The Corners of My (Stone-Age) Mind

My first phone number was Prospect 67210. The quaint sound of that number is enough to tell you how long it has been bouncing around in my neurons. I also recall the street address that went with that phone number: 211 Elm Drive. I can vividly picture the grey Cape Cod house in my mind’s eye, and I believe I could even find my way around the neighborhood all these decades later.

I wonder why that would be. That chapter in my life is long gone, and it will never recur. I have never once actually used this information since I moved from my childhood home. What possible value could it have that I would still have it in my synapses? And why those particular details, when I have forgotten so much else?

Psychologists have spent a lot of time over the years describing what and how we remember, and there are volumes on how to improve memory. But little is known about the most basic question of all: Why remember? Why do we have memory at all? Purdue University psychologists James Nairne and Josefa Pandeirada decided to tackle this root question from a Darwinian perspective. They figured that memory, much like our kidneys and eyes and limbs, must have been shaped by eons of evolution. That is, it must have had some sort of survival value deep in the past. But why would nature have designed our “mnemonic organ” to work precisely the way it does? What’s the purpose of storing away the past?

The psychologists decided to explore these questions in the laboratory, starting with this premise: The only value of the past is in illuminating the present or predicting the future. It therefore makes sense to remember only those things that once helped solve “problems” related to the survival of the species: the location of food and water, signs of predators and potential mates, and so forth. It would also make sense to forget a lot of the rest, since the clutter of indiscriminate remembering would paralyze us.

To test this idea, the scientists had volunteers imagine spending a couple months alone in an unknown and uncivilized place, a grassland, without any useful tools for survival. Then they were given a list of words, which they were asked to rate for survival value. Because the words were randomly selected (stone, chair, meadow, and so forth), volunteers had to think a bit about whether each thing could conceivably have any usefulness: A chair might be a nice luxury, for example, but how might it be useful to a survivalist? How about a rock, or flowers?

The psychologists had other volunteers rate the same words for either pleasantness or for their relevance to moving abroad. Then they gave all the volunteers a surprise memory quiz, asking them simply to recall as many words from the list as they could. The results were memorable: Those who had imagined getting by in the wild remembered far more survival words, compared to the others’ recall of pleasant or moving-related words. These findings suggest that memory is indeed adaptive; that it has been “tuned” to information about evolutionary fitness.

Nairne and Pandeirada decided to look at these findings a different way. As described in the August issue of Current Directions in Psychological Science, they pitted survival memory against the best known tricks that memory researchers have for enhancing memory, in a head-to-head competition. This “who’s who” of memory devices includes forming a visual image of a word, creating an autobiographical memory related to a word, and simple effortful memorization. Again, they used a random list of words, and had volunteers use these various methods to process them. And again, simply thinking about words in terms of their survival relevance led to far greater recall than any of the other tried-and-true memory enhancement techniques.

So what does this say about how memory is organized in the brain? The scientists say it’s unlikely that the brain has a “survival module”; the concept of species survival is just too broad and amorphous. It’s more likely that evolution has engineered more finely tuned modules for recognition and storage of information—about predators, say, or poisons or nutrition.

Or safety and shelter, perhaps. Think about it: For a kid, what could be more important to survival than being able to find your way back home? It would make sense to burn those coordinates indelibly into the neurons. Which would explain why I could still reach home in an instant: Just dial Prospect 67210.

For more insights into the quirks of human nature, visit “We’re Only Human . . .” at www.psychologicalscience.org/onlyhuman. Selections from the weblog also appear in the magazine Scientific American Mind and at http://www.sciam.com/.