Different kinds of gene cartel emerge in different gene pools. Carnivore gene pools have genes that program prey-detecting sense organs, prey-catching claws, carnassial teeth, meat-digesting enzymes and many other genes, all fine-tuned to co-operate with each other. At the same time, in herbivore gene pools, different sets of mutually compatible genes are favoured for their co-operation with each other. We are familiar with the idea that a gene is favoured for the compatibility of its phenotype with the external environment of the species: desert, woodland or whatever it is. The point I am now making is that it is also favoured for its compatibility with the other genes of its particular gene pool. A carnivore gene would not survive in a herbivore gene pool, and vice versa. In the long gene's-eye-view, the gene pool of the species — the set of genes that are shuffled and reshuffled by sexual reproduction — constitutes the genetic environment in which each gene is selected for its capacity to co-operate. Although meme pools are less regimented and structured than gene pools, we can still speak of a meme pool as an important part of the 'environment' of each meme in the memeplex.

A memeplex is a set of memes which, while not necessarily being good survivors on their own, are good survivors in the presence of other members of the memeplex. In the previous section I doubted that the details of language evolution are favoured by any kind of natural selection. I guessed that language evolution is instead governed by random drift. It is just conceivable that certain vowels or consonants carry better than others through mountainous terrain, and therefore might become characteristic of, say Swiss, Tibetan and Andean dialects, while other sounds are suitable for whispering in dense forests and are therefore characteristic of Pygmy and Amazonian languages. But the one example I cited of language being naturally selected — the theory that the Great Vowel Shift might have a functional explanation — is not of this type. Rather, it has to do with memes fitting in with mutually compatible memeplexes. One vowel shifted first, for reasons unknown — perhaps fashionable imitation of an admired or powerful individual, as is alleged to be the origin of the Spanish lisp. Never mind how the Great Vowel Shift started: according to this theory, once the first vowel had changed, other vowels had to shift in its train, to reduce ambiguity, and so on in cascade. In this second stage of the process, memes were selected against the background of already existing meme pools, building up a new memeplex of mutually compatible memes.

We are finally equipped to turn to the memetic theory of religion. Some religious ideas, like some genes, might survive because of absolute merit. These memes would survive in any meme pool, regardless of the other memes that surround them. (I must repeat the vitally important point that 'merit' in this sense means only 'ability to survive in the pool'. It carries no value judgement apart from that.) Some religious ideas survive because they are compatible with other memes that are already numerous in the meme pool — as part of a memeplex. The following is a partial list of religious memes that might plausibly have survival value in the meme pool, either because of absolute 'merit' or because of compatibility with an existing memeplex:

Organized religions are organized by people: by priests and bishops, rabbis, imams and ayatollahs. But, to reiterate the point I made with respect to Martin Luther, that doesn't mean they were conceived and designed by people. Even where religions have been exploited and manipulated to the benefit of powerful individuals, the strong possibility remains that the detailed form of each religion has been largely shaped by unconscious evolution. Not by genetic natural selection, which is too slow to account for the rapid evolution and divergence of religions. The role of genetic natural selection in the story is to provide the brain, with its predilections and biases — the hardware platform and low-level system software which form the background to memetic selection. Given this background, memetic natural selection of some kind seems to me to offer a plausible account of the detailed evolution of particular religions. In the early stages of a religion's evolution, before it becomes organized, simple memes survive by virtue of their universal appeal to human psychology. This is where the meme theory of religion and the psychological by-product theory of religion overlap. The later stages, where a religion becomes organized, elaborate and arbitrarily different from other religions, are quite well handled by the theory of memeplexes — cartels of mutually compatible memes. This doesn't rule out the additional role of deliberate manipulation by priests and others. Religions probably are, at least in part, intelligently designed, as are schools and fashions in art.

One religion that was intelligently designed, almost in its entirety, is Scientology, but I suspect that it is exceptional. Another candidate for a purely designed religion is Mormonism. Joseph Smith, its enterprisingly mendacious inventor, went to the lengths of composing a complete new holy book, the Book of Mormon, inventing from scratch a whole new bogus American history, written in bogus seventeenth-century English. Mormonism, however, has evolved since it was fabricated in the nineteenth century and has now become one of the respectable mainstream religions of America — indeed, it claims to be the fastest-growing one, and there is talk of fielding a presidential candidate.