In prehistoric times, agriculture developed spontaneously in several different parts of the world; then it spread outward from there to many other regions. The places that developed agriculture are not the most fertile; indeed, some extremely fertile areas like California never encountered farming or herding until after Europe’s colonialist period began.

After noting these facts, Diamond asks a series of questions: Why did farming and herding techniques arise at different times in different places? Why did they take longer to spread to some areas than to others? Why did the shift from hunter-gatherer societies to agricultural societies sometimes involve the violent replacement of one group of people by another?

Diamond explains that archaeologists can discover when and where agriculture arose by dating evidence of domesticated plants and animals and then comparing this evidence to the archaeological record of the domesticated species’ wild cousins. He explains that this process yields plausible but inexact information, which is particularly complicated when people appear to have domesticated the same species more than once in different places.

There are five places where people certainly invented agriculture independently without first having encountered farmers or herders from elsewhere: Southwest Asia’s Fertile Crescent, China, Mexico, the South American Andes, and Eastern North America. In four additional places, agriculture may have arisen independently, but the archaeological record is uncertain. These places are the African Sahel, West Africa, Ethiopia, and New Guinea. With his discussion of these places, Diamond provides lists (see table 5.1 in the book) of the early sets of plants and animals domesticated in each area.

Next Diamond examines evidence from archaeological sites, including Egypt, Western Europe, and the Indus Valley, where food production techniques appear to have been imported and where people also domesticated new plants. In Egypt, hunter-gatherers apparently adopted farming and herding gradually, phasing out their use of wild foods over time. Diamond believes this is evidence that the local population adopted farming techniques from their neighbors rather than inventing it on their own. He states that this kind of shift happened in several other archaeological sites around the world at various times.

Western Europe seems to have adopted agriculture in a different way than Egypt did. Although the archaeological evidence for Europe is incomplete, it seems to suggest a sudden shift from wild foods to an entirely new diet. Diamond thinks this means the land was conquered by invaders from southwest Asia who did not know much about Europe’s wild plant species. He claims that recorded history shows numerous examples of similar land takeovers by invading food-producing societies.

Diamond has now explained where agriculture arose and shown that it spread to new places in different ways. The next chapter will answer his questions about why the techniques arose and spread as they did.