I live in Santa Fe, New Mexico. Each spring, I know Holy Week is approaching when I start to see people walking along the side of Highway 285. Wearing matching group t-shirts and carrying crosses, these are pilgrims en route to El Santuario de Chimayo, a nineteenth century Roman Catholic church nestled in the hills north of Santa Fe. Tens of thousands make the journey each year, fulfilling vows and seeking blessings at the pilgrimage site.
When I pass these pilgrims on the road, I always reflect on their endurance. One year, I joined in the pilgrimage for the last few miles and returned home with sore feet and tired muscles. Recalling my own fatigue, I wince for those I pass, knowing that some have come from as far as Albuquerque, ninety miles to the south. These people must have a strength that I do not, I’ll reflect as I drive comfortably by with the AC on. That strength must not only be physical, but mental, too. They must have conviction, I’ll surmise. They must be driven forward by their faith and by one another. As I drive past, I can’t help but attribute all of this and more to the people resolutely making their way up the road. With just a fleeting glimpse, I am apparently ready to infer all sorts of qualities and characteristics about the blur of pilgrims I pass.
You might think me particularly judgmental, but I’m not alone in making these many presumptions about others. As Cristina Moya recently wrote for TVOL,1 humans are eminent stereotypers. It seems, too, that we often use religious action, especially impressive action like what these pilgrims are doing, to infer something about the character and commitments of others. Experimental studies have found, for example, that we see people as more trustworthy if they show signs of membership to a religious community (say, a necklace with a cross)2 or adhere to religious dietary requirements (say, eating halal).3 Only those who are truly committed to the religious group and its beliefs, we seem to reason, will be willing to make such investments. They must be trustworthy.
This idea, that religious action reveals religious commitment, builds on the insights of signaling theory, a body of theoretical work first hit upon by both evolutionary biologists and economists in the 1970s. These scholars argued first that it’s hard to have confidence in the quality and intentions of others. One way to have some confidence, they suggested, is if there are signals that only an individual who honestly has the underlying quality or commitment is able to give. Their examples are broad: a peacock with a particularly luxurious tail signals his high genetic quality.4 A job applicant with a university degree signals ample intelligence and connections for the job.5 Applying signaling theory to religion, we can see the religious acts that people carry out as potential signals of their commitment to the religious and moral precepts of the community.6,7
So, are religious actions are being used as signals of an individual’s commitments? Am I alone in attempting to discern something about the commitments of strangers I pass on the road? What is it, exactly, that people infer from the religious actions of others?
To answer these questions, I did the obvious thing: I went to live in South India for two years. In the villages where I conducted ethnographic fieldwork, there are a mix of different religious communities – not only Hindus, but also Catholics and Protestants. Residents there often undertake impressive acts in the name of their faith: they go on pilgrimages there, too, sometimes barefoot, to the Hindu temple at Palani or the Catholic church at Vailankanni; they fulfill religious vows by piercing their bodies with hooks and spears or walking across a bed of hot coals; they sacrifice animals; and they even become possessed by the divine. What might onlookers discern about the commitment of these individuals when they see them performing such acts of devotion? To figure this out, I compiled records of people’s religious practice and gathered information on how villagers perceived one another. I asked people to tell me who in the village they thought had various qualities, such as being devout, strong, generous, influential, and hardworking. Building on previous experimental work and drawing insights from signaling theory, I thought that those people who invested more in the religious life of the village – going on pilgrimages, visiting churches or temples, etc. – would be seen in a particularly good light by their peers.8
I found that this was true: those who worship regularly at a church or temple and those who undertake dramatic acts of devotion were seen by their peers as more devout. This certainly makes sense: people who did more religious acts were seen as more religious. But even more was being associated with such religious villagers: they were also seen as having a good work ethic, giving good advice, being generous, and having good character. A whole suite of other-focused, prosocial qualities was being attributed to those villagers who invested in the religious life of their village. On top of that, it was clear that these were some particularly discerning observers: they gave more recognition to those who were demonstrating multiple different types of religious action (not only going on a pilgrimage, perhaps, but also going to the temple each week). And, they paid particular attention to the religious action of young people, whom they were still trying to suss out. So, onlookers – like me driving past the pilgrims in Santa Fe, and like the villagers in South India – are astute observers, shaping their perception of others in light of their religious action, especially those acts that make serious demands of the devotee.
This evidence that a person’s religious action shapes how others perceive him or her might help us better understand why we see such impressive forms of religious devotion the world over. When I drive past the Chimayo pilgrims or watch my South Indian interlocutors boldly stride across the glowing bed of hot coals, I may at first wonder why they would be undertaking such a daunting, painful, risky act. By even asking that question, I’ve already started to answer it. My very response – all that I infer about the character, commitments, and convictions of that devotee – stems from how daunting and risky that religious act is. Undertaking such an act, then, reliably conveys something about that person’s moral commitments to others. By building others’ confidence in his/her actions and intentions, he/she may then be better able to establish strong, trusting relationships with others. The long, arduous walk to Chimayo may result not only in divine assistance, but also in tangible assistance from friends, family, and acquaintances. Those very things that can make religion seem particularly inscrutable for some may actually be what make it such an enduring and resilient part of the cultures of the world.
 McCullough, M. E., Swartwout, P., Shaver, J. H., Carter, E. C., & Sosis, R. (2016). Christian religious badges instill trust in Christian and non-Christian perceivers. Psychology of Religion and Spirituality, 8(2), 149–163.
 Hall, D. L., Cohen, A. B., Meyer, K. K., Varley, A. H., & Brewer, G. A. (2015). Costly signaling increases trust, even across religious affiliations. Psychological Science, 26(9), 1368–1376.
 Zahavi, A. (1975). Mate selection: A selection for a handicap. Journal of Theoretical Biology, 53(1), 205–14.
 Spence, M. (1973). Job market signaling. The Quarterly Journal of Economics, 87(3), 355–374.
 Sosis, R., & Alcorta, C. S. (2003). Signaling, solidarity, and the sacred: The evolution of religious behavior. Evolutionary Anthropology, 12(6), 264–274.
 Henrich, J. (2009). The evolution of costly displays, cooperation and religion: credibility enhancing displays and their implications for cultural evolution. Evolution and Human Behavior, 30(4), 244–260.
 Power, E. A. (2017). Discerning devotion: Testing the signaling theory of religion. Evolution and Human Behavior, 38(1), 82–91.