Chances are agriculture began slowly as foragers started encouraging wild crops. As their efforts paid off, their populations increased. Eventually these forager/farmers would get trapped into agriculture, their populations having grown too large to be supported by the environment.
I was under the impression that slash-and-burn nomadic farming techniques pre-dated sedentary agricultural settlements. There are also various nomadic groups that forage for plant material, but bring herds of food animals with them. It seems unlikely to me that this was a historic starting point though.
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