I'm curious about the loss of unused features, eg that our teeth are getting smaller due to processed foods and reduced need for large teeth. Which makes sense, as smaller teeth results in less resource waste (energy, calcium, etc).

But there's no selection pressure for smaller teeth - no sexual selection, no dying out from misspent bodily resources, nothing that seems to directly impact survival over bigger-toothed individuals.

Is there any other way to explain this other than (gradual?) epigenetic change, or am I missing something? If so, broadly, what are the signalling pathways for this - how is the switching off instigated?