It may come as a surprise that the Kennewick Man is not the only, nor even the oldest human skeletal material we've recovered from the American continents. Indeed, there have been several, and somewhere in the range of seven to twelve of them dating between 8,000-11,000 years BP are adequately complete to allow full description. These include individuals from the Spirit Cave and Wizards Beach sites in Nevada; Hourglass Cave and Gordon's Creek in Colorado; the Buhl Burial from Idaho; and some others from Texas, California, and Minnesota, in addition to the Kennewick Man materials. All of them, in varying degrees, have traits that are not necessarily what we think of as "Native American;" some of these, like Kennewick, have been tentatively identified as "Caucasoid."
The Origins of Human Beings
To explain what a "Caucasoid" is, we'll have to go back in time a little--say 100,000 years or so. However, one of the reasons that physical anthropologists feel its so important to be able to study Kennewick man and his cohorts is that the theory is changing as I write this. Since the genetic investigations of the African "Eve" and a few other recent studies, understanding of the genesis of humankind and human "race" has undergone a substantial change, and is still, to be frank, in flux. What I'm about to lay out for you is the prevailing theory--but by no means the last or even the only current theory regarding human evolution.
Somewhere between 50,000 and 150,000 years ago, anatomically modern humans--Homo sapiens--appeared in Africa. Every single human being alive today is descended from this single population--and there is hardly any argument about that. At the time we are speaking, Homo sapiens wasn't the only species occupying the earth. Depending on which paleoanthropologist you speak to, there was at least one and perhaps several others (Homo neanderthalensis, Homo erectus, Homo rhodesiensis). There is some evidence, in a couple of places, that at least Neanderthals, modern humans and even Homo erectus shared our planet as recently as 40,000 years ago; Flores Cave may indicate H. Erectus as recently as 18,000 years BP. The tricky part is we don't really know the details of how these other species fit into our own evolutionary history. Did they impart some genetic material to us or not? That remains to be seen.
What we do know is that sometime after the appearance of modern Homo sapiens, some of us began to leave Africa and colonize the rest of the planet. As we spread out over the earth, little bands of us became geographically isolated, and began to adapt, as humans do, to their surroundings. Little isolated bands, together adapting to their geographic surroundings and in isolation from the rest of the population, began to develop regional patterns of physical appearance, and it is at this point that "races," that is, different characteristics began to be expressed. Changes in skin color, nose shape, limb length and overall body proportions occurred partly as a reaction to latitudinal differences in temperature, aridity, and amount of solar radiation. It is these characteristics that determine the "races" of our species; paleoanthropologists prefer to express it as "geographical variation," and that seems like a pretty good way to look at it. Generally, and I mean generally, the four major geographic variations are Mongoloid (generally considered northeastern Asia), Australoid (Australia and perhaps southeast Asia), Caucasoid (western Asia, Europe and northern Africa), and Negroid or African (sub-Saharan Africa). Bear in mind that these are broad patterns only and that both physical traits and genes vary more within these geographical groups than they do between them.
Thanks to Robert Franciscus, Shirley Schermer and Robin Lillie at the University of Iowa for assistance with this article.