Ancient Penguin, Bear DNA Reveal Pace of Evolution and Extinctions

By Bijal P. Trivedi
National Geographic Today
March 22, 2002

Ancient frozen bones excavated from Antarctica, northeast Siberia, the Yukon, and Alaska have yielded strikingly well preserved DNA that scientists are using to calculate how quickly life evolves and how it may have responded to climate change during the last ice age.

A recent report comparing DNA from ancient and modern penguins suggests that evolution may proceed much faster than previously calculated for penguins, and possibly other species. Another analysis of DNA from brown bears—some up to 60,000 year-old—revealed mysterious extinctions and sudden appearances of new populations.

Both reports are published in the March 22 issue of the journal Science.

Researchers led by David Lambert of Massey University in Palmerston North, New Zealand, collected DNA samples from 7,000-year-old nesting grounds of the Adélie penguin in Antarctica. Underneath the existing colonies lie layers of ancient frozen, fossilized penguin bones with DNA held suspended in time in the cold, dry conditions.

Comparing DNA from 96 penguin bones—some nearly 6,500 years old—with DNA from blood samples taken from 380 living Adélie penguins, Lambert and his colleagues calculated their evolution rate at between two and seven times faster than previous estimates.

"What is most surprising about Lambert's study," said evolutionary biologist Robert Wayne of the University of California–Los Angeles, "is that the evolutionary rate seems so high." Wayne cautioned that it is too early to say whether this rate applies to other species.

Bone Comparison

Lambert's team focused on DNA found in a special cell compartment called the mitochondria. Mitochondrial DNA is inherited directly from the mother without interacting with male DNA. "Mitochondrial DNA is particularly useful for constructing family trees and for studying the rate of evolution because mutations are easy to detect," said Lambert.

Lambert excavated bones from different depths, comparing DNA from each millennium with that in modern bones. This continuous DNA record enabled Lambert to directly measure the bird's evolution through time.

What distinguishes Lambert's study is that is "a completely new approach," said Wayne. Previous efforts to calculate the rate of evolution relied on either very few time points or rare fossil records. Some approaches have extrapolated evolutionary rates over millions of years based on genetic differences between just a couple of generations.

Using the faster rate of evolution, Lambert has suggested that two groups of Adélie penguins—the Antarctica lineage and the Ross Sea lineage—that differ genetically by about eight percent evolved these differences over only 60,000 years. Previous estimates suggested that this change would have taken at least 200,000 years.

Over the last 100 years, evolutionary biologists have tried to create a family tree showing the relationships between all living forms and to put a time scale on this tree, said Lambert. "Our study reveals that life may be evolving much faster than we anticipated," he said.

Lambert plans to use similar methodology to determine the evolutionary rate for the kiwi bird, a lizard called the tuatar, and a species of Antarctic fish.

Continued on Next Page >>




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