Current Data Concerning the Settlement of the Americas:
I often introduce my lectures on this topic by having my students read an article I lifted from the Internet from a site called "LiveScience" with the provocative title, "First Americans May Have Been European" (Carey 2006). It's such an excellent example of the manner in which journalists, and non-scientists generally, will latch on to a completely absurd hypothesis without a shred of evidence behind it and claim it throws doubt upon decades of careful empirical research.
In this article it is claimed that an "archaeologist" named Dennis Stanford, supposedly of the Smithsonian Institution, has argued that the original North American settlers could not possibly have come from Northeast Asia, which has been the accepted theory for decades. The only reason given is that the early North American Clovis tool complex does not look like tools from Siberia, but rather look more like the Solutrean tool tradition from Europe. From this single observation he then purportedly claims, against all evidence and reason, that the first settlers of the Americas must also have come from Europe.
After we all have a good chuckle concerning pseudo-science, and I refresh their memories concerning the nature of empirical evidence, I then proceed with my lecture.
In fact, there is little controversy in the archaeological literature over the question of where the first Americans came from. All the evidence points to northeastern Asia, as shall be discussed below. The only questions concern the matter surround the precise timing of the migration and the manner in which it was achieved.
It was long thought that the earliest settling of the Americas took place roughly 13,000-12,000 ya, but many now suggest that it could have taken place much earlier.
To begin with how people arrived here, however, one possibility is that people may have walked into North America from northeastern Asia. During glacial maxima, when sea levels dropped as much as 125 meters, a vast land area as much as 1500 kilometers across was exposed which linked Asia and North America. This "land bridge," called Beringia, is known to have been exposed intermittently between 75,000-35,000 ya (Hopkins 1982) and pretty much continuously between 35,000-11,000 ya (Yokohama et al. 2000), when the current interglacial began.
During these periods both people and animals could have migrated to North America on foot, and of course, that migration may not have been intentional. Hunters may have simply followed herds of animals as they moved about, eventually arriving in the Americas unknowingly.
Another consideration is that in historical times, long after the disappearance of the land bridge, the Bering Strait, which is only about 150 kilometers across in some areas, has frozen over in particularly cold winters. The same is likely to have happened periodically in the past, creating a more temporary ice bridge, which would have also allowed for easy movement between Asia and North America.
Given the fact that it is known that Australia was settled by a sea voyage of at least several 100 km by at least 40,000 ya (Birdsell 1977) , however, there is also no reason to exclude the possibility that North America was also settled by sea. Quite simply, there is no direct evidence to substantiate either the land bridge hypothesis, or the sea crossing hypothesis.
It does appear likely that the ancestors of contemporary Native Americans were populations of northeast Asians, however, and though the Siberian area has not been that well studied by archaeologists, it appears that the earliest evidence for human occupation of Siberia dates to between 30,000-20,000 ya (Feder & Park 2001). Thus, if we are correct that it was the ancient Siberians who migrated into North America, either over the land bridge, an ice bridge, or by boat, they would have had to settle Siberia itself first. The first settlement of the Americas, therefore, was likely no earlier than 30,000 ya, and very likely after 20,000 ya, since the earlier evidence in Siberia is rather scanty.
Despite Mr. Stanford's claims to the contrary, there is also some cultural evidence for Siberian populations being the first migrants to the Americas, since stone tools found in Siberia dating to roughly 18,000-14,000 ya resemble those of the Nenana Complex found in Alaskan sites around 12,000 ya (Powers & Hoffecker 1989). These include bifacially flaked spear points which are also similar to those found in other early American sites.
There may also have been more than one wave of migration into the New World. One site which may represent the habitation of some of the earliest migrants to the New World is the Bluefish Caves site, which is located near Beringia (Cinque-Mars 1978). This site has produced a wide variety of animal bones, some of which show evidence of butchering, as well as a variety of stone tools made from stone which was not available in the local area, suggesting that the stone or the tools were brought from somewhere else. Radiocarbon dates from the bones suggest an age of roughly 15,500-12,900 ya.
Unfortunately, there are few sites of this age in this area which can be used for comparison. As always it is possible that such sites may exist but have not yet been found. Alternately, the general absence of such sites may suggest that the long accepted route from Siberia through Beringia may not have been the route commonly used by settlers.
