My wife Anne and I have accumulated an assortment of mugs that occupy a shelf of our kitchen cabinet. All of them perform the same function of holding hot liquid, but we seem to have developed a complex system for using them. Rather than grabbing any two for our morning coffee, I feel impelled to pair them with each other.

A mug with a crow on it–the species that Anne studies–gets paired with Coast Guard mug bearing a quote from one of my father’s books. An earthenware mug with a fox on it–which Anne doesn’t study–is nevertheless used only by Anne and is paired with an earthenware pot bellied mug that is used only be me. Other mugs aren’t used at all, especially the glazed ones without images. Past favorites with their handles broken line the back of the shelf. We don’t use them, but we don’t get rid of them. Why?

Then there is a set of four mugs bearing the images of folk art farm animals; a horse, a cow, a sheep, and a pig. Not only do Anne and I use these mugs interchangeably, but we make a game of who gets what on any particular day. Does she want to be the fleet horse or the productive cow? Do I want to be the pig wallowing in happiness, or the contentedly grazing sheep?

We also use different mugs for coffee and tea. I probably spend several hours a year thinking about my mugs–a small but significant entry in my time budget.

Why can’t I just grab any two mugs for the morning coffee? I don’t think that there is any function to the complex system that Anne and I have created. Instead, I think that the human mind imposes meaning on anything that it turns its gaze upon. Sometimes the meaning-making results in something useful, sometimes in something capricious, but there is no way to turn it off. We’re a meaning-making species and there’s nothing we can do about it.

Religions are meaning systems far more elaborate than the meaning system that I have developed for my mugs. It might seem silly even to compare them, but evolutionists who study religion ask the same basic question about whether it is functional or a byproduct of mental operations that evolved for other reasons. Of course, there is no single “it” when it comes to religion, which is an exceedingly fuzzy set of beliefs and practices.

In my 2002 book Darwin’s Cathedral, I argued that most enduring religions are eminently functional for the community of religious believers, much as Emile Durkheim postulated over a century ago. Unlike the meaning system that I developed for my mugs, religious meaning systems are pounded into shape by the anvil of natural and cultural selection. At the time, I was outnumbered by evolutionist colleagues who favored a byproduct interpretation of religion and the positions were argued in an either/or fashion. Now I think that we are reaching a consensus that leaves room for both positions, as described in this recent review by Scott Atran and Joe Henrich.

Most enduring religions generate deep commitments to prosociality within the religious community, but they are cobbled together from genetic and cultural adaptations that often originally evolved for other purposes. Francois Jacob famously described evolution as a tinkerer that builds new structures out of old parts, and this is true for the cultural evolution of symbolic meaning systems, no less than genetic evolution. The meaning of my mugs has no meaning, but it says a lot about meaning systems that do.