewish and Christian) differs. This example is followed by religious divergence in identical male twins who grew up together.
Identical twins Sharon and Debbie were separated at birth and reunited at age 45. They met at the Hartford, Connecticut, airport, not far from Debbie’s residence; Sharon flew in from Kentucky. Debbie had been raised in a Jewish home, while Sharon had been raised in a Christian home. Both twins were deeply religious, unlike the unrelated siblings with whom they were raised.
Identical twins Miklos and Gyorgy were born in 1913 in Hungary to a Jewish couple. However, the twins were raised in the Catholic faith because of Jewish persecution following World War I—many Jewish families did this for both acceptance and acculturation. When the twins were attending university, Miklos considered joining a Christian group, but remained aware of his Jewish roots. He also felt that Gyorgy was abandoning his Catholicism. Then Gyorgy gained a certain insight and joined the priesthood, surviving World War II in Italy. In contrast and despite his Catholicism, Miklos was taken by officers to Bergen-Belsen, a concentration camp in Germany, where he understood, acknowledged, and reclaimed his Jewish roots. In fact, he celebrated Jewish holidays with fellow prisoners. The twins remained apart for many years, reuniting in 1956, when both moved to America. Their meeting did not go well—they stayed estranged from one another even though they lived only a few miles apart. Unfortunately, Miklos and Gyorgy could not see past their differences, even though they had been very close as children and as young adults. Perhaps the reason is that Gyorgy made a conscious decision to surrender his Jewish roots, while his twin brother suffered horribly in the camp; had Gyorgy remained in Hungary, he would have experienced the same fate as his twin.
Loehlin, J.C., & Nichols, R.C. (1976). Heredity, environment, and personality: A study of 850 sets of twins. Austin, TX: University of Texas Press.
Pogany, E.L. (2000). In my brother’s image: Twin brothers separated by faith after the Holocaust. NY: Viking.
Segal, N.L. (2012). Born together-reared apart: The landmark Minnesota twin study. Cambridge, MA: Harvard University Press.
Share this post Facebook Bluesky Linkedin Email
There was a problem adding your email address. Please try again.
By submitting your information you agree to the Psychology Today Terms & Conditions and Privacy Policy
Nancy L. Segal, Ph.D. , is a professor of psychology and the Director of the Twin Studies Center, at California State University, Fullerton.
Get the help you need from a therapist near you–a FREE service from Psychology Today.
This article is part of the Bringwise Psychology Journal — daily insights on human behavior, mental health, and personal growth.