Wednesday, May 11, 2016

Tale of Two Beaks: Darwin and the 21st Century

Fig.1. HMS Beagle in the Strait of Magellan (Credit: R.T. Pritchett, 1900

On 11 May 1820, the HMS Beagle was launched from the Woolwich Dockyard on the River Thames. Out of three voyages around the world to survey both land and sea, its second and easily most famous voyage cemented the ship’s role in history, thanks to the efforts of a young passenger named Charles Darwin. Now, nearly 200 years later, scientists have returned to the same birds that came to symbolize Darwin’s work in a study that captures evolution in action.

A Tale of Two Beaks

Researchers from Uppsala University in Sweden and Princeton University recently published an article in the journal Science that compared the genomes of Darwin’s finches to understand how a drought pushed evolution into overdrive. In 2004 and 2005, a drought on the Galápagos island of Daphne Major created competition for food between medium-sized ground finches (Geospiza fortis) with larger beaks and large ground finches (G. magnirostris) with similarly large beaks. More of the large finches survived, whereas only those ground finches with smaller beaks survived on smaller seeds. As expected, the medium ground finches after the drought tended to have smaller beaks than before.

The researchers identified the gene HMGA2 as the possible driver for the adaptation. When they analyzed the HMGA2 region in various finch species from before and after the drought, they found very clear differences between large- and small-beaked finches. Those medium ground finches that died out during the drought tended to have HMGA2 variants similar to large-beaked birds, whereas those that survived had HMGA2 variants similar to smaller-beaked birds.

These results might not be so surprising, except it is unusual for one gene to have such an effect on survival. Previous studies of possible genes affecting these finches’ beaks examined beak shape. This study, however, directly links beak size and the right species to surviving a drought. It seems like a very simple example of evolution on the molecular level, but it connects modern science to a theory developed in the 19th century that changed how we saw the world. 

Fig.2. Charles Darwin’s 1837 sketch of his first diagram
of an evolutionary tree 
(Credit: Charles Darwin

Evolution and the 21st Century 

In 1835, during Darwin’s stay on the Galápagos Islands, he failed to realize the significance of the numerous small birds with unique beaks. However, a meeting with ornithologist John Gould in 1837, just five months after his return to England, revealed that Darwin collected many new species specific to the islands. Even though he knew of only one type of finch on mainland South America, Gould identified at least 13 species of finches from the Galápagos, nearly 600 miles off the coast of Ecuador. 

There was no “eureka” moment that led Darwin to believe that species evolved rather than remain immutable through the millennia. His observations of both animals and plants encountered on the HMS Beagle, as well as later conversations with fellow scientists, planted the seed of an idea in his mind. For example, finches with large beaks ate seeds, whereas finches with slimmer beaks chased after insects. These specific traits allowed the birds to survive in their environment and not compete with each other for food. Individuals better adapted to their environments were more likely to survive and this survival influenced what traits offspring would have. This simple but powerful idea developed into the concept of natural selection, one of the basic mechanisms of evolution.

It would take another 22 years for Darwin to draw lessons from his travels and publish On the Origin of Species by Means of Natural Selection. Before Darwin's work was published, Alfred Russel Wallace contacted him about an independently conceived theory of evolution. This contact was the catalyst for Darwin to go public, and both men had their ideas presented at the Linnean Society of London in 1858. 

There are, of course, more figures and events in history that led to our understanding of evolution, beyond what can fit into one article. However, his work - grounded in the naturalist tradition to carefully observe and document the world around him - is still extraordinarily relevant today. The recent research with the HMGA2 gene is an elegant example of how theory from the 19th century is examined using modern molecular techniques. Studies to refine or redefine the theory of evolution are certainly expected in the future as technology advances, but it began with the launch of a small ship into uncertain waters 196 years ago. 

Bown, S. R. (2002). The Naturalists: Scientific Travelers in the Golden Age of Natural History. Canada: Ky Porter Books.

Lamichhaney, S., et al. (2016, April 22). A beak size locus in Darwin’s finches facilitated character displacement during a drought. Science, vol. 352 (6284): 470-474. Doi: 10.1126/science.aad8786

Sulloway, F. J. (2005, December). The Evolution of Charles Darwin. Smithsonian Magazine. Retrieved from

Thomson, K. S. (2009). The Young Charles Darwin. New Haven: Yale University Press. 

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