What's the big deal about Darwin's finches?

Like Newton’s apple and Archimedes’ bathtub, Charles Darwin’s finches rank among history’s most famous emblems of scientific discovery.

But do the birds really deserve their lofty status as mascots for evolution? Darwin definitely saw and collected a number of finches during his voyage through the Galapagos Islands in 1835, and the varied shapes of their beaks certainly caught his eye.

"Seeing this gradation and diversity of structure in one small, intimately related group of birds," he wrote in his book, The Voyage of the Beagle (see the image from the book at right). "One might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends."

At the time scientists thought species were fixed, that they didn't change over time – hence Darwin’s use of the word ‘fancy’. Little did he know that his whimsical observation was about to launch a revolution.

But tying Darwin’s name to the finches oversimplifies things – it was ornithologist John Gould who in 1837 first identified the birds as belonging to 12 different species (there are fourteen species of finches) did the first in-depth study of the birds.

Gould’s work did indeed inspire Darwin; he features the birds in his 1859 masterpiece On the Origin of Species.

And the finches – much like Darwin’s theory of natural selection – continue to inspire scientists to this day. Peter and Rosemary Grant, biologists at Princeton University, have made studying the birds their lives’ work, and have unlocked a series of evolutionary mysteries in the process.

In a recent paper published in the journal Molecular Biology and Evolution, the husband wife team led a group of researchers in a study that traced the origin of Darwin's finches. In a DNA analysis of the14 finch species now living in the Galapagos Islands, plus one living on Cocos Island, they found that all descend from a common relative, a grassquit finch called Tiaris obscura.

Tiaris obscura migrated to the Galapagos Islands about 2.3 million years ago, where they found lots different sources of food. Their beaks quickly started to diversify, changing shape to take advantage of their preferred diet in a process known as adaptive radiation. 

An article published in New Scientist in 2006 discusses the Grants’ astonishing finding that the birds’ beaks could change in just a few years. When a drought in 2003 and 2004 changed the available food sources for some of the finches, they adapted. Smaller-beaks specimens of the species Geospiza fortis were more likely to survive because they could eat smaller seeds. By 2005, the beaks of Geospiza fortis were 5 percent smaller on average.

Such rapid evolution appears to be more common in animals than we ever thought possible. The finding is changing the way biologists study the animal kingdom, much like Darwin’s theory of natural selection did, almost two hundred years earlier.

Learn more about evolution at HowStuffWorks.com:

• How Evolution Works 
• How Natural Selection Works 
• How can two seemingly unrelated species that live in isolation from each other evolve into identical forms?