One problem with this theory is that during glacial maxima the route south into North America was often blocked by massive glaciers. Though we are uncertain of the timing, there does appear to have been periods when an ice-free corridor opened up between the two main ice sheets in North America, but this region may have been inhospitable to animals, and therefore of no interest to hunters.
There is, however, good evidence for human occupation south of the ice sheets prior to 11,000 ya. One such site is the Meadowcroft Rock Shelter near Pittsburgh, which is a small cave occupied over several thousand years. At the very base of the stratigraphic sequence over 400 tools were found, including a variety of blade tools and knives with retouched edges. These tools are associated with dates of between 12,800-12,000 ya, though the accuracy of these dates has been questioned due to the presence of natural coal in the area of the cave (Adovasio, Donahue & Stuckenrath 1990).
Other recent research has discovered sites which are potentially even older, including Topper Inn South Carolina, which may be as old as 20,000 ya and Cactus Hill in Virginia, which may date to 18,000 ya (Feder & Park 2001).
Yet another important early site is the Monte Verde site in Chile in South America. This site is situated in a deposit of wet peat, which led to a high degree of preservation of organic remains. Besides hundreds of stone tools, well preserved wooden lances and stakes that may have been used to hold down the bases of hide covered dwellings have also been found. Bones of a variety of animals have also been found, and even some preserved mastodon meat and skin. Though there is again controversy over the dates, radiocarbon dates place the age of this site at between 13,500-11,800 ya (Dillehay 1999).
This leads to the question of how migrants were able to reach the area so quickly if they were traveling by foot from Beringia. One theory is that rather than traveling overland, they may have used boats to travel along the coast. After all, we know that the Australians did so, and we also know that the Australian's first settled along the coasts.
The problem is that what was the North and South American coast at this time is now submerged, so that any evidence from that area is now difficult to recover. Underwater research has also been conducted, however, which suggests that the coastal environment would have been a more hospitable one than the interior at this time, and may have provided a viable route for the initial migration into the Americas (Feder & Park 2001).
In terms of human skeletal materials dating from this early period there is only a small sample of less than 30 individuals. Interestingly, these skeletons, such as the Keeniwick Man discovered in Washington State in 1996, resemble neither modern Native Americans nor modern Siberians, whose skeletal anatomy is similar. Instead, they more closely resemble the skeletons of the Ainu of Japan, southern Asians and Polynesians. This may simply result from the evolution of their skeletal anatomy over time, and the skeletons of ancient ancestors in many other parts of the world often do not match those of their modern, indigenous populations either (Feder & Park 2001).
In any case, based on /genetic/ similarities, northeast Asia is the most likely source for the people of America, and they may have arrived here either by land or by sea anytime after 30,000-20,000 ya based on the currently available evidence (Gibbons 1996).
References, additional readings:
J. M. Adovasio, J. Donahue & R. Stuckenrath (1990) "The Meadowcroft Rock shelter Radiocarbon Chronology-1975-1990, American Antiquity 55.
J. H. Birdsell (1977) "The Recalibration of a Paradigm for the First Peopling of Greater Australia," In: Sunda & Sahul: Prehistoric Studies in Southeast Asia, Melanesia & Australia, edited by Allen, Golson & Jones, Academic Press.
Bjorn Carey (2006) http://www.livescience.com/history/060219_first_americans.html February 19.
J. Cinque-Mars (1978) "Bluefish Cave I: A Late Pleistocene Eastern Beringian Cave Deposit in the Northern Yukon," Canadian Journal of Anthropology 3.
T. D. Dillehay (1999) "The Late Pleistocene Cultures of South America," Evolutionary Anthropology 7(6).
K. L. Feder & M. A. Park (2001) Human Antiquity: An Introduction to Physical Anthropology & Archeology, McGraw-Hill.
A. Gibbons (1996) "The Peopling of the Americas," Science 274.
D. Hopkins (1982) "Aspects of the Paleogeography of Beringia During the Late Pleistocene," In: The Paleoecology of Beringia, edited by D. M. Hopkins et al., Academic Press.
W. R. Powers & J. F. Hoffecker (1989) "Late Pleistocene Settlement in the Nenana Valley, central Alaska," American Antiquity 54.
Y. Yokohama et al. (2000) "Timing of the Last Glacial Maximum from Observed Sea-Level Minima," Nature, 406.