Description:After Charles Darwin first visited the island archipelago of Galapagos in 1839, it took him another twenty years to decipher the scene he'd witnessed, the most perfectly preserved biodiversity on the planet. His theory of evolution - published 150 years ago - pulled back the curtain on a debate that had been simmering for years, and still percolates. Today Darwin would be surprised by the tourist mecca Galapagos has become; 200,000 visitors a year, 40,000 permanent residents. (25:35)