Scientists believe that many, if not all, of the first people in North America came from Asia.
About 12,500 years ago, they left what is now Siberia and walked over the Bering Land Bridge, now covered by water and called the Bering Strait, to Alaska.
The descendants of these first people may have eventually spread out into all parts of North and Central America, possibly reaching South America.
But some scientists are beginning to think that the Bering Land Bridge was not the only route to the Americas.
Remarkably, some people may have arrived by boat thousands of years before others walked across to Alaska.
They probably came at different times and from across both the Pacific and Atlantic Oceans to both North and South America.
One of every eight people in the world lives in North America.