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Darwin's fishes: the threespine stickleback of the Pacific Northwest

Studies of a local fish are revealing fundamentals of evolution in action that Darwin could only dream of. Scientists have discovered the gene that gives these threespine sticklebacks different amounts of armor (stained red). In experiments, fish with the gene for light armor grew faster in fresh water, which may explain why and how sticklebacks lost armor after migrating from the ocean to lakes 10,000 years ago.