Cultural Evolution with Sparse Testimony: when does the Cultural Ratchet Slip?

Humans have accumulated a wealth of knowledge over the course of many generations, implementing a kind of “cultural ratchet”. Past work has used models and experiments in the iterated learning paradigm to understand how knowledge is acquired and changed over generations. However, this work has assumed that learners receive extremely rich testimony from their teacher: the teacher's entire posterior distribution over possible states of the world. We relax this assumption and show that much sparser testimony may still be sufficient for learners to improve over time, although with limits on the concepts that can be learned. We experimentally demonstrate this result by running an iterated learning experiment based on a classic category learning task.