Accuracy or Self Enhancement: The Evolutionary Pressures on Autobiographical Memory

Surely autobiographical memory needs to be somewhat accurate to help us survive? Nevertheless changing stories to self-enhance may have been another evolutionary pressure.

In conversation with the memory psychologist Hartmut Blank, we were discussing that surely there was an evolutionary pressure to make memory accurate. Surely memory has to be somewhat accurate. I agreed that very least there is an evolutionary pressure to be accurate in remembering goal-important things: for example where food was found previously. There is also an evolutionary pressure to perhaps optimize the brain system for important recent events, and perhaps to deemphasize the use of mental resources for very old memories. The evolutionary gain to use brain resources to remember where food was 30 years ago is much less important than remembering how things have gone in the last 5 years.

The constraints on the evolution of the memory system are many. There are constraints in terms of just energy and resources. Resources such as proteins, fats, and glucose were limited during the evolution of humans, so the memory system was under high pressure to be just good enough for survival and cultural thriving, but there was little advantage in using more resources beyond that to build a memory system that was perfect.

The other major constraint, of course, is infant mortality in a species with large heads and pelvic adaptations for upright walking. Human head size seems to have led to a tragic trade-off between mother and infant mortality on the one hand, and head size and therefore neural capacity on the other. In other words, there is a strong evolutionary pressure to keep the neural networks involved in memory small and efficient. Thus what we have now are memory systems good enough to eat, reproduce, and pass on human culture. Accuracy is important in some of these domains, but not all. Being able to use the same neurons repeatedly for newer memories is a great solution to this dilemma. Overwriting old memories with modifications might be a side effect of these evolutionary efficiency drives. Memory malleability may be part of the efficient incorporating of new information into older memories.

So far we have talked about memory in general—where to find food, how to do things to survive, and so on—but now let us focus in on autobiographical memory. And by this, I mean the type of memory that we tell in stories to others in our tribe, and it often involves a recurring relation to self (e.g., “I did this, then I saw that”). This particular type of memory has some evolutionary pressure for accuracy. If our tribe member accurately relays to us about a story relating to food, predators, or other tribes, there is some pressure that that storytelling to have enough accuracy in some of the key details. Nevertheless, there is another evolutionary pressure—that which benefits the individual, so we may have also evolved to self-enhance these autobiographical memories as well. Changing our stories to elicit admiration, sympathy, or protection may have been a real evolutionary pressure ever since language evolved in humans. Whether those manipulations of memory, these self-enhancements, are true or not may not always be even known or noticed by the individual enhancing their story. In fact, not knowingly lying may be an advantage, because the falsities that develop in autobiographical memory are far more likely to be believed by others if they are believed by the teller of the story.

This evolutionary advantage of sometimes self-enhancing autobiographical memory may explain how false memories arise over years after a dispute between people (whether that be family disputes or divorces). If there is a motive set up to misremember, human memory systems may self-enhance and change the narrative over time in ways that evolved more for social-survival reasons, as opposed to accuracy pressures. We are excruciatingly social animals to a fault, and autobiographical memory has a very social origin. Story telling was likely an integral part of gaining and maintaining social esteem in the very group one was completely dependent on for survival. It is hardly surprising that human autobiographical memory changes over time to create a narrative that promotes liking and/or denigrates ones social opponents or competitors, after hundreds of thousands of years of brutal social survival among tribal hunter-gatherer apes.

Perhaps, then, it is hardly surprising that we will sometimes see legal cases where some rivalry of dispute occurred between people, and before that time no claims of illegality existed. Often there is a long time after the dispute when no memories or claims of illegality occur. Then, over a period of many years, one side of the dispute develops autobiographical memories, gradually over time, that have evolved over time with every new telling, that now contain falsities.

So yes, there are some evolutionary pressures for memory to be accurate. But there are other evolutionary pressures that seek to limit head size, resource use of glucose and other nutrients, and those pressures constrain all the various types of the memory systems we have. In these systems, there is a prioritization of the recent, the important for survival, with some pressure to reuse neurons in memory networks for new events or learning. Specifically in the case of autobiographical memory, there is the added evolutionary pressure of the self-enhancement of stories within the context of the hyper-social and survival-dependant tribes our species evolved in. There is likely even an advantage to believing self-enhancing distortions if they elicited support, protection, or if they successfully defeated perceived social competitors or adversaries.