Jesus asked, "How can I describe the Kingdom of God? What story should I use to illustrate it? It is like a tiny mustard seed. Though this is one of the smallest of seeds, it grows to become one of the largest of plants, with long branches where birds can come and find shelter." (Mark 4:30, NLT)
In this parable, Jesus seems to be reassuring his early followers that, despite their small numbers in the vast, Pagan Roman empire, God's kingdom will experience an explosion of growth, ultimately providing the umbrella under which all people can seek shelter. As we see today, his prediction of the spread of Christianity has proven correct. How has this religion achieved such dominance in the West?
Christianity, like all religions, has spread through employing effective memes. Arguably, the memeplex of Christianity has employed some of the most efficient replicators of any religion.1 Evangelism, common among many religions, is one meme employed ferociously by Christians. Christian missionaries travel the world, providing many needed functions to help the local people, and also spreading the word of God to all they help. There is no better means by which to spread your idea than by embedding in the idea itself the responsibility to witness to others.
As the number of Christians grew, another strategy meme naturally arose as a product of evangelism—repetition. The more Christians there were that were evangelizing, the more non-Christians heard the message. "[As] any advertising executive would tell you: repetition sells."2 Repetition is also prominent in the religion's rituals, as it is in most religions. Repetition of the core teachings implants the ideas more deeply into a practitioner's psyche.
Christianity employs a division of people into two categories: saved and unsaved. Believers in Christ have been saved, and non-believers can always be saved if they commit to Christ. This dichotomy utilizes three effective memes. Saved status provides the follower with both security and belonging. An eternity of separation from God is a frightful thought to people who have chosen to consider this belief structure, and committing to Christ immediately secures one from this fate. Second, it fulfills the same role as street gangs unfortunately do to many youths today; it gives the followers the feeling of belonging to something greater than themselves. Additionally, the meme of simplicity increases replication of the Christian memeplex—it is an easy process to become saved; there is no long list of steps that must be undertaken; one must simply succumb to Christ's divinity.
One final meme I'd like to discuss is the "window of opportunity" meme. Again, any salesperson will tell you that "limited time offers," "one day sales," and "store specials" increase the probability that a customer will purchase the product affected by the offer. Christianity teaches that we have a single life to live as humans, a single life in which to decide that Christ is our savior, or not. In essence, it's a limited time offer, and if we don't buy now, the offer expires.
Many more memes than the ones I've described here have all-but-ensured that Jesus's prediction would come true—Christianity has sprouted from a tiny mustard seed into a huge, wide-reaching plant. All religions that utilize fit memes have also experienced similar growth at certain times in history, including Buddhism, Islam, Judaism, and Paganism. Memes, being cultural units of transmission, are subject to changing culture and, hence, their levels of fitness will change as the cultural environment in which they spread changes. Catholicism, for instance, has experienced difficulty in recent times with its traditional views on such things as female priests. Modern culture is beginning to place greater emphasis on the reason meme, that rules should make sense, than on the tradition meme. As a result, Catholicism suffers, as one of its primary memes, tradition, becomes a poorer replicator in the primal soup of modern culture. As long as the culture is responsive to the memes employed by Christianity, it will continue to flourish as a successful religion. As the culture changes, as all cultures do, Christianity will be forced to adapt or decline.
1 The current rise of Islam raises some interesting questions as to what has changed in the culture to make Islam's memes replicate so much more effectively than in the past.
2 Brodie, Richard. Virus of the Mind. Integral Press. 1996