Learning not to learn: Nature versus nurture in silico

Animals are equipped with a rich innate repertoire of sensory, behavioral and motor skills, which allows them to interact with the world immediately after birth. At the same time, many behaviors are highly adaptive and can be tailored to specific environments by means of learning. In this work, we use mathematical analysis and the framework of meta-learning (or'learning to learn') to answer when it is beneficial to learn such an adaptive strategy and when to hard-code a heuristic behavior. We find that the interplay of ecological uncertainty, task complexity and the agents' lifetime has crucial effects on the meta-learned amortized Bayesian inference performed by an agent. There exist two regimes: One in which metalearning yields a learning algorithm that implements task-dependent informationintegration and a second regime in which meta-learning imprints a heuristic or'hard-coded' behavior. Further analysis reveals that nonadaptive behaviors are not only optimal for aspects of the environment that are stable across individuals, but also in situations where an adaptation to the environment would in fact be highly beneficial, but could not be done quickly enough to be exploited within the remaining lifetime. Hard-coded behaviors should hence not only be those that always work, but also those that are too complex to be learned within a reasonable time frame. The'nature versus nurture' debate (e.g., Mutti et al., 1996; Tabery, 2014) - the question which aspects of behavior are'hard-coded' by evolution, and which are learned from experience - is one of the oldest and most controversial debates in biology.