From Hunting – Gathering to Growing Food — Social Science STD 6 — Question

The climate of the world was changing and so were plants that people used as food.
People probably noticed several things:

1. Where edible plants were found.
2. How seeds broke off stalks.
3. Fell on the ground and new plants sprouted from them, and so on.

Perhaps they started looking after plants-protecting them from birds and animals so that they could grow and seeds ripen.