They're edible with your teeth when young/fresh....
The quality of grains that made them staples is that they could be dried/hardened. That way they keep all winter, can be traded, etc.
For an everyday example, think of beans. We sometimes eat them fresh/soft as vegetables (green beans or edamame). More often they're dried, stored, traded on commodity markets and then re-softened to be eaten as soy cheese or chili con carne.
"They're edible with your teeth when young/fresh..."
No, I do mean the ripe ones. I am a bit into survival food and know the differences - but as I said, only of the grains I tried so far. I could chew them with no big problems.
The quality of grains that made them staples is that they could be dried/hardened. That way they keep all winter, can be traded, etc.
For an everyday example, think of beans. We sometimes eat them fresh/soft as vegetables (green beans or edamame). More often they're dried, stored, traded on commodity markets and then re-softened to be eaten as soy cheese or chili con carne.