The evolutionary origins of memory use in navigation

Many organisms are able to cope with environmental variations through an array of innate behaviors. When environments change too quickly for evolutionary processes, or when the variation is more unique to a particular place, time, or individual organism's experiences, innate responses may need to be augmented by more flexible responses that use individual life experience. In such situations, memory becomes necessary. Generally, memory refers to the stored record of experience, and is of great interest across many disciplines.;I focus this study on the question of how evolution produces complex memory structures, by examining the interaction of environment and memory during evolution in an environment where navigation is an important behavior. Digital organisms evolve to navigate within their environments, based on different sensory cues. The different environments present differing problems that require different uses of memory.;The simplest environment is an idealized version of the chemical attractant gradients in the environments of bacteria such as Escherichia coli. These experiments demonstrated the evolution of both a chemotaxis-like response (i.e., organisms evolved to move up the virtual gradient and approach the highest concentration), and a rudimentary one-timestep memory.;Inspired by maze-learning experiments with bees, in the next suite of experiments, the digital organisms evolved in environments with "paths," formed by sensory cues in the environment. I used several different types of paths, and each path type placed different demands for memory use on the evolving organisms. The results of the first group of path-following experiments demonstrated the evolution of "reflex" actions, where organisms responded in a fixed way, but differentially, to the environmental cues. For the second suite of experiments, I focused on evolving a one-bit individual memory. One experiment evolved a one-bit life-long memory, i.e., remembering a binary decision, in the form of which direction to turn in the current environment. This meant that an organism needed to store and refer to a single individual experience in future decision-making, but the content of the information did not change during the individual's lifetime. In the next set of experiments, I focused on evolving a volatile, "short-term" individual memory. In these environments, new experiences that influenced future decisions happened at unpredictable times, requiring the the stored experiences to be updated frequently.;The results of the experiments demonstrate that robust, flexible behavior can evolve even in simple environments. Organisms that evolved in each of the experimental environments exhibited clever and flexible behavior that demonstrated simple behavioral intelligence, revealing capacities such as gathering and differential use of environmental information, and the ability to use prior individual experience to guide future actions.