At dusk over a reed bed, tens of thousands of starlings fold and unfold across the sky as if one animal were breathing. No bird is in charge, and no bird can see the whole flock. When physicists filmed starling flocks over Rome and rebuilt them in three dimensions, they found that each bird tracks only six or seven of its closest neighbors, whatever the distance to them. The rolling shape comes out of simple local rules like that one, repeated across thousands of birds.
When a hawk attacks, a few birds swerve. Their neighbors swerve with them, then the neighbors’ neighbors, and the turn crosses the flock faster than any one starling could fly the distance. Close copying holds the flock together, and it is also how a swerve by a handful of birds becomes an escape.
Human groups hold together the same way, and they too have to decide what to do when a few members break formation. I look at that decision mostly through religion, where it is hardest to get right.
Three kinds of copying
“Conformity” gets used for at least three different things, and blurring them makes the case for human copying sound older and stronger than it is.
The first is looking like the others. Predators tend to single out the odd one in a group, so fish that look different from their school are targeted more often, and butterflies that share one warning pattern, like the Heliconius species of the American tropics, split the cost of teaching birds what not to eat. Natural selection does this copying, and no animal learns anything from its neighbors.
The second is moving with the others, as the starlings do. Each bird matches its neighbors’ heading and picks up no habit or belief from the flock.
The third is the one that matters here: taking up a behavior because many others have it. Biologists reserve “conformist learning” for the strong version, in which an animal adopts the majority’s choice even more often than the majority’s share would predict. Outside our species the evidence is real but thin. Nine-spined sticklebacks choose feeding patches in a way that tracks the majority. Wild great tits near Oxford, seeded with one of two ways to open a puzzle box, kept their local method into the next year, and most birds that moved to another part of the wood switched to the method used there.
In theory, copying the majority pays when finding things out for yourself is costly or unreliable and the world changes slowly enough that what most others learned is still true. When the world changes fast, the majority is a record of yesterday.
Humans copy more than any other animal, and we choose whom to copy: people with prestige, people who seem to be succeeding, and people whose actions show they believe what they say. We also go along less than the textbooks imply. In Solomon Asch’s line-judging experiments of the 1950s, three in four students yielded to a unanimous wrong answer at least once, but about two-thirds of their answers on those trials were correct. Asch put independence first in the title of his report, and Hugo Mercier’s Not Born Yesterday makes the larger case that people are hard to fool.
Going along without agreeing
Plenty of conformity is harmless. Indians drive on the left and Germans on the right, and nobody in either country privately wishes they were on the other side.
The cases worth worrying about have a gap between what people think and what they do. In a study published in 2020, economists surveyed young married men in Riyadh. Most privately supported women working outside the home but underestimated how many of their peers agreed, and men shown the real figure became more likely to sign their wives up for a job-matching service. A norm few of these men wanted was propped up partly by their guesses about each other.
Psychologists call this pluralistic ignorance. The economist Timur Kuran called the behavior that sustains it preference falsification, and argued that it is why the revolutions of 1989 in Eastern Europe surprised almost everyone, including many of the people who made them. Whether anyone follows the first person to speak up depends less on whether the speaker is right than on whether listeners can see they are not alone.
Slow evidence
Most beliefs meet the world quickly. A wrong idea about which mushrooms are safe, or how much load a bridge can carry, gets corrected, sometimes brutally. Many religious claims get their evidence slowly, perhaps not in this life, and in forms an outsider can’t check on demand: an answered prayer, a changed life, a presence felt in worship. Economists call goods whose quality you can’t check even after buying them credence goods. You can test a hammer in a minute. You can’t test salvation on a Wednesday.
This is the extreme case of the condition under which copying pays, since finding out for yourself is not just costly but impossible on demand. So people check each other. The anthropologist Joseph Henrich argued that we trust a teacher’s words more when the teacher’s actions would cost a nonbeliever dearly. He called these credibility-enhancing displays. A preacher who gives away her fortune persuades more than one who only talks about giving, and a martyr persuades more than either.
Copying credible people explains something majority copying can’t: how a faith gets started. Copying the majority would have kept the Roman Empire pagan. Christianity began as a small minority, and Rodney Stark estimated, in an argument historians still contest, that it grew by something like forty percent a decade, along networks of family and friends, made credible by people visibly willing to pay for it. Pippa Norris and Ronald Inglehart argue that faith also recedes as life becomes more secure, so copying is one force among several.
