Tag Archives: Darwin

Darwin’s Finches

The Galapagos Islands constitute a small group of about a half a dozen islands 600 miles off the coast of South Ameria. The total land area is a scant three thousand square miles, slightly larger than the state of Delaware. The islands are quite arid, averaging only two inches of rainfall a year. They are essentially the cones of volcanoes which arose from the sea a few million years ago.

The archipelago is most famous as a world heritage site and most of the islands are a national park. As a province of Ecuador, the islands are managed mainly and very carefully for preservation and tourism.

One of the first and certainly most notable “tourists” was Charles Darwin. In 1831, Darwin, as a 22-year-old naturalist and recent college graduate signed on to the HMS Beagle for a five-year sail around the world. The Beagle surveyed much of the coast of South America, including the Galapagos. Darwin’s time was spent observing and collecting specimens of the local flora and fauna.

As a geologically young island group, the flora and fauna found their way by air and sea. Sea birds flew, sea lions swam, and a few reptiles and small mammals “rafted” to the islands. When Darwin arrived he noted that there were very few passerines, what we call perching birds or songbirds. Of the passerines, the majority were finches – finches not seen anywhere else in the world. There are now seventeen species of finches recorded on the Galapagos.

Darwin’s observation of the finches was the seminal study that lead to the organizing tenet of biology – descent with modification. Only a single species of finch exists on the west coast of South America, the likely origin of the Galapagos finches. Darwin’s conjecture was that a single species of finch arrived accidentally on the island group.

With local no predators and few competitors, the finches thrived. Through adaptive radiation, they filled many different niches based on the size and shape of their beaks. Birds with big, strong beaks could crack larger seeds, smaller-beaked birds ate smaller seeds. Birds with narrow, pointy bills fed on insects. There is even a species of finch appropriately called the vampire finch that has adapted to pecking the tails of sea birds to drink their blood!

In his first book, “The Voyage of the Beagle,“ he noted “It is very remarkable that a nearly perfect gradation of structure in this one group can be traced in the form of the beak, from one exceeding in dimensions that of the largest gros-beak, to another differing but little from that of a warbler.”

The speciation of these finches is a microcosm of evolution on our planet. Life began over three billion years ago, and for about two billion of those years existed as single-celled organisms much like today’s bacteria. Over time more complex organisms evolved to form the major groups of plants and animals. These discoveries are the essence of science – small careful observations can lead to profound conclusions.
Dr. Bob Allen, Ph.D., is Emeritus Professor of Chemistry at Arkansas Tech University.