Curiosidades

["Xan M. Cainzos Prieto" <cainzos@...>]

Os mando esta curiosidad que encontre en Science Frontiers On Line:
http://www.knowledge.co.uk/frontiers
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WHEN HUMANS WERE AN ENDANGERED SPECIES

At one point during the last 400,000 years, the human population worldwide
was reduced to only about 10,000 breeding men
and women---the size of a very small town. What caused this population
"bottleneck"? Did a population crash engulf the
entire globe. If not, who was spared?

Such questions arise from a surprising observation: Human DNA is remarkably
uniform everywhere humans are found. This
hidden genetic uniformity is difficult to believe if one strolls through a
cosmopolitan city like New York or Paris. Nevertheless,
compared to the DNA of the great apes, whose mutation rates should be close
to ours, human genes on the average show
far fewer mutations. Human DNA from Tokyo and London is more alike than
that from two lowland gorillas occupying the
same forest in West Africa. Harvard anthropologist M. Ruvolo has commented:
"It is a mystery that none of us can explain."

The clear implication is that humans recently squeezed through a population
bottleneck, during which many accumulated
mutations were wiped out. In a sense, the human race began anew during the
last 400,000 years. Unfortunately, DNA
analysis cannot say where the very grim reaper came from.

(Gibbons, Ann; "The Mystery of Humanity's Missing Mutations," Science,
267:35, 1995.)

Comment. The hand that wiped the slate clean, or nearly so, might have been
a meteor impact, a pandemic, the Ice Ages, a
flood, volcanism, etc. Whatever it was, it seems to have largely spared
Africa. The chimps and gorillas there apparently did
not pass through the bottleneck. Even more interesting is the observation
that the DNA of Subsaharan Africans does shows
more variability and therefore seems older than that from humans elsewhere
on the planet. (See BMG9 in our catalog
volume: Biological Anomalies: Humans III.) Or perhaps Subsaharan DNA only
seems older because it was not forced
through that bottleneck. There are implications here for the African Eve
theory.

                         From Science Frontiers #100, JUL-AUG 1995. © 1997
William R. Corliss



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