Behavioral and Brain Sciences, Volume 25, Number 4 (August 2004)
This paper proposes that human expression of pain in the presence or absence of caregivers, and the detection of pain by observers, arise from evolved propensities. The function of pain is to demand attention and prioritise escape, recovery and healing; where others can help achieve these goals, effective communication of pain is required. Evidence is reviewed of a distinct and specific facial expression of pain from infancy to old age, consistent across stimuli, and recognizable as pain by observers. Voluntary control over amplitude is incomplete, and observers better detect pain which the individual attempts to suppress than to amplify or to simulate it. In many clinical and experimental settings, facial expression of pain is incorporated with verbal and nonverbal-vocal activity, posture and movement in an overall category of pain behaviour. This is assumed by clinicians to be under operant control of social contingencies such as sympathy, caregiving, and practical help; thus strong facial expression is presumed to constitute an attempt to manipulate these contingencies by amplification of the normal expression. Operant formulations support skepticism about the presence or extent of pain, judgements of malingering, and sometimes the withholding of caregiving and help. However, to the extent that pain expression is influenced by environmental contingencies, “amplification” could equally plausibly constitute release of suppression according to evolved contingent propensities which guide behaviour. Pain has been largely neglected in the evolutionary literature and that on pain expression, but an evolutionary account can generate improved assessment of pain and reactions to it.