This article introduces the concept of "natural pedagogy" (NP) as a tool for envisioning and enacting second language learning and teaching. Currently popular in the social and cognitive sciences, NP theory holds that much adaptive human behavior is too complex and nontransparent to learn via observation, imitation, and trial-and-error alone: Something extra is needed. NP employs humans' remarkable "hyperprosocial" capacities/tools for interaction (e.g., gesture, gaze, facial expression, body movement, language) to effect "teaching-based learning." NP's appearance in the hominin lineage likely predated humans; it is probably therefore the original form of teaching-based learning. A much more recent invention--the classroom--is often portrayed as separated from the rest of the world in order to enable teaching-based learning. Yet the interactional tools of NP occur pervasively in classrooms as well, making classrooms in this sense substantially continuous with the rest of the world. In both cases, according to the argument developed here, our evolved communicative toolkit underlies teaching-based learning. This article is primarily conceptual in nature, representing a new departure in the TESOL field.