Costly demands also bind the people already inside. Richard Sosis and Eric Bressler studied eighty-three American communes of the nineteenth century. The religious communes outlasted the secular ones, and the religious communes that demanded more of their members, from food taboos to celibacy, tended to last longer. Among the secular communes, more demands made no difference. Laurence Iannaccone had made the general case years earlier: strict churches are strong because their demands screen out free riders.
I draw mostly on Christian history because its dealings with dissenters are unusually well documented, and bring in Jewish and Islamic practice where they handled the problem differently. None of this says whether any faith is true. True and false ideas spread by the same routes.
Orders and sects
Around 1173 Valdes, a rich merchant of Lyon, gave away his property and began preaching poverty in the streets. A generation later Francis, the son of a rich cloth merchant of Assisi, did much the same. Both wanted voluntary poverty, preaching in the common tongue, and a return to the life of the apostles, and both sought the pope’s approval.
In 1179 Alexander III approved the poverty of Valdes and his followers but forbade them to preach without the local clergy’s permission. They preached anyway, and in 1184 a decree of Lucius III condemned them as heretics. Francis accepted the Church’s terms, and around 1209 Innocent III approved his brotherhood. The Franciscans became one of the great orders of the Church, and the Waldensians were persecuted for centuries.
The outcome turned on the popes as well as the preachers. The same decree of 1184 condemned the Humiliati, a lay penitential movement from Lombardy, and in 1201 Innocent III gave them a rule and took them back, once they accepted his terms. More than six centuries later, Thomas Babington Macaulay, a Protestant writing with reluctant admiration in his review of Leopold von Ranke’s History of the Popes, named this as one important part of Rome’s policy: it knew what to do with enthusiasts. It gave them a coarse gown and a rope and sent them out to teach in its name. The Church of England had no such place for John Wesley, who lived and died an Anglican priest, and the Methodists became a separate church.
Since Francis and Valdes barely disagreed about poverty, what Rome tested was obedience, and that went deep: whether a layman may preach without the bishop’s leave is a question about what the Church is, and for Francis obedience was itself part of holiness. Even inside the order there were limits. In 1318 four Franciscans who would not give up their strict reading of poverty were burned at Marseille.
From the institution’s side, a test of obedience is sensible. Obedience is easy to observe, and truth in matters of faith is not. But such a test can only tell a loyal reformer from a defiant one. It cannot tell a dissenter who has seen something real from one who is wrong. It also hides how many people privately agree with the dissenter, since agreeing aloud is itself a kind of disobedience.
A starling flock never needs a test like this. It follows every swerve, false alarms included, because a false alarm costs a wingbeat. A church that followed every dissenter would come apart, so it has to sort them, and it will often sort them wrongly.
A route back
Science sorts its dissenters too. Alfred Wegener proposed in 1912 that the continents had drifted apart, and most geologists rejected the idea for half a century. He died on the Greenland ice in 1930 with the question open. A few geologists, among them Alexander du Toit in South Africa and Arthur Holmes in Britain, kept the idea alive until surveys of the ocean floor in the 1950s and 1960s found stripes of magnetized rock that made sense only if the floor was spreading. Geology needed somewhere for the rejected idea to survive, and evidence that eventually arrived.
Religious evidence is slower and more disputed, but churches do change their minds. In 1864 Pius IX’s encyclical Quanta Cura condemned the opinion that liberty of conscience and worship is each person’s own right, to be guaranteed by law. In the 1950s the American Jesuit John Courtney Murray was told to stop publishing on religious freedom. In 1965 the Second Vatican Council declared religious freedom a right grounded in human dignity, and Murray had helped to draft the declaration. He had been silenced, but he had not been expelled, and his argument was still there when the Church was ready for it.
A tradition can keep rejected views alive in two places. One is inside. The Mishnah records minority opinions alongside the majority’s rulings, and gives as one reason that a later court may find a minority view sound and rely on it. Sunni Islam came to accept four schools of law as legitimate, which gave lasting disagreement over law a home within the faith. The other place is outside. The Waldensians held on in the valleys of the Alps, and Wesley’s followers became one of the largest Protestant traditions in the world. In 1975 the Waldensian church in Italy united with the Italian Methodists, two churches descended from dissenters their mother churches could not hold.
