Why Religions Ban Pork and Alcohol: Understanding Costly Signalling

The Weirdness of Religion

Throughout history, religious institutions have banned absurd and seemingly arbitrary things: Christians shouldn't work on the Sabbath, Jews shouldn't eat pork, Muslims shouldn't drink alcohol, Hindus shouldn't harm cows, and Buddhists shouldn't point their feet at the Buddha. While cultural explanations attribute these prohibitions to impurity or impiety, they fail to answer the underlying question: why is this particular item impure?

The bizarre choices have led anthropologists to theorize that, for a religion to be successful, it doesn't matter what is banned as long as something is. They propose something called “costly signalling theory” in which a person endures a "costly" prohibition to "signal" to others that they are devout and trustworthy. Besides bans, costly signals include ritual practices (see below) and markers of affiliation (cross, kippah, burqa, etc.).

Rituals can be particularly costly. In Papua New Guinea, young males have their private parts forcibly lacerated by stinging nettles, while Hindus have a ritual that involves dragging carts attached by hooks to their skin. Other rituals are merely bizarre, although just as time-consuming. For example, Mbuti pygmies have a festival that transforms a rusty old pipe into a sacred flute, while Catholics transform bread into the body of the Messiah.

The most ubiquitous costly signals are markers of affiliation, or badges, which include special clothing, jewellery, tattoos, and grooming habits. For example, Jews wear a kippah (skull cap), Sikhs don't cut their hair, Muslim women wear burqas, Polynesians display tattoos, and Christians wear crucifixes.

For an evolutionary biologist, these badges, bans, and behaviours might look like a waste of time, energy, and resources (e.g., burning food on an altar instead of eating it). How could they have evolved when our species needed to gather food, find shelter, and defeat enemies? One explanation is that the signals display a person's faith, commitment, and group affiliation. Indeed, the signals are noticeable and public, suggesting that they are designed to communicate a message.

Costly Signalling Theory

Anthropologists such as Richard Sosis and Joe Bulbulia think that costly signalling theory can explain these unusual behaviours, and that it doesn't matter what specific thing is banned, worn, or performed, as long as it is:

1. Costly. It requires effort, time, or resources to perform or maintain. This dedication is difficult for nonbelievers to fake.

2. Noticeable. It comes up in daily life (e.g., refusing to eat pork at a restaurant) or it is highly important at a particular time (e.g., an annual festival).

3. Bizarre. It can only be attributed to a religious function (e.g., pleasing to a deity) and not to any mundane function.
   
   

They propose that the signals evolved because they increase within-group cooperation; a benefit that outweighs the cost of performing the signals. Indeed, most religions include morals that promote cooperation (e.g., love thy neighbour and don't murder or steal) and a costly signal of commitment to a religion may therefore establish trust in a person's adherance to this moral code. For example, even secular New Yorkers prefer Mormon nannies.

Cooperation within a society would have been the difference between survival and oblivion. A society full of free-riders would collapse. Costly signals would have provided a more effective tool than spoken promises to weed them out, as free-riders find such signals difficult or undesirable to fake.

Evidence for Costly Signalling Theory

Researchers have examined whether groups with high membership demands (i.e., more costly signalling) enjoy high levels of devotion and commitment. One study found that such groups grow at a faster rate and have more committed members than groups with low membership demands, and that religious "bizarreness" is associated with attendance at services.

Similarly, surveys have found that Muslims, Mormons, Baptists, and Seventh Day Adventists have added to their numbers quicker than liberal Protestant churches, while the liberalization of the Catholic Church in the 1960s appears to have accelerated its decline.

Other studies have tested for more direct effects on cooperation. For example, an examination of 83 early American communes found that surviving communes were more likely to be religious and to impose costly requirements on their members (e.g., celibacy, or giving up material possessions).

A similar study found that the collapse of the “kibbutz” (commune) movement in Israel was largely limited to secular communes. Most of the religious communes survived and remained profitable after imposing costly signals on their members (e.g., not doing business on the Sabbath), with signalling associated with higher levels of cooperation.

