A blue whale, the largest animal on the planet, engulfs krill off the coast of California. Silverback Films/BBC/Proceedings of the Royal Society B hide caption

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Silverback Films/BBC/Proceedings of the Royal Society B

The Two-Way

How The Biggest Animal On Earth Got So Big

Whales might be the largest animals on the planet, but they haven't always been so huge. Researchers say the ocean giants only became enormous fairly recently, and over a short period of time.

Soccer midfielder Julie Foudy (right) cheers her teammate, Tiffany Roberts, during the WUSA All-Star Game on June 19, 2003 in Cary, N.C. Al Bello/Getty Images hide caption

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Al Bello/Getty Images

A Message To Inspire Women To Lead: Own Your Awesome

Audio will be available later today.

A blue whale, the largest animal on the planet, engulfs krill off the coast of California. Silverback Films/BBC/Proceedings of the Royal Society B hide caption

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Silverback Films/BBC/Proceedings of the Royal Society B

How The Biggest Animal On Earth Got So Big

Audio will be available later today.