—By Geology: dating through study of rock formations and fossils found
with human remains. (Not very accurate)
—By Tree Rings: dating through study of annual rings which indicate
climate changes. (Accurate only in dry areas)
—By Carbon Fourteen: dating through checking amounts of radio-active
carbon in charcoal, shell and wood remains. (Accurate but difficult)
[Illustration: Cross section, east slope of Funeral Mound, Ocmulgee
National Monument. Arrangement of construction elements confused by
erosion and wash from top and side of successive mound stages.]
[Illustration: INDIANS COME TO THE NEW WORLD]
Most living American Indians share with the east Asians a group of
features which are considered to be distinctive of the great Mongoloid
division of mankind. These include: straight dark hair, dark eyes, light
yellow-brown to red-brown skin, sparse beard and body hair, prominent
cheekbones, moderately protruding jaws, rather subdued chin, and large
face. Since the question of race determination, however, is one of
extreme complexity, it should also be pointed out that while the
majority of modern Indians as well as prehistoric skeletal remains in
America share enough of these features in common to be regarded as
predominantly Mongoloid, they as well as the east Asians themselves,
possess other physical traits like stature and head form which vary
widely from group to group. Some of these other traits may be explained
by the influence of different environments acting over long periods of
time, but others point to an admixture of non-Mongoloid features in some
of the earliest migrants to these areas. It is just the meaning of this
mixture of apparently diverse elements which makes the problem of
ultimate origins so difficult; and we shall have to be content for now
with the general relationship which seems to have been established. If
the earliest wanderers to the Americas were primarily a blend of other
racial elements, their influence on the physical type of later American
Indians has been largely submerged by the Mongoloid features of the vast
majority of later arrivals.
Asia, too, is the closest great land mass to this continent, and from it
there are more practicable means of access than from any other area.
Even today the Bering Strait could be crossed by rafts, for islands at
the middle cut the open water journey into two 25-mile stretches.
Eskimos make the trip in their skin boats, or in winter by dog sled over
the frozen surface of the strait. In the past, the journey must have
been even simpler. During the several worldwide glaciations of the
Pleistocene Epoch, a geological period which began more than 600,000 and
ended about 10,000 years ago, great masses of ice spread across the
surface of the continents in the higher latitudes. Since the growth of
these ice sheets was nourished by falling snow, the seas, which supplied
the necessary moisture, were reduced in volume as the ice expanded. The
maximum drop in sea level has been calculated as between 200 and 400
feet, but the floor of Bering Strait is so shallow that a drop of as
little as 120 feet would have been sufficient to create a dry land
bridge between the continents. Further lowering must have increased the
area and elevation of this passage, but the main effect of this was
simply to extend the length of the interval during which the bridge
remained open. This may have continued well into the period of milder
climate after the time of maximum ice advance.
Another peculiar condition in this region at this time was the presence
of considerable areas untouched by glacial ice. These included the
foothills and coastal plain along Alaska’s northern coast as well as the
great central Yukon Valley. This surprising situation was probably due
to the small amount of moisture left in the winds which had passed over
the high and cold mountain chains bordering the southern coast and the
second great mass of the Brooks Range to the north. Furthermore, the
broad Mackenzie Valley, leading south along the eastern slopes of the
Rockies, was the area latest to be covered by glacial ice and first to
open up with the return of warmer conditions. It may even be that the
ice failed to cover this region during the last one or more of the minor
advances which together make up the latest, or Wisconsin, glacial
period.
Taken all together, therefore, the conditions described provided man
with a chilly but relatively dry and passable route from the Asiatic
mainland to Alaska and thence to the warmer interior sections of North
America. For a considerable period this route must have been flanked
with glacial ice lying only a few miles away on one side or both through
a total distance of some 2,000 miles. It is one of man’s distinctive
qualities, however, that he is able to adapt himself to extremes; and it
is probable that the game he lived on was itself acclimated to living
close to the edges of the ice sheets. We are less certain about the
conditions under which this journey was begun at its Asiatic end; but it
seems likely that there, too, ice would have formed in the high mountain
masses, but that the valleys and lowland would have remained open as
they did farther east.
