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found along with the skulls. But White and his colleagues pointed out that
these skulls were distinctly dif erent from those of present-day humans—
their brain cases were unusually large, and the skulls had slightly projecting
brow ridges. They gave these fossils a new subspecies name,
idàltu
, which
means “elder” in the local Afar language.
It is not surprising that
Homo sapiens idàltu
dif ered from us. A hundred
and sixty thousand years is almost 10,000 human generations, plenty of
time for genetic changes to accumulate. But let me again emphasize that
even those ancient people are part of a continuum. Much older fossils of
peoples who still show signifi cant resemblances to modern humans have
been found, especially in southern Africa.
Suppose we were to climb aboard a time machine and go back to the
period of our mitochondrial Eve, roughly the time of
H. sapiens idàltu
, and
suppose further that we could actually track the Eve down. She might have
been a member of that Ethiopian tribe, but she was much more likely to have
lived somewhere else in eastern or southern Africa.
If we could obtain mitochondrial DNA samples from her and from her
contemporaries around the African continent, we would fi nd that they dif-
fered among themselves because of accumulating mutations that had taken
place in their past. The mitochondrial Eve's chromosome would simply be
one of these sequences. Its only distinguishing characteristic was that it was
the one that would survive and give rise to all of today's descendent mito-
chondrial chromosomes.
If we then traced this collection of lineages back in time, we would be
able to infer the existence of an earlier mitochondrial Eve. Probably that Eve
would have belonged to one of those earlier South African peoples that had
some modern characteristics.
In short, there would have been nothing unusual about the woman who
happened to carry the mitochondrial Eve chromosome. It is even unlikely
that she lived at a particularly dramatic time in our evolutionary history. She
was a tiny part of the great and continuing pageant of our evolution. The fact
that she carried the mitochondrial chromosome that has been passed down
to all of us is a statistical accident.
