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DNA extracted from
teeth in a human mandible, recovered from an island cave off southern Alaska,
may provide clues to the route taken by the earliest migrants to the Americas.
Representing the earliest human DNA ever isolated in the Americas, the sample,
according to molecular anthropologist Brian Kemp, includes fragments of both
mitochondrial DNA (mtDNA) and Y chromosome DNA. The teeth came from the mandible
of an adult male discovered with associated pelvis bones in 1996 in On Your
Knees Cave on Prince of Wales Island (fig.1). This ancient stratigraphic
level also contained obsidian microblades, other stone bifaces, and a bone
tool dated by AMS (accelerator mass spectrometry) to 10,300 +/- 50 BP
(AR 3,2). This is currently the oldest artifact from the Northwest
Coast whose date is widely accepted.
According to E.
James Dixon, principal investigator of archaeology at the cave site (officially
known as 49-PET-408), humans were exploiting the maritime restwater
fish, sea mammals, and shellfish (Dixon 2002; AR 3,2). Given
the ources of the
Northwest Coast by at least 9,500 BP (or 10,150 cal BP). Isotopic analysis
of these human remains showed he typically ate maritime food, including salcave's location 1 km from the coast, combined with the presence of non-local obsidian and a maritime diet, Dixon concluded that the ancient  inhabitants
were coastal navigators with established trade networks. Additional evidence
for early maritime adaptations and the use of boats or rafts also occurs
at other coastal sites from Santa Rosa Island off California to Ecuador and
Peru. Dixon and other researchers have suggested that the first human entryway
into the Americas may have occurred along the west coast through the use
of watercraft.
Fig.1: Location of 49-PET-408 on Prince
of Wales Island and obsidian sources on Sumez island and Mt. Edziza (after
Eric Parrish).
DNA recovered from
the 49-PET-408 individual appears to support this coastal migration theory.
The DNA was compared with mitochondrial DNA from more than 3,000 Native American
sequences taken from public databases. Matches were obtained from samples
of modern and ancient individuals, with the coastal Cayapa of Ecuador accounting
for more than 50% of the matches. Others included the Chumash (California),
the Klunk Mound people (Illinois), the Tarahumara (Chihuahua, Mexico), and
the Mapuche and Yaghan tribes (Chile) - thereby tracing a possible migration
route.
Current molecular
genetic studies of human mtDNA suggests that five founding lineages were
responsible for the colonization of the Americas over 10,000 years ago (Schurr
2002). The four principal lineages (also known as haplogroups), designated
A-D, account for over 95% of all mtDNAs of modern New World indigenous
populations, as well as the majority of mtDNAs of ancient Amerindian populations.
The man from On Your Knees Cave belonged to lineage D, found in significant
frequencies among Patagonian Amerindians (over 50%); Andean Amerindians (~33%);
Amazonian Amerindians (~33%); N. American Amerindians (10%); US SW Amerindians
(5%); Aleut (75%); and Eskimos (~23%) (Schurr 2002: fig.5). A fifth lineage,
designated X, is present among a very restricted number of populations.
Comparative studies
of these genetic lineages are leading to a better understanding of the ancestry
of Native Americans and the timing of the first colonization of the New World.
Haplogroup A-D mtDNAs occur together in Asian populations from the Altai
Mountain region to Japan and Korea. Significant frequencies of Haplogroup
C and D mtDNAs, moreover, are found in all eastern Siberian populations,
and are also present in many East Asian populations (Schurr 2002). The timetable
for the arrival of these lineages in the New World has been the subject of
considerable research, with current estimates of arrival based on molecular
studies ranging from an "early" entry of 35,000-20,000 cal BP to a "late"
entry of 14,000-12,000 cal BP) (Schurr 2002).
Recent studies of
Y-chromosome variations (transmitted only from father to son) have been tracking
male migrations in time and space. With Y-chromosome DNA successfully extracted
from the On Your Knees man, comparisons with the rapidly expanding genetic
database should provide additional insights to his molecular makeup and
affinities.
As a footnote to
the investigations at On Your Knees Cave, archaeologists and the local Tlingit
and Haida tribes, in contrast to the conflict surrounding Kennewick Man,
have cooperated in the ongoing quest to learn more about the earliest traces
of humans in the Americas.
References:
Dalton, R. "Caveman DNA hints at map of migration."
Nature 436:162; Dixon, E.J. 2002. "How and When did People First Come to
America?" Athena Review 3,2:23-27; Schurr, T.G. 2002. "A Molecular Perspective
on the Peopling of the Americas." Athena Review 3,2:62-75;
http://www.usd.edu/esci/alaska/ oykc.html
This article appears on pages 8-9 in Vol.4 No.2 of Athena
Review.
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