Evolutionary answer to flatfish eye enigma

Chicago -- Fossils of two ancient flatfish prove the fish's asymmetrical, one-sided eye arrangement is a result of evolution, a study published Thursday said.

The highly specialized group of bottom-feeding fish -- which include sole, plaice, turbot, flounder and halibut -- originally had its eyes on both sides of its head, but one eye migrated over millions of years, 28-year-old University of Chicago doctoral student Matt Friedman said in an article published in the scientific journal Nature.

Until now, scientists have largely assumed the flatfish eye arrangement must have arisen suddenly because they could not see a benefit if it took millions of years, the Chicago Tribune reported.

Even Charles Darwin had trouble answering critics who used flatfish eyes as an argument against his evolutionary theory after he published it in 1859, the newspaper said.

But Friedman found several examples of different types of flatfish -- including a 50 million-year-old fossil recovered Verona,Italy -- that clearly showed one eye socket near the top of the skull, suggesting the eyes were "in transit" to the other side of the face, Friedman said.

In addition, a misclassified fossil that turned out to be an entirely new flatfish genus showed eyes clearly is in the transitional stage, he said.

Copyright 2008 by United Press International.