Dr. Jon Driver
Department of Archaeology, Simon Fraser University
You might ask why it is that we don't find evidence for people living in the Americas much earlier than the current dates would suggest. One of the reasons is that people evolved in Africa and they began to spread out of Africa perhaps 100,000 years ago. As they spread out of the warm tropical countries, they had to learn how to live in the cooler climates. They had to develop techniques for hunting animals in those environments, they had to be able to make shelters, they had to find ways to make warm clothing, and they had to be very good at making fires so that they could stay warm in the cold winters. If you think about the problems of living in an arctic environment, living in a very cold environment where the sun doesn't shine for part of the year, and where you absolutely have to rely on hunting and staying warm in order to exist, then you can imagine it would take many thousands of years for people to develop all the techniques necessary to get into the arctic environments.
Now the problem in terms of the Americas is that, in order to travel to the Americas, you've only got two options: first you take the land bridge, the land route that goes out of Asia, across what is now the Bering Strait and into what is now Alaska. In order to do that, you've got to travel through very cold arctic conditions. So we don't think people were able to do this until they had adapted all the right tools, all the right technologies, and had acquired a level of knowledge to enable them to survive in the arctic.
The other possible ways to get to North America or South America are by boat. So, for example, people could have sailed a boat from Africa to South America, or they could have sailed a boat from Europe to North America. This is a plausible hypothesis, it's something that we ought to explore, but we have absolutely no evidence that the earliest people who made it to the Americas came by boat. First of all, we don't have any evidence in Europe or Africa that these people were capable at this time of undertaking long sea voyages. Secondly, we have no artifacts, anywhere in North America or South America, that are similar enough to artifacts in Europe or Africa to suggest that the first people to colonize the Americas crossed either the north or the south Atlantic.
Going to the other side of the continent, it is very, very unlikely that people came across the Pacific because all of the archeological work that has been done on the islands of the Pacific, for example in the islands of Polynesia, suggests that people only got to those areas about 3,000 years ago, and that is much too late to account for the peopling of the Americas.
So, right now, there are really two plausible hypotheses for how people entered the Americas: they either came by boat, and we don't have any evidence for that, or they crossed the Bering land bridge, moved into Alaska, and then moved further south. In terms of moving further south, assuming that they came during the ice ages, then there were really only two routes they could have taken. For many years, archeologists have hypothesized that people came from the interior of Alaska; they came down the Rocky Mountains where there was a corridor between the glaciers in the mountains and the glaciers that were out on the Canadian plains and the Canadian Shield. The other hypothesis, and one that has been proposed more recently, is that, rather than coming down what archaeologists have called the ice-free corridor, the earliest people migrated down the coastline, so down the Alaska coast and then down the British Columbia coast, until they got south of the ice sheets. At that point, they were able to move inland and colonize what is now most of North America and then all of South America.
The argument that people moved down the coast, perhaps with the help of boats, has been growing in strength over the last few years, while the hypothesis that they came down the ice free corridor in the interior of the continent has been losing ground. There is less evidence to support that than there used to be.