For the past 500 years, to varying degrees, the processes of religious secularization have been occurring in what today are the wealthy, highly educated, industrialized nations of the world. They are causing organized religion, as a social institution, to go from being a very important influence on the lives of people and the nations in which they live to being a smaller influence, or almost no influence at all. Various disciplines from theology to psychology to sociology have tried to explain secularization, each discipline contributing something unique. One discipline that has not contributed has been biology. From a biological perspective, based on observation and reasoning, at least one of the ultimate functions of the physical forms associated with religion appear to be that of in-group marker for a breeding population, which, as will be shown, is how all religions start. Religions structure larger human populations into smaller “clusters” that are separate in-group breeding populations. The clustering into smaller in-group breeding populations prevents the spread of contagious diseases and creates inter-group competition and intra-group cooperation, both of which have contributed to human eusociality, a very rare type of social organization that will be explained. As the physical forms of religion are losing this in-group-marker function of clustering populations with modernity, a general biological principle comes into play, which is “form follows function, and as function wanes, so does form.” When applied to religion, “form” means the physical components by which all religions are built. The specific meaning of “physical,” as used here, will be explained in the article. This biological perspective, which is counter-intuitive and can generate testable hypotheses, should complement, not compete, with perspectives from other disciplines. Physical forms in biology can and often do have more than one function, so the same form with a biological function can also have psychological and theological functions. The physical forms of religion are its objects of natural (genetic and cultural) selection. As socio-economic modernity spreads through the world, the evolutionary biological trajectory suggests that religion, as a social institution, will eventually become extinct.
