Diamond, an evolutionary biologist, explores human history from the Stone Age hunter-gatherers to today's complex societies. His thesis focuses on environmental factors as the major influences on a society's development as opposed to the many racially-based theories of human history. He maintains that today's "less developed" societies are actually composed of smarter individuals because they have to grapple with daily life at a survival level. This book explores how the Eurasian content was the major winner because of its east-west orientation and width that allowed knowledge to pass more porously through different societies. North and South America, as well as Australia, had different challenges because of their north-south orientation and geographical features. Diamond also had some interesting comments on how today's food supply is based on 7 plants and 5 mammals that were domesticated thousands of years ago.