3.2: The Journey to Natural Selection

Who Was Charles Darwin?

It’s worth pausing on Darwin as a person before turning to Darwin the scientist because the two are hard to separate. Born in 1809 into a wealthy, well-connected English family, Darwin was, by his own account, an unremarkable student. He found medical school in Edinburgh unbearable and drifted through divinity studies at Cambridge with little enthusiasm. What he loved doing most of all was collecting beetles, hunting, and taking long walks in the countryside. He wasn’t the era’s brightest young star; he was something rarer—someone capable of sustained, patient curiosity, comfortable sitting with a question for decades rather than rushing to an answer.

It also matters that Darwin didn’t invent the idea of evolution. By his time, as we’ve seen, it had already been circulating for millennia across multiple civilizations. What set Darwin apart was his ability to synthesize an overwhelming range of evidence, from geology to economics to pigeon breeding, into a single coherent explanation, and his willingness to keep testing that explanation against every new observation he could get his hands on for the rest of his life (Harel 2022; Sumner 2010).

Five Years at Sea (Mostly on Land)

In 1831, at age 22, Darwin joined the crew of the HMS Beagle as it set out to chart the coastline of South America. Darwin suffered from severe seasickness the entire voyage, so severe that of the nearly five years the expedition lasted, he spent only about a year and a half actually aboard the ship (Costa 2017). The rest of the time, he was ashore, and that turned out to be a scientific gift: it gave him unmatched time to explore, collect, and observe.

In Argentina, Darwin found fossils of extinct armadillos in the very same locations where living armadillos still roamed — a direct challenge to Cuvier’s catastrophism, which held that extinct and living forms must be entirely separate species from separate creation events. Traveling along the South American coast, he also noticed that closely related species varied gradually from place to place, with populations that lived closer together looking more alike than those farther apart.

These patterns became unmistakable in the Galapagos Islands. Local residents told Darwin they could identify which island a giant tortoise came from just by looking at the shape of its shell. Darwin noticed the same island-by-island variation among the islands’ finches. Something was clearly happening here that the fixed, unchanging categories of the time couldn’t explain.

Twenty Quiet Years at Down House

Darwin knew exactly how risky these ideas were. Lamarck had been discredited and harassed for his theory of species change. Even Charles Lyell, Darwin’s close friend, rejected the idea that species could change at all. So instead of rushing into print, Darwin spent roughly two decades after returning to England quietly gathering evidence at Down House, his family home for over forty years.

Down House essentially became a working laboratory. At various points, the hallways held trays of frog eggs, sixteen breeds of pigeons cooed in the yard, jars of seeds floated in saltwater in the cellar, and the smell of dissected pigeon skeletons filled the air. Darwin even recruited his son William to help him test whether plant seeds could survive an ocean crossing. They filled a bathtub with salt water, dropped in seeds of different plants, and checked every day to see which ones stayed afloat, and whether the ones that sank could still sprout, which, remarkably, most could (Sumner 2010). It’s a small, homemade experiment, but it’s a perfect example of how Darwin worked: turning a genuinely testable question — in this case, how plants and animals might have colonized remote islands separated from the mainland by vast stretches of ocean — into a hands-on experiment, using whatever was on hand.

This picture of Darwin’s patient, methodical approach is worth sitting with, because it’s easy to imagine scientific discovery as a single lightning-bolt moment — a flash of genius, all at once. Darwin’s breakthrough looked nothing like that. It looked like decades of repetitive observation with one small notice adding to the next, until a pattern the size of a theory finally came into view. That kind of noticing isn’t reserved for scientists. Anyone can watch which weeds continue to pop up after being mowed and which don’t or which birds get the feeder first and which get pushed aside. The raw material of science is often just about paying attention long enough, and closely enough, to see what was there all along.

Did You Know? How One Species Becomes Many

Kauaʻi was formed by a volcano roughly five million years ago. As the oldest of the main Hawaiian Islands, it has had the most time to accumulate stray seeds carried in by wind, water, and animals — the same kind of long-distance colonization Darwin tested with his floating seed experiment at Down House. Whenever a new seed took root in the island’s soil, the resulting plant sometimes evolved into an entirely new species, or often several, each adapted to a different niche within Kauaʻi’s favorable climate. This process, in which a single ancestral species diversifies into many descendant species, is known as adaptive radiation and is the same phenomenon Darwin observed among the Galápagos finches. In Kauaʻi, the result has been thousands of plant varieties descended from just a handful of original colonizers, many of them endemic to the island, meaning they’re found nowhere else on Earth (Schlanger 2024:29).

The Letter That Changed the Timeline

Darwin might have continued gathering evidence indefinitely if not for a letter that arrived in June 1858 from Alfred Russel Wallace, a naturalist working independently in Malaysia. Wallace had arrived at strikingly similar conclusions and asked Darwin to review his paper and pass it along to their mutual colleagues Charles Lyell and Joseph Hooker. Rather than let Wallace publish alone, Lyell and Hooker arranged for a joint reading of both men’s work at the Linnean Society in England on July 1, 1858. Darwin’s own book, On the Origin of Species, followed fifteen months later in November 1859.