  We address the problem of diversification in religions by studying selection
on cultural memes that colonize humans hosts. In analogy to studying the
evolution of pathogens or symbionts colonizing animal hosts, we use models for
host-pathogen dynamics known from theoretical epidemiology. In these models,
religious memes colonize individual humans. Rates of transmission of memes
between humans, i.e., transmission of cultural content, and rates of loss of
memes (loss of faith) are determined by the phenotype of the cultural memes,
and by interactions between hosts carrying different memes. In particular,
based on the notion that religion can lead to oppression of lower classes once
a religious society has reached a certain size, we assume that the rate of loss
increases as the number of humans colonized by a particular meme phenotype
increases. This generates frequency-dependent selection on cultural memes, and
we use evolutionary theory to show that this frequency dependence can generate
the emergence of coexisting clusters of different meme types. The different
clusters correspond to different religions, and hence our model describes the
emergence of distinct descendent religions from single ancestral religions.
