All grass based crops encouraged group cooperation. Plants like potatoes remain safe in the ground until you need them. But all cereal crops require harvesting at a specific time. You can’t just harvest enough wheat as you need it. This means you inevitably have to have a stockpile of grain to get through the year. And a stockpile of already harvested and prepared grain makes you an instant target for raids by opposing groups.

Cereal crops of all forms necessitate cooperation.