Haredi Jews are another illustrative example. They came to Israel from Russia but continued to wear thick clothing and fur hats in the desert sun. It became a costly signal of their faith: why would they suffer the heat unless they truly believed? The signal facilitated a remarkable level of cooperation: even when complete strangers, Haredi Jews open their houses to each other, lend their cars, and provide interest-free loans.

The General Features of Costly Signals

Costly signals were not invented to explain nonsensical religious behaviors. In fact, there are many types of costly signal between humans (e.g., signals of wealth, status, skill, attractiveness, emotional need, and willingness to fight) and between social animals such as elephants. The technical definition requires that these signals:

1. Communicate something that varies within a population (e.g., levels of commitment).

2. Benefit the receiver of the signal with reliable information (e.g., knowing who to trust and cooperate with).

3. Benefit the sender of the signal (e.g., people cooperate with them) such that others may be tempted to fake the signal if they can endure the cost of sending it.

4. Are costlier for people who lack what is being communicated (e.g., religious commitment). In the case of religion, believers may have already conformed to a lifestyle that makes sending the signal easier (e.g., giving up vices may be more difficult for sceptics).
   
   

The costly signalling theory of religion only concerns one case of costly signalling within one species, but it meets the general definition.

What is Special About Bans? Why Pork and Alcohol?

In contrast to rituals and badges, bans are only useful as signals when they are at risk of being transgressed. It follows that, the more difficult a banned item is to give up (pork, alcohol, sex, gambling, etc.) the more effective it is at weeding out free-riders or nonbelievers. Thus, although anything could conceivably be banned, these types of bans are the costliest signals to send.

How do Religious Beliefs fit in?

Religious beliefs should reinforce the cooperative benefits of costly signalling. For example, if you believe that performing a ritual rewards you with divine protection, your likelihood of performing it increases, which increases its real benefits (cooperation). This is important because the real benefits are less likely to be acknowledged than the perceived supernatural benefits.

Policing behaviour in a large society also becomes easier when enforcers only need to police the public observance of costly signals. Thus, the cooperative benefits of a belief in afterlife judgement, which causes people to police behaviour because they think it is being watched and judged by a deity, are easier to realize with costly signalling. 

Remarkably, signalling theory proposes that using costly signals can even generate religious belief. For example, nonbelievers who dishonestly utilize a signal (e.g., going to Church for social benefits rather than to worship) experience an unpleasant state of “cognitive dissonance”—a conflict between their beliefs and their repeated, public actions,—which forces a resolution: either start believing or stop going to Church.

Studies of cults suggest that the resolution is usually to “start believing.” Cults appear to introduce new members to costly signalling (e.g., leafletting on the street, or participating in group activities) before successfully brainwashing them with the cult's idiosyncratic teachings.

Indeed, costly signalling may elicit emotions that make associated beliefs more compelling. For example, a “religious experience” can be perceived as “more real” than reality, while singing in synchrony with a group can produce positive emotions that facilitate identification with the group's beliefs. If, however, nonbelievers remain unconvinced, they cannot fake the involuntary emotions underpinning the signal’s reliability.

Closing Remarks

Although costly signalling theory can explain many features of religious practice, including why it endures, it does not explain why individuals choose to form the specific beliefs that are the basis for these behaviours.

For example, why do religious beliefs address existential questions and concerns? Why are they shaped or constrained by particular psychological biases? Cognitive and motivational explanations for religion are better placed to answer these questions.

The most that signalling theory can say is that some of these biases and motivations came to be favoured and potentially shaped by natural selection because they resulted in behaviours that helped us to cooperate.

In other words, evolutionary explanations for religion can describe why a practice endures, but not why it came to be, or how it works in the brain. Indeed, signalling theory applies to many aspects of human and animal life, and its explanation for religion can only ever be a general one.