The sunk cost effect across species: A review of persistence in a course of action due to prior investment.

The sunk cost effect is the bias or tendency to persist in a course of action due to prior investments of effort, money or time. At the time of the only review on the sunk cost effect across species (Arkes & Ayton, 1999), research with nonhuman animals had been ecological in its nature, and the findings about the effect of past investments on current choice were inconclusive. However, in the last decade a new line of experimental laboratory-based research has emerged with the promise of revolutionizing the way we approach the study of the sunk cost effect in nonhumans. In the present review we challenge Arkes and Ayton's conclusion that the sunk cost effect is exclusive to humans, and describe evidence for the sunk cost effect in nonhuman animals. By doing so, we also challenge the current explanations for the sunk cost effect in humans, as they are not applicable to nonhumans. We argue that a unified theory is called for, because different independent variables, in particular, investment amount, have the same influence on the sunk cost effect across species. Finally, we suggest possible psychological mechanisms shared across different species, contrast and depreciation, that could explain the sunk cost effect.