Friday, July 22, 2016

Charles Darwin and the Galápagos Islands

The Galápagos Islands are located 620 miles (1,000 kilometers) from the South American mainland but a world apart from anywhere else on Earth. 

The archipelago and its surrounding waters, located where three ocean currents converge, are famed for the unique animal species that piqued the interest of Charles Darwin in 1835. 

Decades later Darwin drew on his experiences here when penning his landmark "Theory of Evolution by Natural Selection."

On Sept 15, 1835 a British Naval Ship arrived at the eastern edge of the Galápagos. The HMS Beagle had spent the last 3 years surveying the coast of South America. The crew produced an updated map of the remote island chain that came to be known as the Galápagos Islands.

On board the ship was the 26-year-old theology student and budding scientist Charles Darwin, who would change the course of history. As the ship's 'Naturalist', Darwin's job was to collect plant and animal specimens from the islands. He became fascinated with their geology. Like many scientist of his day, Darwin no longer accepted, as literal, the Bible's account of the creation of the Earth. He questioned the traditional view of the natural world as permanent and unchanging.

In the Galápagos, Darwin saw evidence of change all around. He had heard reports that the islands were daunted with volcanoes, now he began to understand their power.

He marveled at the vast craters and the endless lava fields sharp as glass. The flows looked as if they had cooled only yesterday. Darwin could see that volcanic eruptions continually reshaped the islands. This fueled his growing conviction that the entire planet is in flux, shaped by monumental forces like volcanoes and erosion. He also recognized the power of earthquakes as he had witnessed and lived through one during a stop-over in South America.

Darwin was the first scientist to claim that volcanoes had created the Galápagos. He had grasped the fundamental nature of the islands, just not the fundamental details, such as the hotspot that fuels the volcanoes. He was not aware of 'Plate Tectonics', that the ocean floor slides across the hotspot and carries the islands to the east.

As the Beagle moved methodically through its mapping survey, Darwin became convinced that the island chain was a little world within itself, worthy of his study. He surmised that the Galápagos emerged from the open sea, created by volcanoes. The profound implication is that the islands came first, life came later.

Where did life come from and why was life so different from one island to the next?

Darwin turned his attention from the islands craters and lava flows to the creatures living on them. The HMS Beagle spent 5 weeks mapping the Galápagos. Charles Darwin took every opportunity to go ashore and study island life. He explored from coastline to highland and discovered fresh water pools alive with birds. Darwin reasoned that the islands had been colonized by species of plants and animals from South America. But he was puzzled because he had been taught that species were fixed in nature, created by God. He believed that species could not change into something entirely new; but he had to believe his eyes!

The plants and animals from the Galápagos were not identical to those on the mainland. It was as if they had been transformed since their arrival on the islands. Darwin spent decades making sense of his observations. For the time being, "he collected plant, insect and animal specimens by the trunk-full."

The Governor of one of the islands was away, so the Vice-Governor went down to the ship to greet him and the rest of the crew. The Vice-Governor’s name was Nicholas Oliver Lawson. Lawson informed Darwin that he could tell which island the large tortoises came from by the distinctive markings on its shell.

Darwin didn't realize it at the time, but giant tortoises are one of the strongest examples of evolution in the Galápagos. Their ancestors were small bodied tortoises that arrived millions of years ago and may have colonized islands that have since sunk beneath the waves.

Geologist and Scientist are not sure how they became giants. Possibly because of a lack of competition for food, or because they had no predators to hide from. Over millions of years giant tortoises reproduced in different habitats across the Galápagos. They produced countless offspring, but only the fittest survived. In each habitat, natural selection favored certain individual's over others. Each survivor passed on its characteristics to its offspring. Over time more than a dozen distinct races of tortoises evolved across the islands.

Different islands, different conditions, different tortoises, is a striking illustration of evolution.

Galápagos Finches

The Galápagos Islands are home to a famous group of birds called "Darwin's finches." Most taxonomists view these finches as belonging to thirteen separate species within four (or three) genera of a single family (or subfamily). All of the Galápagos finches are thought to have descended from one or a few pairs of ancestral birds that strayed from the South American mainland.

Collected by Charles Darwin during his Beagle voyage, these finches have long been featured as significant examples of evolution. They are typically exhibited as a notable instance of "adaptive radiation," which is defined as the relatively rapid production of a number of new species from a small ancestral population expanding into unoccupied niches, especially thought to occur on isolated islands.

As a result of the diligent and extensive field work of Peter and Rosemary Grant of Princeton University, "Darwin's finches" have become more important than ever as proof that evolution happens. Jonathan Weiner's well-written book "The Beak of the Finch" won the 1994 Pulitzer Prize for non-fiction, and brought to public attention the probable confirmation of Darwinian evolution.





 



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