Natural selection can be defined as non-random differential reproduction of randomly varying organisms. Professor Richard Dawkins argues that any system wtih randomly varying replicators whose triats can be passed down from one generation to next generation will undergo Darwinian evolution. Richard Dawkins in his book "The Selfish Gene" introduced the concept of memes.

A meme can be defined as any idea or behaviour that can pass from one person to another by learning or imitation. It is a unit of cultural information that can be transmitted from one mind to another mind via verbally or by repeated action. A song, article, idea or any other cultural traits like wearing cap, dresscode are memes. When memes spread from one mind to another mind they might not be copied exactly and hence they undergo mutation. Memes are subject to variation, mutation and inheritance and hence they undergo Darwinian evolution. Human culture is envirionment for memes.

Religion can be thought of as collection of memes. Religious books contains ideas which are handed down from generation to generation. Religion are subject to evolution by natural selection, in this case working on memes. We can see from example of Christianity. Chrisitianity was initially just one religion but today it has evolved into many denominations just like spieces evolves into several different spieces over the course of time. Some religions tend to spread more than others because they have "memes of evangilism and proselytizing". Religious memes compete with each other for believer's mind space and time. Any religious meme which can exploit believer's mind with maximum efficiency would tend to spread more in "human culutral pool of ideas". Religions like spieces can go extinct for several reasons like being over run by newly evovled memes. Ancient Egyptian and Norse religions became extinct when they were over run by newly evolved religions like Christianity and Islam.