According to Diamond, the ancestors of human beings broke off as a separate lineage from other animals about seven million years ago in Africa. Human ancestors began walking upright around four million years ago, and they moved to Eurasia around one or two million years ago. Sometime between 100,000 and 50,000 years ago, not long after human fossils began to resemble modern homo sapiens, our race created an explosion of new technological and artistic innovations that far surpassed anything previously created. Archaeologists call this period the Great Leap Forward.

Shortly after the Great Leap Forward, between 50,000 and 35,000 years ago, the human race expanded its territory. Although human ancestors had remained in Africa and Eurasia for millions of years, people now moved outward to Australia, the South Pacific, and the coldest northern regions of Eurasia. The precise dates of human arrival in the Americas are harder to determine, but the colonization happened at least 12,000 or 13,000 years ago. Diamond thinks it is remarkable that human beings moved into all habitable areas of the globe in a few tens of thousands of years without the benefit of modern technology.

Diamond begins his consideration of the fates of human societies around 11,000 BCE, or 13,000 years ago, because during this period all the habitable continents were populated with hunter-gatherers, and no society had advanced technologically to become farmers or city dwellers. Diamond asks whether a modern archaeologist, transported back 13,000 years, could determine which continent’s people would have the best chances for developing advanced technologies. Considering each continent in turn, he lists the qualities one might consider to be advantages.

In 11,000 BCE, Africa had been populated for the longest time, which would have allowed its people to develop the most expansive knowledge of their landscape and environment. Africa’s people were also more genetically diverse than were the people of other continents, which suggests they might have had a greater range of genetic adaptability.

The Americas had been populated the shortest length of time. The Americas, however, had more space and environmental diversity than Africa did. Taken together, the Americas were also larger than any continent except Eurasia. Diamond reasons that both of these factors may have given early Americans an advantage.

Eurasians had the largest continent and the second largest genetic diversity of all the continents. Eurasia was the second earliest continent to become populated. Human populations on that continent were already creating complex art and tools. Diamond hypothesizes that any of these factors may already have been giving early Eurasians a head start.

Finally, Diamond considers Australians and New Guineans. Their continent was the smallest and, in some ways, the least accessible continent in the world. However, Australians and New Guineans had the earliest boats, and the archaeological record shows Australia’s people had developed a level of artistic achievement similar to that of Europe at the time.

After this review, Diamond concludes that all the continents appeared to have some advantages over all the others. He feels that a modern archaeologist transported back in time to 11,000 BCE could not, without further information, predict which continent’s population would become most successful.