The Prisoners Dilemma, Memory, and the Early Evolution of Intelligence

Memory is an essential component of intelligence as it enables an individual to make informed decisions based on past experiences. In the context of biological systems, however, what selective conditions promote the evolution of memory? Given that reliable memory is likely to be associated with costs, how much is it actually worth in different contexts? We use a genetic algorithm to measure the evolutionary importance of memory in the context of the Iterated Prisoners Dilemma, a game in which players receive a short-term gain for defection, but may obtain greater long- term benefits with cooperation. However, cooperation requires trust; cooperating when an opponent defects is the worst possible outcome. Memory allows a player to recall an opponents previous actions to determine how trustworthy that opponent is. While a player can earn a high payout by defecting, it will likely lose the trust of an opponent with memory, yielding a lower long-term payout. We determined the value of memory in the Iterated Prisoners Dilemma under various conditions. When memory is costly, players reduce their available memory and use short-term greedy strategies, such as Always Defect. Alternatively, when memory is inexpensive, players use well-known cooperative strategies, such as Tit-for-Tat. Our findings indicate that organisms playing against a static opponent evolve memory as expected. However, memory is much more challenging to evolve in coevolutionary scenarios where its value is uneven.