Homo Erectus was found to live in China as far back as 750,000 years, so they would have had probably as many as 8 chances to get to the Americas. That we haven't found any fossils means either they never went over, or that we simply haven't found any evidence yet. Given the numbers of species that did cross over, I'd wonder why they didn't.
Except Beringia (The land bridge between Siberia and Alaska) was never glaciated.
The term Beringia was first coined by the Swedish botanist Eric Hultén in 1937. During the ice ages, Beringia, like most of Siberia and all of Manchuria, was not glaciated because snowfall was very light. It was a grassland steppe, including the land bridge, that stretched for several hundred miles into the continents on either side. It is believed that a small human population of at most a few thousand survived the Last Glacial Maximum in Beringia, isolated from its ancestor populations in Asia for at least 5,000 years, before expanding to populate the Americas sometime after 16,500 years ago, during the Late Glacial Maximum as the American glaciers blocking the way southward melted
It requires sufficient glaciation in the rest of the world to drop sea levels enough to expose the seabed. I can't find the information that says exactly when Beringia appeared and when it didn't. Still looking.
*Never mind, I misread your post.
Edited by Slave2Fate, 14 June 2014 - 05:11 AM.