Charles Darwin and Alfred Russel Wallace both developed the theory of evolution by natural selection. Darwin travelled around the world on the ship HMS Beagle and noticed that animals and plants on different islands, such as the Galapagos, were similar but had differences that suited each island. Wallace, working in Asia and the Malay archipelago, came to the same idea independently. In 1858 their ideas were presented together, and in 1859 Darwin published his book On the Origin of Species.
Their theory was controversial. Many people believed that each species had been created in its present form, and the theory conflicted with religious ideas. At the time nobody knew how characteristics were inherited. Genes and DNA were discovered later, and this gave the theory a mechanism, which strengthened the evidence for it.
The theory has had a huge impact on modern biology. It explains biodiversity, links all living things by common ancestry, and underpins classification. It helps us understand antibiotic resistance and why species become extinct. It also shows why genetic variation is valuable, so seedbanks store seeds from many species as a store of biodiversity. If the environment changes, the stored variation can be used to breed plants suited to new conditions.