Travel Reference
In-Depth Information
organized and augmented by Vincent Macauley of the University of Glasgow
and his colleagues. They found a remarkable pattern.
All the populations strung out along the route of the Great Migration
carry descendants of a mitochondrial chromosome, L3, that came from
Africa. And all the populations carry a mix of two descendant types of chro-
mosome, M and N. DNA base changes that accumulated in the M and N
chromosomes, however, are dif erent in the dif erent populations.
The dif erentiation into M and N took place about 65,000 years ago.
Within each of these sequence types there were further divergences, but these
additional divergences are unique to each population. Such a pattern could
only have happened if the original migrants had moved rapidly along the
migration route and the populations that they left behind remained isolated
from each other, free to diverge in dif erent directions. Once the colonies were
established, their mitochondrial chromosomes diverged independently of
each other, showing that the groups did not mix after the initial migration.
The data also showed that the Great Migration really did take place
along the southern rim of Asia, and did not branch of early to the north
as some paleontologists had proposed. The aboriginal peoples who fi rst
occupied regions that lie to the north of this route, in Taiwan and on the
eastern Asian mainland, carry samples of mitochondrial chromosomes that
began to diverge from each other more recently than at the time of the Great
Migration.
Of course, that 65,000-year date has a large error associated with it. The
authors suggest an error that could be as small as 3,000 or as great as 12,000
years. On the basis of this error, they estimate that the migrants could have
covered the entire 12,000-kilometer route of the Great Migration, from Africa
to Tasmania, at an average rate of between 1 and 4 kilometers per year.
At the slower rate, the migration would have taken 12,000 years, and at
the faster rate only 3,000. Obviously, whether the migrants moved quickly
or slowly, they did not travel at a constant rate. They must have leapfrogged
quickly along the more forbidding stretches of coast and dawdled in the
lusher regions. And even the shorter time span would have provided numer-
ous opportunities for tribal warfare. These wars and the great distances
involved split the migrants into factions.
