Newly evolved finch appears on the Galapagos Islands

Evolution caught in the act? An isolated population of finches have odd-shaped beaks, sing differently, and don't breed with others.

By Bryan NelsonMon, Nov 16 2009 at 9:40 PM EST

NEW SPECIES: Scientists studying Darwin's finches in the Galapagos are witnessing evolution in action. (Photo: Grant, P./PNAS)

Just a few years ago, the husband and wife team of Peter and B. Rosemary Grant made the breakthrough discovery that the beak sizes of some of the finches on the Galapagos Islands had already changed since Darwin's visit in 1835. Now they believe they may have witnessed the evolution of a brand new species.

Even more remarkable, the scientists have tracked the evolution of the new lineage back to a single bird. As Nature reports, it began in 1981 when the Grants spotted an unusually heavy, medium ground finch (Geospiza fortis) on the Galapagos Island of Daphne Major. At 29.7 grams, the male was markedly heavier than any of the other finches they had found there. Genetic analysis revealed that the odd bird likely came from the neighboring island of Santa Cruz, where the species is larger.

The Grants marked the bird with the number 5110, and proceeded to follow it over the course of seven generations. Because 5110's descendants had different origins than other, smaller Geospiza fortis found on Daphne Major, they also had unusually shaped beaks and grew up learning to sing different songs. Since finches use their beaks and their songs to identify suitable mates, the population began to isolate itself from others.

Then in the fourth generation, tragedy struck 5110's family. A severe drought parched the entire island, leaving only two living descendants — a brother and a sister. From that time forward, the outcasts became permanently isolated, refusing to breed with any other G. fortis on the island.

While the Grants aren't quite ready to call the isolated lineage a new species yet, they acknowledge that if the birds continue to remain isolated, speciation will be inevitable. "There is no non-arbitrary answer to the question of how many generations should elapse before we declare the reproductively isolated lineage to be a new species," they said. "[But] for the present it is functioning as a [separate] species."

And it's unlikely that the population would breed with any birds from their original home in Santa Cruz either. Although these finches learned their songs from their father, and thus derived it from 5110's original home in Santa Cruz, they have already developed a thick accent. It's likely that over time, the song mishmashed from its original version while the birds attempted to copy the music of Daphne Major's other finches.

"No study of this sort has been done before, and it shows one way in which speciation can get started," said the Grants from Japan, where they are set to receive the Kyoto Prize for basic science for their life work.

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