8.2–8.4: Darwin journeyed to a new idea.

The Galápagos land iguana, Conolophus subcristatus.

Charles Darwin grew up in an orderly world. In the Victorian British society he inhabited, many beliefs about humans and our place in the world had changed little over the previous two centuries. Biblical explanations were sufficient for most natural phenomena: most people thought the earth was about 6,000 years old. And with the occasional exception of a flood or earthquake or volcanic eruption, the earth was believed to be mostly unchanging. People recognized that organisms existed in groups called species or kinds. (In Chapter 10, we discuss in more detail what a species is; for now, we’ll just say that individual organisms in a given species can interbreed with each other but not with members of another species.) People in Darwin’s society also generally believed that all species, including humans, had been created at the same time and that, once created, they never changed and never died out.

Darwin threw into question some long- and dearly held beliefs about the natural world, and he forever changed our perspective on the origins of humans and our relationship to all other species. He didn’t smash his society’s worldview to pieces all at once, though, and he didn’t do it by himself (FIGURE 8-3).

Figure 8.3: Scientists who shaped Darwin’s thinking.

In the 1700s and 1800s, scientific thought was advancing at a rapid pace. In 1778, the respected French naturalist Georges-Louis Leclerc, Comte de Buffon shook things up by suggesting that the earth must be about 75,000 years old. He arrived at this age by estimating that 75,000 years was the minimum time required for the planet to cool from a molten state. In the 1790s, Georges Cuvier began to explore the bottoms of coal and slate mines and found fossil remains that were unlike any living species. Many interpreted the Bible in such a way that made Cuvier’s discoveries unthinkable, believing that biblical accounts did not allow for species to be wiped out. Cuvier’s publications documented giant fossils (including the Irish elk, the mastodon, and the giant ground sloth) that bore no resemblance to any currently living animals (FIGURE 8-4). And although Cuvier was not a proponent of the idea of evolution, the fossils he discovered allowed only one explanation: extinction was a fact. Troubling as this observation was for the prevailing Western worldview, it was only the beginning.

Figure 8.4: Extinction occurs. Deep in coal mines, Cuvier discovered the fossilized remains of very large animals no longer found on earth.

Not only was it starting to seem that species could disappear from the face of the earth, but several scientists, including Darwin’s own grandfather, Erasmus Darwin, began to suggest that living species might change over time. And in the early 1800s, the biologist Jean-Baptiste Lamarck championed a popular idea about the mechanisms by which this change might occur. The idea—that change came about chiefly through organisms’ use or disuse of particular features—was wrong, but the increased willingness among scientists to question previously sacred “truths” contributed to an atmosphere of unfettered scientific thought in which it was possible to challenge convention.

Perhaps the revolutionary ideas that most inspired Darwin were those of the geologist Charles Lyell. In his 1830 book Principles of Geology, Lyell argued that geological forces had shaped the earth and were continuing to do so, producing mountains and valleys, cliffs and canyons, through gradual but relentless change. This idea that the physical features of the earth were constantly changing would most closely parallel Darwin’s idea that the living species of the earth, too, were gradually—but constantly—changing.