Hunter-gatherer populations were much less dense than later agriculturalists. The variety of their food supply protected them from crop failures and their sparseness reduced the spread of infectious diseases. Hunter-gatherers were healthier and worked less than early agriculturalists. Why didn't their numbers increase up to the same level of Malthusian misery? Their numbers may have been limited by violence between groups. Agriculture is more work intense and offers a less varied diet. Populations seem to grow rapidly and then die out suddenly. Populations are subject to climatic- or disease-caused crop failure. But farming allows individuals to produce a surplus of food that can then be stolen by warrior tribes or military castes. The surplus allows for population growth, cities and stratified societies. The death rate, until perhaps the 1700s in Europe, is enormously high: only approximately a third of women survive to the end of their reproductive period. At this death rate, surviving women who are able to reproduce must have more than six children on average or the society goes extinct. All the great religions and cultures develop in this long period and all stress the requirement for high reproductive rates: "Be fruitful and multiply."