Editing Signalling theory (section)

=== Religion ===
{{anchor|Religion as a costly signal}}
{{further|Evolutionary psychology of religion}}
[[File:Handling of serpents, a part of the ceremony at the Pentecostal Church of God. This coal camp offers none of the... - NARA - 541340.jpg|thumb|upright|left|Religious rituals such as [[Snake handling in religion|snake handling]] may be explainable as costly signals.]]

Costly religious rituals such as [[genital modification]], [[Fasting|food and water deprivation]], and [[Snake handling in religion|snake handling]] look paradoxical in evolutionary terms. Devout religious beliefs wherein such traditions are practiced appear maladaptive.{{sfn|Tuzin|1982}} Religion may have arisen to increase and maintain intragroup cooperation.{{sfn|Steadman|Palmer|2008}} Cooperation leads to altruistic behaviour,{{sfn|Bulbulia|2004}} and costly signalling could explain this.{{sfn|Zahavi|1975}} All religions may involve costly and elaborate rituals, performed publicly, to demonstrate loyalty to the religious group.{{sfn|Irons|2001}} In this way, group members increase their allegiance to the group by signalling their investment in group interests. However, as group size increases among humans, the threat of free riders grows.{{sfn|Barrett|Dunbar|Lycett|2002}} Costly signalling theory accounts for this by proposing that these religious rituals are costly enough to deter free riders.{{sfn|Iannaccone|1992}}

Irons proposed that costly signalling theory could explain costly religious behaviour. He argued that hard-to-fake religious displays enhanced trust and solidarity in a community, producing emotional and economic benefits. He showed that display signals among the [[Yomut]] [[Iranian Turkmen|Turkmen]] of northern [[Iran]] helped to secure trade agreements. These "ostentatious" displays signalled commitment to Islam to strangers and group members.{{sfn|Irons|1996}} Sosis demonstrated that people in religious communities are four times more likely to live longer than their secular counterparts,{{sfn|Sosis|2000b}}{{sfn|Bulbulia|2004}} and that these longer lifespans were positively correlated with the number of costly requirements demanded from religious community members.{{sfn|Sosis|Bressler|2003}} However, confounding variables may not have been excluded.{{sfn|Hood|Hill|Spilka|2009}} Wood found that religion offers a subjective feeling of well-being within a community, where costly signalling protects against free riders and helps to build self-control among committed members.{{sfn|Wood|2016}} Iannaccone studied the effects of costly signals on religious communities. In a self-reported survey, as the strictness of a church increased, the attendance and contributions to that church increased proportionally. In effect, people were more willing to participate in a church that has more stringent demands on its members.{{sfn|Iannaccone|1992}} Despite this observation, costly donations and acts conducted in a religious context does not itself establish that membership in these clubs is actually worth the entry costs imposed.

Despite the experimental support for this hypothesis, it remains controversial. A common critique is that devoutness is easy to fake, such as simply by attending a religious service.{{sfn|Rees|2009}} However, the hypothesis predicts that people are more likely to join and contribute to a religious group when its rituals are costly.{{sfn|Iannaccone|1992}} Another critique specifically asks: why religion? There is no evolutionary advantage to evolving religion over other signals of commitment such as nationality, as Irons admits. However, the reinforcement of religious rites as well as the intrinsic reward and punishment system found in religion makes it an ideal candidate for increasing intragroup cooperation. Finally, there is insufficient evidence for increase in fitness as a result of religious cooperation.{{sfn|Bulbulia|2004}} However, Sosis argues for benefits from religion itself, such as increased longevity, improved health, assistance during crises, and greater psychological well-being,{{sfn|Sosis|2003}} although both the supposed benefits from religion and the costly-signaling mechanism have been contested.{{sfn|Schuurmans-Stekhoven|2016}}