Lectures are such an effective teaching method because they exploit evolved human psychology to improve learning.

Lectures are probably the best teaching method for many students in many circumstances; especially for communicating conceptual knowledge, and where there is a significant knowledge gap between lecturer and audience. However, the lack of a convincing rationale has been a factor in under-estimating the importance of lectures, and there are many who advocate their replacement with written communications or electronic media. I suggest that lectures are so effective because they exploit the spontaneous human aptitude for learning from spoken (rather than written) information. Literacy is a recent cultural artefact, and for most of their evolutionary history humans communicated by direct speech. By contrast with speech, all communication technologies--whether reading a book or a computer monitor--are artificial and unnatural. Furthermore, learning is easier during formal, quiet, real-time social events. The structure of a lecture artificially manipulates human psychology to increase vigilance, focus attention, and generate authority for the lecturer--all of which make communications more memorable for the student. Instead of trying to phase-out lectures, we should strive to make them better by understanding that lectures are essentially formal, spoken, social events.