for National Geographic News
Using perfectly preserved, ancient DNA, scientists have demonstrated microevolution in a single species over a span of some 6,000 years.
The researchers examined well-preserved bones of Adélie penguins (Pygoscelis adeliae) found in Antarctica and compared them to the birds' living descendants.
The scientists discovered small changes in gene frequency, the relative percentage of an allele compared to nearby genes. Alleles are different forms of a gene (the code for blue or brown eyes, for example) that are inherited from each parent and that occupy a given space on a chromosome.
The evolutionary changes in the penguin genes have several possible causes. The most likely may be a recurring natural event in the birds' environmentthe mega-icebergs that intermittently alter the ways the penguins migrate and breed.
Biology professor David Lambert said that while many people might assume that natural selection propels evolution, "virtually all biologists define evolution as changes in gene frequencies over time."
Lambert, a researcher at the Institute of Molecular Biosciences at Massey University in Auckland, New Zealand, co-authored the new study. The findings were published yesterday in the Proceedings of the National Academy of Sciences Online Early Edition.
Until now, such gene frequency changes have only been measured over very short time scales. Some studies, for example, show contemporary changes in isolated populations of salmon or bird species.
But the preserved DNA of ancient Adélie penguins provided researchers with the opportunity for a much longer-term look at the process. The fossil bones contain the highest quality ancient DNA ever discovered, study authors say.
Adélie penguins breed in large colonies, ranging from 100 to 170,000 breeding pairs. The animals spend most of the winter on pack ice and invariably return to their birthplace to breed in ice-free coastal areas in summer.
Females usually produces two eggs, but almost a quarter of the chicks perish. This leaves large quantities of bones below the birds' nests that are preserved in distinct layers. Radiocarbon analysis can date the layers.
Put these circumstances together, and scientists are left with a bounty of DNA of known age andmost importantlyindividual ancestry.
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