Legacy of the Stone-Age Mind

Imagine you are stranded in the grasslands of a foreign land, with nothing but the clothes on your back.  In order to survive, you’ll need to find steady supplies of food and water and protect yourself from predators.

You now share the mindset of our savannah-wandering ancestors, and, says one researcher, being in that mindset can improve your memory.

James Nairne, a psychology professor who studies the evolution of memory at Purdue University in West Lafayette, Indiana, has found that people better remember items from a list when they put themselves in the place of prehistoric humans, and imagine how those items might help them survive.

Human memory has evolved, Nairne suggests, so that thinking of something in terms of its fitness-relevance — how it could help us survive and reproduce in our ancestral environment — makes us more likely to remember it.

“Getting people to think about survival works [to improve memory] really well, presumably because that’s why our memory systems developed in the first place,” Nairne says.

Scientists agree that mental traits, like physical ones, are shaped by natural selection. Evolutionary psychologists investigate how the selection pressures our distant ancestors might have faced shaped our cognitive functions.

Most evolutionary psychology research has focused on stimuli rather than processes, what we think about rather than how we think about it.  But Nairne’s work centers on how people remember when their survival is at stake. He looks at how situation influences memory — specifically, a situation our ancestors likely faced during the Pleistocene Era, which ended 10,000 years ago, when most scientists think our modern cognitive traits developed.

Nairne asked one group of participants to put themselves in the footprints of early humans: You are stranded in the grasslands of a foreign land… He then asked them to rate how relevant each word in a list was to their survival.  Some words (“bear,” “tree”) fit with the wilderness survival scenario; others (“truck,” “screwdriver”) didn’t.

Participants in other groups saw the same words, but were asked to think about them in ways that psychologists have previously shown improve memory: thinking about how pleasant the words are, for example, or visualizing them.

Nairne found that considering the fitness-relevance of the words, more than any other scenario, improved participants’ performance on a surprise memory test.

Henry Roediger III, who studies memory at Washington University in St. Louis, Missouri, was impressed by the result.  “[Nairne] picked all the tasks that have been shown to be very good for memory, then showed his particular task was better than the best task that had been studied over the past thirty years,” Roediger says.

Just how fitness-relevance boosts memory is still uncertain. But Daniel Schacter, a memory researcher at Harvard University, says that while the mechanism is a mystery, the effect is real.

“We don’t really know the exact underlying basis,” Schacter says, “but whatever it is, thinking about survival engages the processes that … push memory in a positive direction.”

Roediger wondered if a modern survival scenario would have the same effect, or if, as Nairne hypothesized, fitness-relevance was specific to the savannah. Roediger asked participants to rate the relevance of words in a survival scenario located either in the grasslands or in a modern city, figuring a city scenario would facilitate memory more than a wilderness one, since “familiar things are generally easier to remember than unfamiliar things.”

“I was really surprised when we got the opposite effect,” he recalls — participants remembered more words when they thought about surviving in the grasslands than in an urban environment.

Nairne, too, is testing the limits of the fitness-relevance memory boost. He has found that participants remember things better when they imagine hunting or scavenging for food out of necessity than when they imagine hunting for sport or joining a recreational scavenger hunt. It seems that improved memory in fitness-relevant situations is tied not just to the kinds of tasks required of our distant ancestors, but to how important those tasks were to their survival.

Although there are some promising results, evolutionary psychology is a contentious discipline.  While Nairne’s work steers clear of making often-contested evolutionary claims based on certain stimuli, like an innate fear of spiders, there are still methodological obstacles.

“With psychological traits, there’s no fossil record,” says Lawrence Shapiro, a philosophy professor at the University of Wisconsin, Madison, who writes about evolutionary psychology. Without a definitive record of our ancestral psychology, “it’s difficult to determine whether a psychological trait is really an [evolutionary] adaptation.”

“Evolution of memory is a very tough issue to get at directly,” acknowledges Schacter. But, he adds, “if you don’t try to get at the topic, you’re probably not going to make much progress at all.”

Even if the particular evolutionary pressures that gave rise to fitness-relevance aren’t clear, Nairne hopes that elucidating the origins of memory will help us understand its current function.

“We now know that if you get people to think about how something relates to a survival situation, they will remember it better than [if you use] virtually all known techniques,” he says. “Whether that’s due to survival or something else, that’s an important thing to know.”