It was May 27, 2017—another late night for Brian Sweis. The 26-year-old MD/PhD neuroscience student had been running lines of code and analyses on tens of thousands of rows of data, dating back to experiments conducted in 2012. The goal: to better understand “sunk cost,” the idea that the more you invest in something, the harder it becomes to abandon it, even in cases when it is in your best interest to do so. A long-term relationship gone awry, for example, is harder to leave than a short-term one. Even when inadvertently choosing a longer line at the grocery store, people struggle to back out of the decision and move into a shorter one.

Sweis and his colleagues at the University of Minnesota were specifically interested in how sunk cost impacts decision-making—not just in humans, but in rats and mice, too. Alex Kacelnik, a behavioral ecologist at the University of Oxford who was not involved in the study, puts it this way: “If you find that one species makes a systematically bad choice, you can argue it’s an accident of history. But if you find a very different species does the same thing—then, come on, there must be some reason why evolution doesn’t eliminate this form of behavior.”

Sweis and his team decided to investigate the phenomenon in different species. Some of their most recent findings, published Thursday in Science, show rats, mice and humans all exhibit sunk cost behavior. Their analyses also suggest both rodents and humans have separate decision-making processes that are not all susceptible to sunk cost. The time one spends making a decision, whether or not to leave that relationship or grocery line, is not considered part of the sunk cost; only time invested after the decision is made is taken into account. When Sweis made this realization, he e-mailed his advisor late that night in May, calling the findings “flipping huge.”

As the team considered how best to analyze their results and test similar decisions in humans, studies on sunk cost landed on the front pages of some of the field’s most prestigious journals. Some found rodents are susceptible to this phenomenon; others found they are not. Research in other species, including in birds, also yielded mixed results. For the Minnesota team , the key was not only to test sunk cost in rodents but to gauge how these decisions played out in humans as well. “The goal of the field is ultimately to improve human behavior, so being able to translate rodent findings across to humans is sort of a gold standard,” says Shelly Flagel, a behavioral neuroscientist at the University of Michigan who was not involved in the study.

Flagel and others find the results exciting. But they warn against drawing sweeping conclusions from the study. “There are always going to be caveats, especially when drawing parallels between rodent and human behavior,” Flagel says. One of the central limitations of this research is that it doesn’t look at consistent behaviors across humans, mice and rats. Although foraging for online information and food might be related activities, they are distinct—making the translation from rodent to human less certain. There is also the gender component: the mice studied were all male whereas females made up a majority of participants in the human study.

Read the full article at Scientific American.