Memes and genes evolve, and they can do so in a mutually reinforcing way. For example, let’s say a variation of the history book is published. The difference between the original version and the new one is the addition of a few more instructions at the beginning of the book, such as “Women should have as many children as possible” and “Don’t allow children to attend schools where they might be exposed to criticism of the book.” Now there are two history books in circulation. The newer book, with its additional instructions, is slightly better at replication than the old book.
