Our early hunter-gatherer ancestors lived in isolated territories. One might think that, over time, their expanding populations would have exhausted resources in their territories and led them to develop agriculture, but the archaeological evidence does not support this view. Instead, hunter-gatherers practiced birth control by delaying the weaning of their children or, during the worst of times, killing the children or migrating elsewhere.

Today there is ample evidence of farming societies encroaching on the territories of hunter-gatherers and compelling them to switch to farming. There are many cases where traditional hunting and gathering grounds have been wiped out by deforestation for lumber, agriculture, or access to mineral resources. Yet these circumstances did not apply when agriculture first came into being.

Life also seems to have been a lot more leisurely for small groups of hunter-gatherers than for farmers , who had to work long hours to gain the same nutritional benefi ts. So making the transition to agriculture did not happen because it was less work or more fun. When resources became limited in their territories, hunter-gatherers just moved to more suitable environments, something quite possible when populations were small. There was no apparent time or energy benefi t that would have encouraged them to switch to agriculture. What triggered the shift?