None of this shows that the survivors were right. Survival proves only that a view had somewhere to go. The case for giving it somewhere is that the question stays open long enough for slow evidence, of whatever kind a tradition accepts, to arrive.
The price of leaving
The outside route is only as good as the price of leaving. A great deal of religious uniformity in history was plain compliance. After the Peace of Augsburg in 1555, the princes of the Holy Roman Empire chose between Catholicism and Lutheranism for their lands, and their subjects were expected to follow. But the settlement let Catholic and Lutheran subjects who refused sell their property, settle what they owed their lord, and emigrate, though serfs still needed their lord’s leave. It was grudging and narrow (Calvinists had no standing until 1648), but it conceded that a dissenter needed somewhere to go.
Two costs usually get lumped together here. One is what membership demands: the fasts, the tithes, the hours. The evidence from communes and strict churches is about this cost. The other is what leaving costs: shunning, the loss of family and livelihood, and in some centuries, life. Some demands do both jobs, since property handed to a commune is property a leaver goes without. But nothing in the evidence for strictness says the second cost has to be high. A community can ask a great deal of the people who stay and still let the ones who go leave whole.
Albert Hirschman saw a catch in Exit, Voice, and Loyalty. When leaving is easy, the members who care most about quality tend to go first, and the institution loses the voices that might have reformed it. That is real, and easy leaving has other victims, such as the old and the poor left behind in emptying congregations. But voice depends on safety too. A dissenter who expects to be ruined for speaking will stay quiet or go, and either way the institution hears nothing.
Apostasy is still a crime in about twenty countries, and in some close-knit groups leaving still costs a person their family. If I have to choose, I would rather a community keep its demands and lower the penalty for walking away. A congregation weakened by easy leaving still exists and can still make its case. A dissent suppressed with no one left to carry it is usually gone.
The hawk you can’t see
In a murmuration the hawk shows itself within a second, so the birds that turned first are proved right almost as soon as they turn. Human groups rarely get that. A congregation, a party, a company, or a scientific field spends most of its life with the hawk out of sight, deciding whether the members who swerved saw something real. It will often guess wrong. A group can recover from its wrong guesses if the people it gave up on, and the views they carried, are still somewhere when the hawk finally appears.
Most dissenters are wrong. A group that will not let any of them live may never learn which ones were right.
Sources
- Michele Ballerini and colleagues, “Interaction ruling animal collective behavior depends on topological rather than metric distance: evidence from a field study” (2008)
- Alessandro Attanasi and colleagues, “Information transfer and behavioural inertia in starling flocks” (2014)
- Thomas Pike and Kevin Laland, “Conformist learning in nine-spined sticklebacks’ foraging decisions” (2010)
- Lucy Aplin and colleagues, “Experimentally induced innovations lead to persistent culture via conformity in wild birds” (2015)
- Peter J. Richerson and Robert Boyd, Not by Genes Alone (2005)
- Joseph Henrich, The Secret of Our Success (2015)
- Solomon Asch, “Studies of independence and conformity: I. A minority of one against a unanimous majority” (1956)
- Hugo Mercier, Not Born Yesterday (2020)
- Leonardo Bursztyn, Alessandra González, and David Yanagizawa-Drott, “Misperceived social norms: women working outside the home in Saudi Arabia” (2020)
- Timur Kuran, Private Truths, Public Lies (1995)
- Joseph Henrich, “The evolution of costly displays, cooperation and religion: credibility enhancing displays and their implications for cultural evolution” (2009)
- Rodney Stark, The Rise of Christianity (1996)
- Pippa Norris and Ronald Inglehart, Sacred and Secular (2004)
- Richard Sosis and Eric Bressler, “Cooperation and commune longevity: a test of the costly signaling theory of religion” (2003)
- Laurence Iannaccone, “Why strict churches are strong” (1994)
- Herbert Grundmann, Religious Movements in the Middle Ages (1935)
- Thomas Babington Macaulay, review of Leopold von Ranke’s History of the Popes, Edinburgh Review (1840)
- Pius IX, Quanta Cura (1864)
- Second Vatican Council, Dignitatis Humanae (1965)
- Mishnah, tractate Eduyot, chapter 1
- Albert O. Hirschman, Exit, Voice, and Loyalty (1970)