In 1837, at the age of 28, Darwin wrote "Species Change" in one of his notebooks, which was the earliest record of his evolutionary ideas. Prior to this, he had sailed around the world for 5 years on the HMS Beagle, observing numerous signs that species were not fixed in South America, Oceania, and other places. After returning to England, he wrote "cuidado" (meaning "be careful" in Spanish) in another notebook, realizing that the theory of evolution was a radical and dangerous view, and that there was insufficient evidence to make it public at that time.

Over the next 20 years, Darwin continuously accumulated a vast amount of data and first presented his views to a small circle of scientists. It was not until 1859, when "On the Origin of Species" was published, that his ideas became accessible to the general readership, causing a great sensation. The first edition of 1,250 copies sold out on the day of publication, and the circulation reached 4,250 copies within a year, receiving both praise from the scientific community and fierce criticism from the religious community and conservative forces.

To this day, "On the Origin of Species" remains one of the most important works in human history, and one of the few works that still has scientific value more than 150 years after its publication. Darwin was well aware that his work was only the beginning. He wrote in the book: "In the distant future, I see open fields for far more important research."