Hearth and Campfire Influences on Arterial Blood Pressure: Defraying the Costs of the Social Brain Through Fireside Relaxation

The importance of fire in human evolutionary history is widely acknowledged but the extent not fully explored. Fires involve flickering light, crackling sounds, warmth, and a distinctive smell. For early humans, fire likely extended the day, provided heat, helped with hunting, warded off predators and insects, illuminated dark places, and facilitated cooking. Campfires also may have provided social nexus and relaxation effects that could have enhanced prosocial behavior. According to this hypothesis, calmer, more tolerant people would have benefited in the social milieu via fireside interactions relative to individuals less susceptible to relaxation response. Using a randomized crossover design that disaggregated fire's sensory properties, pre-posttest blood pressure measures were compared among 226 adults across three studies with respect to viewing simulated muted-fire, fire-with-sound, and control conditions, in addition to tests for interactions with hypnotizability, absorption, and prosociality. Results indicated consistent blood pressure decreases in the fire-with-sound condition, particularly with a longer duration of stimulus, and enhancing effects of absorption and prosociality. Findings confirm that hearth and campfires induce relaxation as part of a multisensory, absorptive, and social experience. Enhancements to relaxation capacities in the human social brain likely took place via feedback involving these and other variables.