There is a rather prosaically biological side to religious experience that has emerged only during the last decade. Many of the practices that religions enjoin on their followers are just the kind of activities that are likely to be good at stimulating the production of endorphins in the brain. Different religious traditions have, of course, placed different emphases on the kinds of activities that are deemed appropriate for religious observance, but it is striking that so many have placed so much emphasis on the infliction of physical pain and/or stress. These have included fasting, dancing or other rhythmic movements (think of the rhythmic bobbing of orthodox Jews praying at the Temple wall in Jerusalem, the repetitive counting of rosary beads and similar prayer devices), flagellation and the painful tasks imposed on pilgrims (such as walking the Stations of the Cross on one’s knees or, in the Buddhist and yogic traditions, long periods of sitting motionless in positions that are difficult to adopt), painful or stressful initiation rites in many tribal societies, communal singing (especially the tonally deep sustained forms that are typical of chanting, but also the lusty singing of hymns in the more evangelical traditions of Christianity), the intense rhythmically repetitive singing of the qawwali tradition in Sufi Islam, the long hours spent locked in services, the emotional rollercoaster induced by all the best charismatic preachers… The list could go on and on. All these practices impose low but persistent levels of stress on the body, and it is precisely this kind of persistent low-level stress that is particularly effective at stimulating the production of endorphins.

From Robin Dunbar’s The Human Story, London: Faber and Faber, 2004, pp. 172-173.