Responding to your question, “I’d like to know why they would share religion. Is this because they are adopted through religiously-affiliated adoption agencies??” I was not thinking so much about religiously-affiliated adoption agencies as I was about countries and cultures with a dominant religion. For example, it is likely that birthparents and their adopted-away offspring in Spain grow up with the teachings of the Catholic religion, which influences people’s beliefs and behaviors. This is an example of a major non-genetic behavioral influence shared by birthparents and adoptees. They may not have grown up together in the same family, but they grew up and live together in similar non-familial social environments. Another example would be adoptions made within religious communities such as the Pennsylvania Amish, where we would expect to see much behavioral resemblance for non-genetic reasons.