Africa Speaks Reasoning Forum

The following points are made by Tom D. Dillehay (Nature 2003
425:23):

1) Questions of which human populations first arrived in the
Americas, and when, where and how this happened, have been
debated by researchers for decades(1). It has long been presumed
that the first people entering the New World were the direct
ancestors of present-day Native Americans and that they arrived
in America from northeast Asia about 12,000 years ago(2). But
this theory has been challenged by new archaeological discoveries
and by findings of early human remains bearing anatomical
similarities to the people of south Asia and the southern Pacific
Rim(3,4). González-José et al.(5) have add more fuel to this
heated debate. They present a comparative study of early historic
human skulls from Baja California, Mexico, and their findings
lend weight to the view that not all early American populations
were directly related to present-day Native Americans.

2) Human skeletal remains have long been used by
palaeoanthropologists to model early human migration. The
conventional view is that different skeletal populations with
similar craniofacial features (skull form) shared a common
ancestry and were genetically related, whereas different features
reflect different ancestry. Migration histories and evolutionary
forces explain the similarities or differences.

3) Piecing together the ancestry of the Americas has been
difficult, as early human remains dating from about 10,000 years
ago (the end of the last ice age) are fragmentary and scarce.
Scientists have typically reconstructed the missing pieces of the
most ancient skulls by extrapolating backwards from later, more
complete skeletons. Ancient American skulls reconstructed in this
way were anatomically indistinguishable from early northeast
Asians and also from present-day Native Americans(2). So a theory
arose, supported by dental and other archaeological data, that
the first humans entering the Americas were northeast Asians who
arrived in three successive migrations beginning around 12,000
years ago. These founding colonizers were thought to be big-game
hunters, equipped with so-called "Clovis spears", who rapidly
populated the Western Hemisphere and gave rise to present-day
Native Americans.

4) But more recent archaeological discoveries suggest that there
were several different founding populations, arriving from
different places, each with different lifestyles and
technologies. Some populations not only hunted big game but also
exploited a wide range of plant and animal life. To complicate
matters further, it is no longer certain that the first
colonizers arrived about 12,000 years ago -- some archaeological
sites in South America date from 12,500 years ago, which suggests
that the first humans arrived at least 15,000 years ago.

References (abridged):

1. Dixon, E. J. Quat. Sci. Rev. 20, 277-299 (2001)

2. Dalton, R. Nature 422, 10-12 (2002)

3. Neves, W. A. & Pucciarelli, H. M. J. Hum. Evol. 21, 261-273
(1991)

4. Dillehay, T. D. The Settlement of the Americas: A New
Prehistory (Basic Books, New York, 2001)

5. González-José, R. et al. Nature 425, 62-65 (2003)

Nature http://www.nature.com/nature