The world was already changing when Charles Darwin was born. Steam-powered engines were replacing waterwheels, sails, and muscle power, cloth was being made in factories instead of cottages, and the first steamboat had paddled its way up the Hudson. Farm laborers were abandoning the countryside and moving into the cities in search of better wages. And new scientific discoveries were overturning old ideas about the way the natural world really worked. Three ideas in particular, each developed only a few years before Darwin’s birth, would play a significant role in his thinking as he made observations during his voyage on the Beagle, and in the decades that followed as he outlined his theory of evolution by natural selection.
1. Extinction is Real.
By the beginning of the 18th century, naturalists had established that fossils were the remains of ancient animals and plants rather than simply strange-shaped rocks, but they refused to believe that they were the remains of organisms that were no longer alive anywhere on the planet. They thought it was illogical for God to have created animals only to destroy them again, so they assumed that fossils were the remains of organisms that had migrated somewhere else, so they were no longer around in that location. But a few years before Darwin’s birth, the French anatomist Georges Cuvier established that many of the large mammal fossils that were getting dug up in Europe and the Americas were the remains of unique species with no living members. There were no living Irish elk, no giant ground sloths, and no American mastodons. The reasons for their disappearances were unknown, but it was clear that species could and did vanish forever.
2. The Earth is Old.
By 1809 natural philosophers were becoming convinced that the Earth was far older than the Bible suggested. Its actual age was still disputed (and would be for more than a century): a set of modeling experiments in 1779 led the Comte du Buffon to estimate that the Earth was 75,000 years old; by 1795, James Hutton’s geological observations had convinced him that the planet was much, much older – with “no vestige of a beginning, no prospect of an end.” So Darwin was born into a world that was considered old, and with new estimates was steadily getting older. There had been more than enough time for living things to change form.
3. Populations can Outstrip their Resources
Thomas Malthus didn’t think much of utopian thinkers like Rousseau. Rousseau and his followers held that people were naturally good and were only taught greed and war by civilization. In response, Malthus set out to demonstrate that there was no way people could abandon war and live in harmony. Laying out his thesis in An Essay on the Principle of Population (1798), Malthus suggested that prosperous countries will always outbreed their capacity to feed their population, and the only reason the planet hadn’t already been overrun with people was because plagues, infanticide, war, and late marriage forced by poverty kept the human population in check. When Darwin read the Essay decades later, he realized that what Malthus suggested for humans could also be applied to any organism on Earth. It gave him the mechanism he needed to explain how living things could change over time – when there are too many individuals for an environment to support, the ones that could best survive in that environment would leave the most offspring. He later wrote: “…being well prepared to appreciate the struggle for existence which everywhere goes on from long-continued observation of the habits of animals and plants, it at once struck me that under these circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The results of this would be the formation of a new species. Here, then I had at last got a theory by which to work".