People are notorious for not wanting to waste our time and effort — to the point that we’re willing to sink more of both into an endeavor we’re already on even if it is obviously futile. Our primate relatives seem to be the same.

Our reluctance to give something up after we’ve worked hard to get it, or otherwise invested a lot of time of effort in, is known as the “sunken cost” fallacy. In essence, the more effort you’ve put into something, the likelier you are to keep working on it even if you know it’s for naught.

It hails from our very distant past, in our ancestors and the ancestors of the human race. It’s a mechanism that makes sure our brains won’t give things up easily and instead wait for a return on investment — giving up too early might mean wasted energy, which could very well mean death in the wild. But there are many scenarios in modern times when the sunken cost fallacy is a net drain on our achievements and quality of life.

New research comes to help us understand the roots of the sunken cost fallacy, finding that two of our related species — capuchin monkeys and rhesus macaques — are also susceptible to this behavior.

Money business

“The epitome of the sunk cost is I’ve invested so much in this, I’m just going to keep going,” said Professor Sarah F. Brosnan from the Georgia State University (GSU), the paper’s senior author.

The team believes there are two factors that work together to generate the sunk-cost fallacy. The first is an evolutionary mechanism meant to help us balance costs and benefits. The second factor is uncertainty regarding the outcome: it might work, so why not keep at it?

They tested this hypothesis through a series of experiments with capuchin monkeys and rhesus macaques, finding that both are susceptible to the sunk cost fallacy, especially so when they’re uncertain about the outcome.

Housed at the GSU’s Language Research Center, the primates have both indoor and outdoor areas available to them, either for play or to take place in voluntary, non-invasive cognitive and behavioral research Brosnan says.

In the study 26 capuchin monkeys and 7 rhesus macaques played a simple video game. Through a joystick, they could move a cursor onto a target. If they successfully hovered it over the target as it moved, they would hear a sound and get a treat. If they failed in the task, they wouldn’t get a reward and the game would restart. After they got the hang of it, the team would test the primates on rounds of either 1, 3 or 7 seconds.

“Monkeys have really quick reaction times on these games,” said Brosnan, “so one second to them is actually a long time.”

Most rounds actually only lasted for 1 second, the team notes. From a purely practical point of view, this means that “if you didn’t get a reward after that, it was actually better to quit and start a new round”, according to Brosnan. That’s not what the animals did, however.

“They persisted 5 to 7 times longer than was optimal, and the longer they had already tried, the more likely they were to complete the entire task.”

Uncertainty was a powerful driver here, as the monkeys were less likely to continue the experiment if they got a signal that additional time and effort was required (though they wouldn’t always stop). They see this as an indication that the sunken cost fallacy is a product of evolution, and it’s deeply rooted in our developmental history (since these species are relatively distantly related to us). An animal’s ability to hunt, forage for food, or to wait for an appropriate social context would benefit from such a mechanism.

It also shows that it’s not a product of our higher mental abilities such as rationalization, from our concern to maintain our public image as someone reliable and capable, or anything similar. These factors likely help flesh the fallacy out, but our relatives can’t boast them to the same extent as we do.

Finally, the team notes that their findings show why tenacity isn’t always a virtue. Understanding the mechanisms that tug on our motivations from the shadows may then help us lead better, more fulfilling lives by focusing on what really matters to us.

“We’re predisposed to keep trying,” Brosnan said. “And when we find ourselves sticking with things, we should also be a little reflective. Do I have a good reason to keep trying? Or should I leave with no reward, because it will save me more in the long run? That’s really hard to do. But hopefully we can use our cognitive abilities to help us overcome the emotional heartache of occasional sunk costs.”

The paper “Capuchin and rhesus monkeys show sunk cost effects in a psychomotor task” has been published in the journal Scientific Reports.