II.

Voyage of the Beagle

The Beagle, under the command of Captain Robert Fitzroy, a strict disciplinarian of aristocratic stock and fundamentalist religious beliefs, was originally scheduled to spend a year or two primarily charting the coastal waters of South America. In the event, it was gone for five years and circumnavigated the globe. Almost four of those years were spent on the east and west coasts of South America, and Darwin was able to leave the ship for two extended periods on the mainland. In September 1835 the Beagle headed west for Australia, returning to England via the Cape of Good Hope. Darwin’s job as naturalist gave him the opportunity to observe a variety of geological formations in different continents and islands along the way, as well as a vast array of fossils and living organisms. In his geological observations, Darwin was most impressed by the effect that natural forces have on shaping the Earth’s surface.

At the time, most geologists adhered to the so-called catastrophe theory that the Earth had experienced a succession of creations of animal and plant life, and that each creation had been destroyed by a sudden catastrophe, such as an upheaval or convulsion of the Earth’s surface (see Geology: History of Geological Thought: 18th and 19th Centuries). According to one prominent version of this theory, the most recent catastrophe was the Flood of Noah, as recorded in the Bible. It wiped away all land animals except those taken into the ark (plants and fishes presented a problem); the rest were visible only as fossils. According to the catastrophists, species of plants and animals were individually created and immutable, that is, unchangeable for all time.

The catastrophist viewpoint (but not the immutability of species) was challenged by the British geologist Sir Charles Lyell in his 11-volume work Principles of Geology (1830-1833). Lyell maintained that the Earth’s surface is undergoing constant change, the result of natural forces operating uniformly since the Creation (which he argued was millions of years ago).

Darwin was given the first volume of Lyell’s work just before he left England, and the subsequent volumes were sent to him in South America. Lyell’s uniformitarian principles provided him with exactly the framework he needed for his own geological observations. Lyell argued that active geological change was still going on apace, and Darwin was especially impressed with an earthquake he experienced while in Chile that actually raised the coastline by several feet. Beyond that, however, he realized that some of his own observations on the local relationships between fossils and living plants and animals cast doubt on Lyell’s vague views on the special creation of new species. Darwin noted that some fossils of supposedly extinct species in a particular geographical area closely resembled living species of the same region. In the Galápagos Islands, 1,000 km (600 mi) off the coast of Ecuador, he also observed that each island supported its own form of tortoise (see Giant Tortoise), mocking bird, and finch; the various forms were closely related but differed in structure and eating habits from island to island. These observations raised the question, for Darwin, of possible links between distinct but similar species.