[Paleopsych] ABC (au): A faster evolutionary clock?
checker at panix.com
Wed Dec 7 01:24:52 UTC 2005
A faster evolutionary clock?
[Analogy: when carbon 14 dating was first employed, it put Stonehenge later
than the Egyptian pyramids, though archeologists knew in their hearts that
this couldn't be true. When the Unchecked Premise, that cosmic rays
triggering off mutations comes in at a steady rate was Checker, new tables
were calibrated cross-dating from overlapping sets of tree rings. The result
was that Stonehenge turned out to be earlier than the pyramids after all.
[So maybe these out-of-Africa theories will get considerably revised and
theories of raciation before speciation into homo sapiens, like Carleton
Coon's, will get revisited. Stay tuned.]
Friday, 22 March 2002
A discovery by scientists studying ancient DNA from Antarctic penguins
may change our understanding of how fast the tree of life grew.
New Zealand scientist, Dr David M. Lambert, and colleagues report in
this week's Science on a new method of measuring the rate of DNA
They believe their method of using numerous samples of ancient DNA is
much more accurate than the current method of "calibrating" the
The team studied over 20 colonies of Adélie Penguins whose home is the
ice-free areas of Antarctica.
"This is the best source of ancient DNA found yet," said Dr Lambert,
of the Institute of Molecular BioSciences at Massey University in
By taking blood samples, Dr Lambert and colleagues were able to
analyse a particular segment of genetic material in the mitochondria
of the penguins and find two different groups whose DNA differed from
each other by 8%.
The team then set out to find when the two lineages diverged.
Conveniently, right beneath the very feet of the living penguins lay
the bones of their long gone ancestors - dating back to 7,000 years.
The researchers analysed equivalent DNA segments from carbon-dated
ancestral penguin bones of nearly 100 different ages ranging from 88
years to around 7,000 years old.
By plotting the degree of change in the DNA over time, they estimated
a rate of evolution equivalent to 96% per million years. This meant
the two groups of penguins diverged 60,000 years ago, in the middle of
the last ice age.
"This rate is 2 7 times faster than previous estimates for this
particular segment of mitochondrial DNA," said Dr Lambert. "According
to the standard rate of evolution, the penguins diverged 300,000 years
which is more than two ice ages ago."
The conventional method of calibrating the molecular clock involves
measuring the percentage difference between the DNA of two living
creatures and comparing it to DNA from a fossil counterpart of one
"This only gives you one data point a datum, not a distribution of
points," said Dr Lambert, "It is not statistically reliable whereas in
our method there is greater confidence in the numbers arrived at."
"We believe we've got a more accurate way of measuring the rate of
evolution," he said.
The findings may or may not have implications for other species.
"Maybe the Adélie penguins have evolved particularly fast," speculates
Dr Lambert. "We won't know until we apply the method to other
Dr Lambert and team now intend to test kiwis, Antarctic fish, the
Tuatara (a NZ reptile), and even humans.
Cape Adare in Antarctica is the largest colony of Adélie penguins
(Pic: J. Macdonald)
However, it won't necessarily be easy since the conditions required
for such an approach are quite particular.
The penguins in Antarctica were a perfect opportunity because they
provided a living population at the same location as dead ancestors,
the location was undisturbed by human influence, and the environment
was optimal for preserving DNA.
"Antarctica is not only cold, but it's drier than a desert," said Dr
Lambert. "It's not surprising it was the best source of ancient DNA."
"It'll be harder to do it for the other species but we've learnt a
lot, and we're going to give it our best shot," he said.
If the new faster rate of evolution proves correct for other organisms
this will change the our understanding of when different organisms
evolved, how fast the tree of life grew and even how different animals
responded to environmental change.
Anna Salleh - ABC Science Onlinee
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