The sunk cost effect across species: A review of persistence in a course of action due to prior investment
Sunk-cost bias is not just a human mistake—animals also persist after prior investment, so BCBAs should plan for it in any long program.
01Research in Context
What this study did
Magalhães et al. (2016) gathered every sunk-cost experiment done with animals. They looked at pigeons, rats, and other species. The goal was to see if animals, like people, keep working after they have already paid a cost.
The paper is a narrative review, not a new experiment. The authors compared procedures and results across labs. They asked whether animals show the same "throw good money after bad" pattern.
What they found
Animals do persist after an initial cost. Birds kept pecking even when food no longer paid off. Rats kept pressing a lever even when a better option sat next to them.
The review says this looks like the sunk-cost fallacy seen in humans. The effect is not just a human quirk; it crosses species.
How this fits with other research
Avila et al. (2013) showed that humans fall into the sunk-cost trap only when the cost difference is tiny. When the gap is large, people switch. Magalhães et al. fold this human data into their cross-species story, making the review a sequel rather than a clash.
Vasconcelos et al. (2007) failed to find a "work ethic" effect in pigeons; birds did not prefer stimuli that took more work to earn. That null result might seem to fight the idea that animals value prior effort. The review, however, treats sunk cost and work ethic as separate phenomena, so the papers coexist without contradiction.
Doughty et al. (2010) found that pigeons and humans both shift choices when token exchange is delayed. The review cites such cross-species parallels to argue that basic choice mechanisms are shared, even if risky delay differs from sunk cost.
Why it matters
If animals and humans both stick with a losing plan, the mechanism is likely evolution-old, not a fancy human bias. For BCBAs this means persistence can be triggered by prior reinforcement even when the payoff stops. Watch for this in token boards, response chains, or long tasks. Build easy exit ramps and teach clients to cut losses early. Data paths that keep climbing despite zero gains may be sunk-cost behavior, not commitment to mastery.
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Put a brief "quit rule" in the program: if no reinforcement occurs for three consecutive minutes, prompt a switch to a backup task.
02At a glance
03Original abstract
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.
Journal of the Experimental Analysis of Behavior, 2016 · doi:10.1002/jeab.202