In every part of the world where there is sufficient evidence, archaeologists find evidence that the population density has increased along with the emergence of food production. Poster dog and she lived happily ever after. Where is cause and effect? This is a long controversial question like the “pre-existing egg or previous chicken” question: is the increase in human population density forcing people to turn to food production, or thanks to Food production that one can increase population density? In principle, one might argue that the causal chain operates in both directions.