Religion is not an illness. This short discussion provides one of many arguments as to why this is the case.It is true that a lot of members of our, and most other species, suffer from cancer, but it is still not ubiquitous nor does it exist throughout the individual’s life. If a species existed, in which all, or almost all of its members suffered from the same pathology, and that pathology showed up and existed throughout the organism’s life, and this pathology has always existed within the species, that violate natural selection enough to consider the current body of theory of evolution falsified.
To be clear, it is recognized that natural selection is not the only process which occurs during evolution, but it is pretty safe to say that enough of our body of theory on evolution rests with the validity of natural selection that if natural selection were falsified, so would the body as a whole, and we would need to rework our theories.
Consider what is said in Evolutionary dynamics in structured populations.
An evolving population consists of reproducing individuals, which are information carriers. When they reproduce, they pass on information. New mutants arise if this process involves mistakes. Natural selection emerges if mutants reproduce at different rates and compete for limiting resources.
In other words, evolutionary dynamics implies natural selection. A violation of natural selection therefore would make the current theory on evolutionary dynamics less likely. Now, it could be that other processes are so powerful that they completely override natural selection, but to find a species in which natural selection has totally failed to weed out a near universal illness should present a problem for current evolutionary theory. This is how science works. If an observation is unlikely, under the assumption that a theory is true, then we consider the theory to be unlikely.
Now, it has been claim by some, including Richard Dawkins, an evolutionary biologist, that religion is a mental illness. Consider one of his tweets from 2014. I have included an archive of the tweet here, in case it is ever deleted. But in stating this notion, he argues against evolution itself, as religion is nearly ubiquitous. It exists in almost every member of the species, and has since the dawn of anatomically modern humans. It is found, in members of the population, from childhood until death. This condition would be very unlikely, if natural selection was in operation. And therefore, if we assume that Dawkins’ statement is true, we must conclude that evolutionary theory, as we view it now, is unlikely.
Interestingly, we can also define “illness” in terms of evolutionary theory: a collection of traits is an illness if it reduces the ability for that collection of trait to be passed on in future generations. This is a simplistic version, as traits interact with one another. But it is still useful. If a collection of traits increases the overall fertility and lifespan of an organism, and decreases infant mortality, it would be hard to argue that it can be an illness. When it comes to religion, the theory that religious affiliation improves fertility and life expectancy, while decreasing infant mortality, is consistent with available data, at least in the case of developing nations.
In Religion, Fertility and Genes: a Dual Inheritance Model, Robert Rowthorn addresses findings on the increase in fertility in religiously affiliated groups. Rowthorn looks at the genetic aspect of religiosity and fertility. He argues that, given multiple groups, “the genes associated with the high-fertility group may eventually predominate in the overall gene pool.” In this case, those genes are those which result in a predisposition towards religion. Overall the idea is that predisposition to religiosity and the religiosity of a group have a positive interplay on fertility, thus perpetuating the genetic predisposition and the religious group. This view is consistent with he models constructed by Rowthorn and his comparison to empirical data. (Rowthorn 2011) Meanwhile, in Religious attendance: more cost-effective than lipitor? DE Hall shows that religious affiliation seems to have a significant impact on life expectancy, with an approximate number of years gained ranging from two to three years, roughly consistent with the gain from exercise and statin related medications (Hall DE 2006). Meanwhile, according to Religious Affiliation and Under-five Mortality in Mozambique, religious affiliation, regardless of the religion, had a positive outcome on reducing under-five infant mortality. One of the potential mechanisms for this effect was theorized to be increase access to healthcare services through certain religious affiliations. Furthermore, “while the survival chances of children of Catholics/mainline Protestant and Apostolics were significantly higher than those of children of non-affiliated women, the differences among religious denominations were not statistically significant after controlling for other factors. (Boaventura M. Cau et. al. 2012)
The three studies, combined, show that findings are consistent with the view that religiosity, or at least religious affiliation, increases life expectancy and fertility, while decreasing infant mortality. The findings are inconsistent with the idea that religiosity or religious affiliation has a negative impact on these conditions. As a result, if the definition of illness mentioned above is to be accepted, then the notion that religion is an illness, of any sort, must be rejected. Furthermore, unless there was some other evolutionary mechanism that was powerful enough to override natural selection for hundreds of thousands of years, either religion is not an illness or our view of evolution must be flawed. Therefore it can be concluded, with a reasonable level of justification, that religion is not an illness.