Agriculture. When you plant a seed you have to protect it. You have to nurture it and when its time to harvest you have to make a claim to own it against people gathering free stuff. Pretty soon you have to have an army and priests and civilisation - all these people get power so that the seed planters, end up chained to a mill to grind corn for bread whilst the elites eat beef fed on the grain you are growing whilst all you get is bread. This is the start of the class system religion and monarchy, where a handful enjoy the benefits and the rest are slaves to the system. This is pretty much what happened in several places all over the world whilst the tradition of hunting and gathering was pushed to the margins. Pretty soon we were all getting diseases from foods we are ill desgined by evoution to thrive on. Oh um
Contraceptives.
crystal meth