The softer foods reduced the need for strong mandibular muscles.
Explanation:
Remember that the body responds to the necessities that we have, for example our ancestors needed bigger teeth and greater mandibular muscles because they had to eat mostly raw meat and uncooked vegetables that they would find on the fields, when agriculture and consumption of softer foods came along the human morphology changes because we no longer needed those strong muscles nor big mouths so our faces became more finese, and our mandibular muscles strated to get shorter and weaker making more rounded faces.
The morphologic changes to the modern human faces as well as mandibles and the teeth after the shift of the agricultural and consumption of the softer food were having a high and vertical forehead, tall and round skull, small face with a small teeth and chin.
