Ecuador

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Galápagos Islands, Ecuador

0° 40′ 0″ S, 90° 33′ 0″ W

The Second Voyage of the Beagle

The Galápagos Islands are an archipelago of volcanic islands about 1,000 kilometers off the coast of Ecuador in the Pacific Ocean. They were visited in 1835 by the British survey ship HMS Beagle, which sailed from 1831 to 1836 around South America and on to Australia before returning to Britain, gathering information along the way about safe landing places and navigable rivers. The most famous passenger aboard was the 22-year-old Charles Darwin.

Darwin spent most of the voyage ashore, surveying the geology of the land and collecting specimens of local fauna, flora, and fossils. As the voyage progressed, he kept a journal, and copies of the journal and his specimens were sent back to Britain. By the time Darwin returned home, he was a minor scientific celebrity.

Unbeknownst to his shipmates, the ideas that would become his famous theory were forming in Darwin’s mind during the voyage. A year after his return, Darwin sketched his “tree of life” diagram in a notebook, and went on to work out the theory of natural selection.

On the voyage, Darwin spent over a month surveying the Galápagos Islands. Because the islands were far from the nearest land, and because there were so many of them, they made an ideal location for observing different varieties of the same species. Darwin noted that tortoises, mockingbirds, and finches were present on different islands, but differed from island to island.

The finches were a key clue to the theory of natural selection, although Darwin thought that the birds he had collected on different islands were unrelated. It was only upon his return to London that it became clear that these were 12 species of finch dissimilar from any other finches in the world. He reasoned that the finches had evolved specific beak sizes and shapes because of different sources of food on the various islands, writing:

Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.

Today, almost all of the Galápagos Islands are a national park, and the surrounding sea is a marine sanctuary.

By far the best way to see the islands is to book a boat tour that hops from island to island (especially important to get a feel for the different habitats that helped create the different species) and has sleeping accommodations on board. There are hotels on the islands, but staying in one defeats the purpose of the visit—it’s essential to get out and about to see what Darwin saw. The islands are also a great place for diving and snorkeling.

The largest settlement on the islands is on Isla Santa Cruz; here you can visit the Charles Darwin Research Station, where many of the islands’ species of tortoise are looked after and studied. One tortoise, nicknamed Lonesome George (see Figure 6-2), is thought to be up to 90 years old. Unfortunately, he is the last known Pinta giant tortoise (he weighs 88 kilograms and is a meter across) and has failed to mate with younger females of similar species. Also on Isla Santa Cruz is the El Chato Tortoise Reserve, where it’s possible to see many giant tortoises in one place.

Figure 6-1. Lonesome George; courtesy Oliver Lee (o spot)

Any Galápagos tour should include a visit to Isla Fernandina for its colony of marine iguanas, Isla Bartolomé for its barren landscape and the hike up the now-dormant volcano, and Isla Espanola for the variety of wildlife (including a large colony of sea lions).

Practical Information

General information about the Galápagos National Park is available from http://www.galapagospark.org/. Many tour operators offer tours around the islands. Ecoventura (http://www.ecoventura.com/) offers carbon-neutral, English-speaking tours that last seven nights and include all the major sights and snorkeling.

Information about the Charles Darwin Research Station can be found at http://www.darwinfoundation.org/.

Artificial Speciation

Geographic isolation is one of the major ways in which a single species can split into two. If a species, such as Darwin’s finches, becomes separated into two groups isolated by some geographical feature (such as mountains or oceans), it’s possible for allopatric speciation to occur—the two groups evolve in different ways in accordance with their environment.

Going beyond the evidence of existing species, experiments have been performed to test the theory of allopatric speciation, deliberately splitting a population in two and exposing the two groups to different environments. After a number of generations, the evolution of the two groups has often diverged enough that they are no longer interested in mating with one another. Scientists often use fruit flies for artificial speciation experiments.

Fruit flies are a favorite tool of biologists because they have a short lifespan, are easily cultured in laboratories, and are readily available. The 1933 Nobel Prize in Medicine was awarded to the American scientist Thomas Hunt Morgan for the discovery that chromosomes (long, single pieces of DNA) carried the genes responsible for the inheritance of traits. He used the fruit fly Drosophila melanogaster, and its many mutations, to confirm his theory.

Figure 6-2. Dodd’s artificial speciation experiment

In 1989, Diane Dodd (of Yale University’s Department of Biology) reported on an experiment using Drosophila pseudoobscura (a species of fruit fly). This experiment involved taking a population of fruit flies and splitting it into two isolated groups (see Figure 6-1). One group was fed a diet of maltose; the other was fed a diet of starch. The experiment was repeated with an additional three populations, each split into the same two groups with the same maltose or starch diet.

The separate groups were allowed to feed, reproduce, and die for about one year. The flies were then bred for a single generation, all feeding on the same mixture of cornmeal, molasses, and agar. They were then given the opportunity to mate with one another in a series of tests that mixed originally maltose-fed and starch-fed males with samples of either maltose-fed or starch-fed females.

The experiment showed that the two populations had become behaviorally isolated—they would only mate with flies that had come from a population fed with the same food. Thus, isolation because of geography, which could lead to different food supplies being available, could result in populations that would no longer breed together.