When Charles Darwin collected finches from the Galapagos Islands, he hadn’t yet hit upon his theory of evolution. It was only later, after his samples had been examined by his friend, the ornithologist John Gould, and confirmed as different species that the idea began to take shape.

In the end, however, the unique beak shapes of the Galapagos finches played a key role in demonstrating the idea of evolution by natural selection.

Darwin’s finches have become a classical example of what is known as “adaptive radiation”. Since the common ancestor of the Gallops finches arrived there more than 200 million years ago, the finches have divided into 15 known species. The animals vary by beak shape, body size, feeding behavior and song, each adapted to the particular island on which it lives.

Now, just a day before the 206th anniversary of Darwin’s birth a team of researchers from Uppsala University and Princeton University has done what Darwin couldn’t, examined the birds by sequencing their genomes.

“We have now sequenced 120 birds including all known species of Darwin’s finches, as well as two closely related species in order to study their evolutionary history”, explains Sangeet Lamichhaney in a statement.

Laminchhaney is a PhD student and shared first author of a paper published in the journal Nature.

For the study, each species was examined and members of a single species from up to six islands were sampled to look for further adaptations.

One important finding of the team was that gene flow between species has played a prominent role through the history of the finches.

The University of Berkeley’s Understanding Evolution website describes gene flow as “…any movement of genes from one population to another. Gene flow includes lots of different kinds of events, such as pollen being blown to a new destination or people moving to new cities or countries. If genes are carried to a population where those genes previously did not exist, gene flow can be a very important source of genetic variation.”

This indicates that the various species on individual islands haven’t remained completely isolated from one another but have interbred, sharing genetic information and adaptations between groups.

The researchers were able to specifically trace hybridization between a warbler finch and a common ancestor of tree and ground finches which occurred about a million years ago.

“During our field work on the Galapagos we have observed many examples of hybridization between species of Darwin’s finches but the long-term evolutionary effects of these hybridizations have been unknown”, say Peter and Rosemary Grant, Princeton University, who know are considered the world’s leading experts on Darwin’s finches after 40 years of studying them.

“Now we can safely conclude that interspecies hybridization has played a critical role in the evolution of the finches, and has contributed to maintaining their genetic diversity”, added Peter Grant.

The most striking diversity found by the researchers was the the same as that most notable to Darwin and Gould, the size and shape of the beaks. This diversity, along with comparisons to beak diversity among European birds, was discussed by Darwin in “The Voyage of The Beagle”.

The different beak sizes and shapes have allowed the birds to exploit a variety of food sources including seeds, nectar, insects and iguana blood.

The team investigated the beak variation by comparing two species with blunt beaks with two species with pointed beaks. In total, 15 variations in the genome stood out including six specifically associated with beak development.

“This is an interesting example where mild mutations in a gene that is critical for normal development leads to phenotypic evolution”, comments Leif Andersson, Uppsala University, Swedish University of Agricultural Sciences and Texas A&M University, who led the study.

A complete archive of Charles Darwin’s papers and published works is available at darwin-online.org.uk.