The Neolithic demographic transition was a period of rapid population growth following the adoption of agriculture by prehistoric societies. It was a demographic transition caused by an abrupt increase in birth rates due to the increased food supply and decreased mobility of farmers compared to foragers. Eventually the mortality rate in farming societies also increased to the point where the population stabilised again, possibly because settling down in one place, in close proximity to animals, encouraged the spread of zoonotic and waterborne diseases. The transition is estimated to have taken about a thousand years on average, although the onset and duration of the transition varied widely in the different parts of the world.