From 10,000 years ago, until 500 years ago, humanity was divided by geography. We lived in four separate world zones. These four different parts of the world were cut off from each other. The four zones each covered huge regions of the world. Humans living within each zone connected with each other, but almost never connected with humans in the other three zones. The four world zones were:

• Afro-Eurasia (Africa, Europe, and Asia)
• The Americas (North and South America)
• Australasia (Australia, New Guinea, and surrounding islands)
• The Pacific (Islands of the Pacific Ocean)

Why were there four world zones before 1500 CE?

By 10,000 years ago, humans had migrated to most of the land areas on Earth. The expansion of our species involved developing a lot of new technologies to deal with extreme heat and cold, to gather and process foods native to those regions, and to cross jungles, mountains, and deserts. Humans were now spread across huge expanses of the planet, and they lived in environments that differed widely. As a result, differences in how human communities lived emerged. Two big changes divided the world into four zones, each separated from the others.

The first was an environmental change. As the last big ice age came to an end, water levels rose. As the oceans flooded the coast, the land bridge between the Americas and Afro-Eurasia (Africa, Asia, and Europe) disappeared. Sea rise also flooded much of the land that once connected Southeast Asia and the islands of Australasia.

The second change had to do with human innovation. People in Southeast Asia developed the technology to sail into the vast Pacific Ocean. Learning to live on islands and travel the open ocean by ship, they migrated further and further across the vast Pacific Ocean, gradually separating from the peoples of Afro-Eurasia. Meanwhile, people who migrated to Australasia found quite different environments from others and had to develop new technologies to deal with them.

Were the four world zones really separate?

Some historians question whether there really were four different world zones. These historians argue that there is plenty of evidence of some contact between the zones. For example, Polynesian sailors of the Pacific probably did trade to some degree with people living on all three of the big landmasses—the Americas, Afro-Eurasia, and Australasia. Similarly, we know that the Vikings and maybe other Afro-Eurasians visited and sometimes briefly settled in the Americas before 500 years ago.

Other scholars ask whether we should really think of each of these four world zones as internally unified. Afro-Eurasia is a huge landmass, making up about 80% of the world’s habitable land. People in southern Africa during this period were hardly connected to people in Siberia or Britain. Similarly, societies living on islands across the vast Pacific were often quite different from each other, though connected through long chains of ocean voyages. And people living in the Andes mountains of South America probably didn’t know about people living in the Arctic Circle of North America.

Still, the differences between the four zones were generally more significant than differences between communities within each zone.

How were the four world zones different?

"What do the four world zones tell us about increasing complexity?"

Because Afro-Eurasia was a huge, connected landmass, technologies and species of plants and animals could spread across vast distances. Useful animals (like horses) and grains (like wheat and rice) were adopted by many different cultures, helping populations increase and large cities rise. Metalworking, especially with iron, spread to many societies in Afro-Eurasia, while writing became quite common. Because so many people and animals lived closely together in big cities and traded with people in other cities, diseases like smallpox and plague sometimes swept across huge areas, killing millions of people but also eventually giving populations in Afro-Eurasia some immunity.

The Americas were also very large and held diverse environments. Societies there had plants and animals in common as well, including population-sustaining crops like maize (corn) and potatoes, and some domesticated animals like llamas, alpacas, turkeys, and dogs. As a result, some very large societies emerged. But the geography of the Americas and the absence of pack animals like horses and camels made long-distance trade more difficult. There were still plenty of connections linking societies here, but in general, smaller populations and diverse environments meant that some innovations, in particular iron technology, didn’t emerge here.

Australasia includes some large islands and a big continent—Australia. But much of the land is desert or jungle. The people there had fewer domesticable plants and animals. Some, in New Guinea, for example, figured out how to farm those plants, but lots of people continued to forage instead. Populations remained relatively low, but they also suffered from fewer big disease outbreaks.

Finally, the Pacific, the world’s largest ocean, is dotted with archipelagos and individual islands. Probably the most important technology for people in the Pacific was their incredible sailing knowledge and ships, which allowed them to connect their island homes. Pacific peoples had some domesticated animals and plants they had either brought with them or found, including pigs, taro, and breadfruit. But many of their island homes were quite ecologically fragile, which meant they had to be very careful when starting farms or introducing animals that might destroy the land. Their societies were mostly quite small and, because they were separated by distance, disease didn’t spread fast between them.

Increasing complexity

Columbian Exchange: The transfer of plants, animals, people, ideas, and diseases between the Americas and the rest of the world after 1492

What do the four world zones tell us about one of the main ideas of Big History— that of increasing complexity?

Well, first, the four world zones would never have emerged as distinct human regions if humans hadn’t, over tens of thousands of years, developed the complex technologies needed to migrate from East Africa into new regions of the world. These technologies included warm clothing and shelter to protect from the cold, the domestication of plants and animals, stone tools to survive in new environments, and the ships needed to explore the Pacific Ocean!

Then, within each of the four world zones, new technologies were developed, new ideas circulated, and populations of humans became larger, making more complexity in each zone. Most complex of all, perhaps, because these four zones were relatively isolated from each other, their technologies and cultures were quite different from each other—so, each developed their own innovations independently.

Finally, these differences made it very interesting indeed when, around 1500 CE, humans began connecting the four world zones through a process that we call the Columbian Exchange. This exchange brought together four already-complex sets of crops, technologies, people, ideas, and cultures into one giant, global system.