The Mu-Opioid of the People
: Rituals and the Psychobiology of Social Bonding

  • Sarah Charles

    Student thesis: Doctoral ThesisDoctor of Philosophy


    Group living is one of the most, if not the most, significant development in human evolution. It is our ability to live in groups, and act as social animals, that has helped us not just survive, but thrive over millennia. However, group living comes with time and energy costs as well as benefits. Humans have evolved a ‘bonding toolkit’ (a suite of behavioural and affective mechanisms) by which social bonding is more easily enabled. The elicitation of positive affective states, as outlined in the ‘Broaden and Build’ theory, is thought to be one major part of this bonding toolkit. Yet, the neurochemical underpinnings of the bonding toolkit are less well-understood. The brain-opioid theory of social attachment claims that the behaviours and positive affective states that make up the bonding toolkit rely heavily on the endogenous opioid system, especially mu-opioids, to cause bonding.

    Sociologists and anthropologists have noted for over a century that religious rituals appear to reliably lead to social bonding. More recently, psychologists have suggested this is because religious rituals include or evoke several behaviours and affective states that are part of the bonding toolkit (e.g., shared goals, positive affect, and synchronised movement). However, little research has yet been conducted to explicitly assess the psychobiological mechanisms underlying the role of religious ritual in social bonding.

    In this thesis, the major question I sought to answer was “what are the psychobiological mechanisms underlying social bonding caused by religious ritual?” To answer this question, I conducted five studies, across both naturalistic settings and controlled conditions, with UK and Brazilian populations. The first of these studies, an international field study which included 24 ritual sites, provided support for the ‘Broaden and Build’ theory as well as for the brain-opioid theory of social attachment. Additionally, I found an unforeseen mechanism – a connection to something bigger than oneself – predicted levels of social bonding in those attending ritual. However, results on the role of religiosity on the strength of the bonding effect were inconsistent.

    To help address these inconsistent findings, two studies that compared religious ritual to behaviourally similar (study two, in a naturalistic setting) or behaviourally identical (study three, in controlled conditions) secular ritual. These studies directly assessed the role of the religious component of ritual on social bonding. The findings from these studies demonstrate that the positive affect and connection to something bigger mechanisms play a significant role in social bonding both in those attending religious rituals and those attending secular rituals. This suggests that, while the exact nature (secular or spiritual) of the ritual does not play a role in social bonding, rituals that are better able to create a feeling of connection to something bigger than oneself, be they secular or not, are better able to produce social bonding.

    However, in study three, evidence collected via a proxy measure of mu-opioids did not provide support for the brain-opioid theory of social attachment. To address the inconsistency between the results from study one and study three, two follow-up placebo-controlled, double-blind studies using Naltrexone, a mu-opioid antagonist, were conducted as a more direct method of assessing the role of mu-opioids in ritual social bonding. In both studies, there was a significant interaction effect of pill type (placebo compared to Naltrexone) and time (before compared to after the ritual). This demonstrated that mu-opioids play a necessary role in the way rituals lead to social bonding.

    As part of this thesis, I also addressed a gap in the literature highlighted in past research: the lack of a reliable measure of quality/strength of a social bond. I addressed this gap by producing a novel, reliable and valid measure of social bonding that measures the quality of a bond. The findings from this thesis, alongside the contribution to the social bonding methodological toolkit, provide a significant contribution to the psychology of religion, and the psychobiology of social bonding fields.
    Date of AwardJan 2022
    Original languageEnglish
    Awarding Institution
    • Coventry University
    SponsorsTempleton Religion Trust
    SupervisorValerie van Mulukom (Supervisor) & Miguel Farias (Supervisor)

    Cite this