Galapagos Iguanas: Resolve a Challenge for Evolutionary Theory

In Spanish, the Galapagos Islands are called "Las Islas Encantatas" -- The Bewitched Islands -- maybe because of the strangeness of their plants and animals. Charles Darwin theorized that the unique species of the Galapagos Islands evolved from ordinary ancestors when variable offspring were able to exploit different opportunities on the islands and eventually separated into new species.

[Galapagos Iguana] To set the stage, Darwin's idea is explained to the students. Then students learn that the Galapagos have two kinds of iguanas: large land iguanas, and marine iguanas-- the only iguanas in the world that swim and dive.

So far, so good. But wait! According to molecular-biological dating, land and marine iguanas appear to have diverged from a common ancestor about 12 million years ago, but radioisotope dating of rocks gives an age of only 3 million years for the islands. How could the iguanas have split into distinct species to take advantage of opportunities on islands that did not exist when they split?

Students are invited to think of what kind of information they could use to help them resolve this problem. They can explore a collection of "articles," maps, and other data to support and test their idea. They will need to examine the assumptions of dating techniques, make analogies to distant islands, search the world for iguana fossils, and explore undersea terrain to gather relevant evidence. They will also learn why scientists don't simply discard established theories when confronted with a problem.

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(Galapagos Marine Iguana photo Courtesy Dr. Stephen Ervin.)

Last modified: Sun Oct 4 23:30:30 1998 -- Maintained by Dan Suthers, suthers@hawaii.edu