"The breakup of giant icebergs may have forced minor evolutionary changes in penguins over the past 6,000 years, a new study suggests. The Antarctic iceberg chunks, which break off the continent now and then, are thought to have blocked the swim paths of Adelie penguins returning home to their colonies. Some of the penguins were forced to become immigrants in other colonies, where they established new homes and interbred with the locals.
As a result, genetic changes that might otherwise have remained isolated became widespread among the different colonies. The result is what scientist call microevolution.
Microevolution involves small-scale genetic changes in a species over time. The classic example is a color change undergone by British pepper moths in response to changing levels of air pollution. The acquisition of antibiotic resistance by bacteria and the trend towards tusk-less elephants in Africa are also examples of microevolution at work.
Because it is so well documented, even people who don't believe that evolution can lead to the creation of new species accept that microevolution occurs.
Most microevolution studies involve change over very short time periods, on the order of decades or a few hundred years. The detection of microevolutionary changes over longer time periods has been difficult because it requires that ancient DNA deposits be found together with samples from modern populations of the same species.
Adelie penguins may be the ideal candidates for such research. The penguins often live, breed and die in the same colonies where they were born and where their ancestors before them lived. And the remains of ancestor birds are well preserved in distinct layers of the frigid terrain, making fossil dating relatively easy."
- From Ker Than, LiveScience.com
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