I am frequently asked by journalists to recall the most surprising finding of our twin studies. The study of religion and belief in God is the one that always comes to mind, and the results are not easily accepted by many people. Most people can accept diseases or height and even weight being genetically heritable to some extent, but when it comes to our personal beliefs we tend to be more skeptical. For many, the idea that there is a genetic component to our faith -- or lack of it -- is a stretch too far and damages the concept of self-determination that we hold so dear.We have laws against discriminating against various immutable inborn characteristics, and laws against religious discrimination, but no one wants to believe that religion is inborn. After all, people freely join or leave religions all the time.
Nevertheless science has shown us clearly that one level of belief in God and overall spirituality is shaped not only by a mix of family environment and upbringing -- which is not surprising -- but also by our genes. Twin studies conducted around the world in the U.S., the Netherlands and Australia as well as ours in the U.K. show a 40 to 50 percent genetic component to belief in God. ...
Skeptics among you might say that the twin studies showing similarity for belief are just reflecting some cultural or family influence that wasn't properly corrected for in the study design. However in one study of adopted twins, the researchers looked at religious belief in a number of adopted twins raised apart. They found exactly the same result -- greater similarity in identical twin pairs, even if raised apart. The conclusion is unavoidable: faith is definitely influenced by genes.
I am referring to Christianity and similar religions here. For Christians, religious belief is accepted as voluntary. Islam and Judaism have the concept that if you are born into the religion, then you can never leave.