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• Charles Darwin was an English naturalist who studied variation in plants, animals and fossils.
• Darwin is perhaps most famous for his work on the theory of evolution, which challenged many religious beliefs about creation.
• He wrote several texts outlining his scientific theories, including books called On the Origin of Species in 1859 and The Descent of Man in 1871.

Charles Darwin was born in Shropshire, England in 1809. In 1825 he went to the University of Edinburgh to study medicine.

His experience at university provided him with a wide scientific education. He was exposed to new, and sometimes controversial, scientific ideas and theories in debates, talks and through student societies. However, he did not enjoy certain parts of his studies, particularly the study of anatomy and surgery.

He left Edinburgh after two years and started studying for a degree at Christ College, Cambridge, working towards becoming a member of the clergy on the advice of his father.

While studying, Darwin developed an interest in nature and how religious ideas and nature were linked. He became good friends with John Stevens Henslow, who was a professor at Cambridge University.

After completing his studies, Darwin received a letter in 1831 from John Stevens Henslow inviting him to go on a voyage on the HMS Beagle. Henslow thought of Darwin when the ship’s captain, Fitzroy, told him he was looking for a naturalist to join him on the journey. Henslow, who had got to know Darwin well at Cambridge, knew Darwin would be interested. Darwin joined the expedition, which lasted for nearly 5 years.

In September 1835, the Beagle arrived in the Galapagos Islands, 600 miles from Ecuador. Darwin made detailed notes and collected lots of animals, plants, insects and reptiles. He noted that the shells of tortoises differed from island to island, and there were differences between the finches (a type of bird), as the shape of their beaks varied.

When he returned to England, Darwin shared many of the specimens and research from his travels with other biologists and researchers. Over time, he came to think that the animals he had seen on his travels had adapted to the environment that they lived in.

Darwin had made careful notes as the voyage went on, later publishing these in a collection he called Journal of Researches. This was later renamed Voyage of the Beagle. He revised his ideas over several years and published several updated editions of the book.

He came to believe that although the different islands had similar plants and animals, many seemed to have changed - or adapted - to suit the local environment. Finches, for example, had different beaks on each island, and he thought their beaks had adapted according to the food they ate. He frequently discussed his ideas with other researchers, such as Charles Lyell, who was a prominent Scottish scientist.

Darwin was reluctant to publish his work on evolution for many years, despite his thoughts and the significant amount of work he had done on the adaptations between different species. This was because:

• He wanted to make sure he had enough examples and evidence to support his theory.
• He was aware that some of his ideas contradicted the creation story in the Old Testament.
• He suffered from ill health and spent time grieving the death of his daughter, Annie.

In 1856, a biologist called Alfred Russel Wallace wrote to Darwin. He had many similar ideas about natural selection and wanted to share his thoughts. Charles Lyall warned Darwin that if he did not share his work then he would risk not getting any credit for his ideas. This prompted Darwin to publish his work. Wallace and Darwin had some of their thoughts on natural selection jointly published in a journal in 1858.

Darwin’s most well-known work, On the Origin of Species, was published in November 1859. In the book, Darwin set out his theory of evolution, based on his years of research and what he had seen when travelling across the globe on the Beagle.

• Darwin saw that when an animal adapted successfully to its environment, it thrived.
• Darwin realised that when an animal was more suited to the environment it lived in, it would be more successful at surviving in that climate so it would thrive and breed.
• This successful adaptation then resulted in that species becoming the dominant, or most common, variety. He called this idea natural selection, when different species of animals evolved over many generations.
• He used a wide range of examples of animals he had seen on his travels to support his claims, such as thrushes, ants and cuckoos.

Darwin wrote The Descent of Man in 1871. In this work he set out his theory that humans had evolved from apes. This was seen by many as a direct contradiction to the creation story as stated in the book of Genesis in the Old Testament. By this time some people did not view the creation story as a literal story on how the world was made, but some people did.

Darwin recognised that his theory could offend some people, writing in his book’s concluding remarks;

The main conclusion arrived at in this work, namely that man is descended from some lowly-organised form, will, I regret to think, be highly distasteful to many persons.

Even before the publication of The Descent of Man, Darwin’s work was discussed at a debate held at the Natural History Museum in 1860. Darwin’s work was debated by the Bishop Wilberforce of Oxford (arguing against Darwin’s ideas) and Thomas Huxley (a biologist supporting Darwin).