We are confident in our knowledge of where man came from to the New
World and how he was able to make the trip. We are on less certain
ground, however, when we try to determine when he arrived. Estimates
have varied widely, changing with every increase in our knowledge. From
the first enthusiastic attempts to fit the Indian into the Old Stone Age
chronology which was just then unfolding for the Old World, the cold
reasoning of skeptical scientists brought down the maximum age of human
occupation of this hemisphere to something like 3,000 years. Beginning
in 1925, however, a series of finds has provided unquestionable evidence
that men using very distinctive weapons were living on this continent,
largely by hunting the mammoth and a great bison, both now extinct,
during the period when the ice was receding for the last time. The
typical channeled or fluted spear point of this people has even been
found lately along the northern Alaska coast. So, while we still cannot
say that this characteristic artifact was brought from Asia rather than
being developed here in America, it is at least an interesting
coincidence that man hunted large and now extinct game in Alaska in
areas where conditions were at times particularly well suited to his
immigration.
Other evidence shows that the users of this telltale point were not the
first to live in the region of the western plains; at least some of
their numbers had been preceded by men whose stone work was almost as
unusual and equally easy to identify. Recently developed methods of
dating by the use of radioactive carbon-14 show that the span of time
when the channeled point users, Folsom man, roamed the Plains included
one date of about 8000 B. C. For his predecessors, we feel justified in
pushing this date a good 2,000 or 3,000 years further back; and there
are even hints taken quite seriously by leading archeologists that man
was here many thousands of years before that. We know that the great
climatic swings marking the principal stages of the Pleistocene Epoch
were actually composed of repeated lesser pulsations. Like a mighty
pump, the changing climate worked upon all life within thousands of
miles of the shifting ice fronts, driving it southward with icy winds
and then sucking it back toward the north as cold and damp were replaced
by heat and drought. Man followed the game; and this, rather than any
planned migration, probably accounts for the wide spread of his earliest
remains.
American Indians, then, are most closely related to the present
inhabitants of eastern Asia, where they, too, had their origin. They
came to this country as its first human inhabitants some 12,000 to
15,000 years ago at the very least. They did not come all at once, or
even in one limited period of time, but probably in a fairly continuous
succession of small hunting bands following the game. Their earliest
migrations hither were doubtless the indirect result of great
fluctuations in climate which marked the coming and going of the ice
during the glacial age; and it was the peculiar conditions existing
about the present region of Bering Strait that encouraged them to
explore the now accessible region to the east. Once they had reached the
New World, their hunting travels probably carried them back and forth in
both directions so that a knowledge of the seemingly limitless territory
beyond became fairly general.
[Illustration: Broken Clovis point and sharp-cornered scrapers from
Ocmulgee excavations. Point length 3¹¹/₁₆ inches. Artist’s
reconstruction of point at left.]
The disappearance of the land bridge must have been very gradual by
human standards. Successive generations would have found the journey
increasingly difficult, but this would only have led to the adoption of
other measures such as waiting for winter ice or the use of rafts or
boats to cross the widening stretches of open water. Once arrived, they
began to spread out over the country, moving on as the game became
scarce to where it was more abundant, looking for new and unpeopled
areas whenever they began to catch sight too often of members of other
bands hunting the same territory. Not many years would be needed to
cover the vast expanse of the two continents. With movements of only 20
or 30 miles each year, it might have happened in as little as a dozen
generations; but we can say for sure that man had reached southern
Patagonia by about 6000 B. C., possibly far earlier. By then, we may
assume, the new homeland had been explored with some thoroughness; and
portions of it had already been inhabited for thousands of years. It was
by no means filled up; but many of its potentialities were known, and
American Indians were well started on their own peculiar course of
development.