Physical anthropologists are pretty much agreed on one thing--all of the earliest skeletal materials recovered from the Americas are different in appearance from any of the later Holocene occupants. Interestingly enough, they've known about that since the 1920s and perhaps earlier. A recent study of the available skeletal materials older than 8500 years ago included material from sites in Minnesota (Browns Valley, Pelican Rapids, Sauk Valley sites), Texas (Wilson-Leonard, Horn Shelter sites), Colorado (Gordon Creek), Arizona (Whitewater Draw). These sites included both specialist big game hunters and unspecialized hunter-gatherers. Despite their disparities in location and subsistence strategies, all of them were found to have similar physical characteristics--narrower and longer braincases and smaller and slightly narrower faces, compared to both North Asians and Native Americans. If you consider all the populations of the world, the Paleo-Indian group investigated have relatively broad faces; but northern Asians and American Indians have faces that are broader still. In fact, if you were to put characteristics of all the people of the world into one long continuum, at one end would be later Holocene north Asians and Native Americans, and at the other, southern Pacific and Europeans. Paleo-indians fall near the center of this continuum. Most interestingly, most of the early Holocene/late Pleistocene people (i.e. 8500 years and older) all over the Pacific Basin fall near the center of this continuum, and have the same general characteristics as the Paleo-indians of the Americas. These sites include the Upper Cave at Zhoukoudien, several Jomon sites in Japan, and the Minatogawa site on Okinawa Island.
Mitochondrial DNA and American Colonization
A second clue to determining who the earliest colonists of the new world were is found in recent genetic studies. Geneticists have identified four founding lineages among the American Indians of both North and South America, expressed in mitochondrial DNA. Previous studies were said to have resulted in the identification of three separate "waves of migration," based primarily on language studies--Amerind, NaDene, and Eskimo/Aleut. The four founding lineages are each found in each of the three groups; in other words, all three "groups" are close genetically--they're not separated groups. Let me restate that: There is increasing evidence that all Native American groups are closely related, and that the "three migrations" identified by the linguists are not supported at the genetic level.
Founding the Americas
What geneticists are beginning to believe is that the founder population of all of the Native Americans, and indeed most of the peoples of the Pacific Basin, are descendants of a group of individuals who lived in Mongolia some 20,000-30,000 years ago, individuals who looked very much like the Paleoindians of the New World. And that the characteristics that we recognize as "Native American" or "Asian" developed after the migration into the American continent and away from the Mongolian basin.
One mind-boggling possibility is, you see, that most of the geographic variations that we see in one another, those characteristics that we use to discriminate one "race" from another, developed around the time we developed agriculture; no earlier than 10,000 years ago anywhere on the planet.
What does Pre-Clovis Mean?
When Kennewick Man was discovered, archaeologists really didn't know what Pre-Clovis might have looked like. Research since that time have discovered many surprising traces of the earliest human colonizers of the Americas: they were not big game hunters, but rather economically broad-based fisher-hunter-gatherers.
See the Pre-Clovis glossary entry for more details. Kennewick Man Table of Contents | Part 4: How Were the Americas Populated? | Part 5: What does "PreClovis" Mean? | Part 6: How NAGPRA Affects Kennewick Man