The Great Migration - The Darwinian Tourist - page 240

As soon as the sand is covered and away from light, charges can gather
again and the clock begins to tick. When samples of sand from the excava-
tions are carefully gathered without exposing them to light, they will glow
when heated or irradiated with a pulse of light. The brighter they glow, the
longer the sand grains have been buried. Alternatively, the grains can be sub-
ject to a strong magnetic fi eld and then bombarded with microwaves that
cause the electrons to fl ip between charged states. This method also mea-
sures the strength of the accumulating charges in the sample. It has the pleas-
ing property that unlike the other methods it can be used over and over again
on the same material.
In a wide variety of sites around Australia and New Guinea, these tech-
niques and uranium isotope dating have revealed that humans fi rst arrived
at least 45,000 years ago, and perhaps as long as 60,000 years. 1 Some more
equivocal older sites have been found that may push human history in Austra-
lia and New Guinea back to even more than 60,000 years. But the confi rmed
current oldest data of 45,000 years has not yet been defi nitively breached.
Still, the time from 45,000 years ago to the present is a huge stretch of
history. Napoleon inspired his troops by haranguing them in the shadows
of the great monuments of Egyptian civilization, declaiming that forty cen-
turies looked down upon them. Four thousand years is a period of time
that encompasses most of Western civilization. But the Cockaded One was
boasting about less than 10% of the span of time that humans have inhabited
Australia.
What happened during all that time? The data are sketchy, but it appears
that the earliest migrants may have entered Australia by crossing a substan-
tial span of open sea from Timor and then spreading out over the rest of the
continent. Details are still unclear, but such an entry from the north is sup-
ported by the genetics of the present-day Aboriginal tribes. The most geneti-
cally variable tribes are found in the north of the continent, and variability is
reduced in the populations of the south and west. As we saw in the previous
chapter, such a pattern is typical of populations that spread by migration.
Figure 106 ( opposite ) A woman of the Tiwi Islands that lie in the Arafura Sea between Aus-
tralia and New Guinea. These people, isolated from the majority of the Aboriginal populations,
have developed their own culture and striking artistic tradition.