How does stochasticity in learning impact the accumulation of knowledge and the evolution of learning?

Learning behaviors are crucial for humans and other animals to adapt to their environment by acquiring and using knowledge that enhances survival and reproduction. In particular, some learning behaviors allow populations to accumulate knowledge across generations (‘cumulative knowledge’ or ‘cumulative culture’). Here, we examine how individual stochasticity in the production and social acquisition of knowledge influences the evolution of learning behaviors and cumulative knowledge. Using a mathematical model where learning is a stochastic process, we show that stochasticity in learning enhances cumulative knowledge by generating variability in knowledge levels: individuals who acquire more knowledge by chance are more likely to survive and reproduce, and therefore more likely to transmit their knowledge to the next generation. As knowledge accumulates, social learning exemplars tend to possess more of it, favoring greater investment of time in social learning. Because social learning provides access to substantial amounts of knowledge, selection favors the evolution of more effective learning, at the expense of a fecundity cost. Moreover, when knowledge enhances fecundity but not survival, we find that selection favors learning from parents rather than unrelated adults. This is because parenthood signals reproductive success and, therefore, a higher likelihood of possessing fecundity-enhancing knowledge, unlike random adults.