Statue of Charles Darwin at Natural History Museum

Each year on 12 February, Humanists and kindred freethinkers celebrate International Darwin Day. We do this in recognition of the paradigm changing contribution Charles Darwin (1809–82) made to human knowledge in his famous book, On the Origin of Species (1859). In it, he sets out how species can change naturally. Change, so they are better adapted to their environment, and change over time to evolve into new species. The idea that species could change was in stark contrast to the long-established religious claim that all species had stayed the same since ‘God put them on Earth’.

Mechanism for species change

How did Darwin come up with a mechanism for how species could change? From a young boy Darwin was a keen collector and observer of nature. So when, as a young man, he was offered a chance to travel on a scientific expedition around the world on the HMS Beagle, he said yes.  During this five-year voyage (1831–6) Darwin avidly collected specimens and made notes on the natural world, particularly in South America, the Pacific Islands and Australasia.  Upon returning to England, he married, settled down to raise a family and wrote up his observations in books and papers, while doing further research.

One set of observations that particularly intrigued him came from the Galapagos Islands.  He noticed that different populations of finches had different diets and different beak shapes; whereas on the nearby mainland of South America all finch populations looked the same and ate seeds. This led Darwin to ponder whether the differences he observed in the Galapagos finches might have arisen naturally.

With his knowledge of artificial selection, used by farmers to improve their livestock and crops by breeding from specimens with desired features, he realised that in nature something similar might be occurring. He called it ‘natural selection’.

Publishing on natural selection

Darwin wasn’t willing to rush into print on natural selection because he was aware that species change and evolution was a very controversial topic. It has been of interest to both scientists and the general public since.

So, while he worked on other projects, he kept collecting evidence that would support natural selection. He also discussed his ideas with his wife, who was a very committed Christian, and a few close scientific colleagues.

While Darwin continued to write up evidence for natural selection, two events had a significant effect on him publishing his ideas. One delayed his intent to publish, the second caused him to rush into print on natural selection.

The first arose when an anonymously authored book, Vestiges of the Natural History of Creation, appeared in 18441. It immediately made ideas about species change and life evolving ‘the hot’ topics for discussion in Victorian England.  Vestiges was a populist book that particularly appealed to freethinkers who had already rejected religion. However, most scientists of that time were very dismissive of the book; in part because they didn’t know who had written it and also because it contained many wrong and misleading claims. (The author did make corrections in subsequent editions.) Darwin was appalled by the sensational controversy this book was causing, so he continued to defer publishing his own version of species change.

The second event occurred in early 1858 when Darwin received a paper on species change from the other side of the world asking for his opinion on its suitability for publication. This paper by another naturalist, Alfred Wallace, outlined exactly what Darwin had been reluctant to publish on; namely species changing by natural selection.

If Darwin was to forward Wallace’s paper to a science journal, the honours on this important idea would go to Wallace. Luckily for Darwin, his colleagues, who knew he had been working on natural selection for some years, came up with a solution – two papers, one by Darwin, the other by Wallace, would be presented at the AGM of the Linnean Society on 1 July 1858. At the time, the papers made almost no impression on the scientific community, with the president of the Linnean Society commenting that no ground-breaking ideas had been presented in the past year!

While Wallace remained collecting specimens in the islands of SE Asia, Darwin sorted his extensive notes and turned them into a book, first published in November 1859, under the title On the Origin of Species by Means of Natural Selection. In it, Darwin went to great lengths to explain ‘natural selection’ as the mechanism by which species can adapt or form new species. He was using this term because it enabled him to compare natural selection with artificial selection, whereby humans selectively bred domesticated animals and plants to gain more desirable features. He also included chapters on fossil evidence and the similarities found in embryo development and body patterns specialized for different habitats.

Within a few years, Darwin’s Origins convinced most in the scientific community of his arguments. However, such was public interest in the more sensational book Vestiges it outsold Origins up until 1890 and even found a ready market into the twentieth century.


  1. The story of the public sensation caused by this book is covered in, Victorian Sensation: The Extra-ordinary Publication, Reception, and Secret Authorship of Vestiges of the Natural History of Creation, James A. Secord, University of Chicago Press, 2000.