Negativity bias: An evolutionary hypothesis and an empirical programme

Abstract

Across many psychological domains there is evidence of negativity bias: the greater subjective potency of negative events when compared with positive events of the same objective magnitude. Here I propose a general evolutionary explanation for the phenomenon: the concave fitness-state (CFS) hypothesis. The CFS hypothesis proposes, with evidence from feeding, drinking and economic domains, that various motivational, emotional and cognitive states – through which stimuli activate responses – have a concave downwards (diminishing returns) relationship with fitness. Where this is the case it follows that a reduction in state, due to a negative stimulus, reduces fitness more than a positive stimulus of equal objective magnitude increases it, producing – the hypothesis consequently predicts – a negativity bias due to the difference in subjective stimulus potency. In discussing other approaches to understanding the phenomenon I critique the proposal that negativity bias can be explained as an adaptive response to the particular importance and urgency of dealing with threat, by arguing that: (1) where negative stimuli interpretable as threat, and contrasting positive stimuli, cannot be measured in a commensurate manner they cannot be validly tested for negativity bias; and (2) since threat stimuli and positive stimuli generally impact different states a greater potency for threat stimuli should generally be interpreted in terms of motivational competition rather than negativity bias. I suggest two ways of circumventing the problem of incommensurate stimuli when studying stimulus bias. The first is to use the loss aversion paradigm: rating the value of the same stimulus when presented as either a gain or a loss in relation to a reference value. Second, understanding the relative subjective potencies of positive and negative stimuli across a range of objective stimulus magnitudes, even when incommensurate, can be achieved experimentally by finding pairs of positive and negative stimuli which, though measured on different scales of magnitude, are equipotent. That is, they have equal and opposite effects on fitness, well-being or stimulus evaluation. These stimulus pairs constitute a potency equivalence function, which describes the shape of the relationship between equipotent positive and negative stimulus magnitudes.