Charles Darwin is arguably the biggest name in biology.
He is credited with writing the first draft of the theory of evolution, which explains the origins of all species on earth.
He came up with this theory while watching finches on the Galapagos Islands. He noticed that all the finches were eerily similar but varied greatly in the size and shape of their beaks.
The beak of a finch is specialized for its specific diet. Some species of finch have delicate beaks for snagging insects, but others have gargantuan beaks built to crush even the most solid of seeds.
He proposed the finches diversified from a common ancestor as they grew specialized to different food sources.
This theory became a process evolutionary biologists now call adaptive radiation.
Since the time of Darwin, biologists have been grappling with the evolutionary process and the ways by which it proceeds.
In 1973, a pair of biologists from Princeton University, Peter and Rosemary Grant, decided the best place to study evolution is the place it all started: the Galapagos Islands.
Every year since then, the Grants have visited the Galapagos to observe evolution in action on Darwin’s finches.
In 2004 and 2005, a major drought struck the Galapagos, which gave the Grants a unique opportunity to see how populations of finches would respond to a severe lack of food.
They found the beaks of some species had changed after the drought in response to more severe competition.
The beaks of medium ground finches, which are normally large for cracking seeds, shrunk because another species of bird outcompeted them for the largest seeds.
The finches with larger-than-average beaks starved to death, leaving the smaller finches behind to feed on small seeds which didn’t interest the more competitive birds.
Until recently, biologists could only study how the physical appearance of the birds would change over time, but with modern sequencing technologies they now can look directly at the genes driving evolutionary change.
In order to look at how finch genes change in response to drought, the Grants and their collaborators sequenced the genomes of 120 individual birds covering all of Darwin’s species.
They were particularly interested in examining a gene known as HMGA2.
This gene is known to be involved in facial development in many animals and was recently shown to mediate beak shape and size in finches.
The researchers reasoned they should see change in the HMGA2 genes alongside changes in the bird’s beaks.
They identified variants of the genes associated with larger or smaller-than-average beaks, and in samples collected after the drought they found more birds with the small-beak version of the gene than the large-beak variant.
This result isn’t wholly surprising, but it is certainly cool because scientists can now look at the genes on which evolution acts.
While it doesn’t provide any earth-shattering answers, it does open the door to some new questions such as how these gene variants arise and contribute to splits between species.
Perhaps one day soon the Grants will find out and place more pieces in the evolutionary puzzle Darwin started almost two centuries ago.
jaykgold@indiana.edu
@jaykeche
