My hypothesis: We domesticated animals starting with sheep and goats. The pastoral lifestyle allowed a population explosion leading to overgrazing. Then seasonal rains swept topsoil into the river valleys on a yearly basis. What could be easier? The floods fertilized and irrigated the valleys. Bugs and weeds were wiped out. Poke a hole in the silt and plant your grain. Voila! Bread, beer, and the easy life. Hence the early civilizations of Mesopotamia, the Indus, China, etc.
"Poke a hole in the silt and plant your grain..."
Must resist... too early too be nasty!