before we started cultivating wheat, humans were very cooperative. once you had wheat, you had people who didn't have to labor directly to provide themselves with food. then you get job specialization, landlords, and populations that were so large they required a permanent commitment to agriculture or else there'd be mass starvation, and well, look where that got us. in fact, the etymology of the word "greed" comes from the persian word "wheat." source for that last part: my ass.