If the Martians can’t make any of these theories fit the facts, they should consider a default theory of sorts that we may call the pearl theory: religion is simply a beautiful by-product. It is created by a genetically controlled mechanism or family of mechanisms that are meant (by Mother Nature, by evolution) to respond to irritations or intrusions of one sort or another. These mechanisms were designed by evolution for certain purposes, but then, one day, along comes something novel, or a novel convergence of different factors, something never before encountered and of course never foreseen by evolution, that happens to trigger the activities that generate this amazing artifact. According to pearl theories, religion isn’t for anything, from the point of view of biology; it doesn’t benefit any gene, or individual, or group, or cultural symbiont. But once it exists, it can be an objet trouvé, something that just happens to captivate us human agents, who have an indefinitely expandable capacity for delighting in novelties and curiosities. A pearl begins with a meaningless speck of foreign matter (or, more likely, a parasite), and once the oyster has added layer after beautiful layer, it can become something of coincidental value to members of a species who just happen to prize such things, whether or not this coveting is wise from the point of view of biological fitness. There are other standards of value that may emerge, for reasons good or bad, free-floating or highly articulated. In much the way the oyster responds to the initial irritant and then incessantly responds to the results of its first response and then to the results of that response and so on, human beings may be unable to leave off reacting to their own reactions, incorporating ever more elaborate layers into a production that then takes on shapes and features unimaginable from its modest beginnings.
What explains religion? Sweet tooth, symbiont, bower, money, pearl, or none of the above? Religion may include phenomena of human culture that have no remote analogue in genetic evolution, but if so, we will still have to answer the cui bono? question, because it is undeniable that the phenomena of religion are designed to a very significant degree. There are few signs of randomness or arbitrariness, so some differential replication has to pay for the R & D responsible for the design. These hypotheses do not all pull in the same direction, but the truth about religion might well be an amalgam of several of them (plus others). If this is so, we will not get a clear vision of why religion exists until we have clearly distinguished these possibilities and put each of them to the test.
If you think you already know which theory is right, you are either a major scientist who has been concealing a vast mountain of unpublished research from the rest of the world, or else you are confusing wishful thinking with knowledge. Perhaps it seems to you that I am somewhat willfully ignoring the obvious explanation of why your religion exists and has the features it does: it exists because it is the inevitable response of enlightened human beings to the obvious fact that God exists! Some would add: we engage in these religious practices because God commands us to do so, or because it pleases us to please God. End of story. But that could not be the end of the story. Whichever religion is yours, there are more people in the world who don’t share it than who do, and it falls to you—to all of us, really—to explain why so many have gotten it wrong, and to explain how those who know (if there are any) have managed to get it right. Even if it is obvious to you, it isn’t obvious to everyone, or even to most people.