The transition from hunter-gatherer foraging to settled farming — occurring independently in at least seven regions across ten thousand years — that produced surplus food, population growth, cities, states, writing, and social hierarchy, and that Jared Diamond called 'the worst mistake in the history of the human race' even as it made civilization possible.
For 95% of human history, people hunted and gathered. Then, independently and in widely separated places, they started farming. This was not obviously a good idea — early farmers were shorter, sicker, and worked harder than their forager ancestors. But farming produced surpluses, surpluses enabled populations to grow, growing populations made going back impossible, and eventually farming enabled cities, states, writing, armies, and everything we call civilization. Whether this was a disaster or a triumph — or both simultaneously — is one of the most productive questions in human history.