Charles Darwin was born on the 12 February 1809, in Shrewsbury. He is probably most famous for his theory of Evolution. Darwin travelled across the world on a ship called the Beagle as a naturalist. He visited many exotic places including South America the Galapagos Islands. In South America he found fossils of extinct animals that were similar to modern species. On the Galapagos Islands he found many species of animal that were similar to the species of the fossils and modern day species and species on different continents but were different in slight ways. He also found that there were a number of different types of finch on the different islands of the Galapagos, differing in things like colour, beak size and length.
Darwin returned to England in 1839. He studied his finding and eventually came to a conclusion. Darwin believed that species could change over time by a means that he named natural selection. This, put simply, means that if an organism is not suited to its environment it is less likely to survive and produce offspring, while the better suited organisms will survive and produce offspring, thus passing on the characteristics which helped them survive onto their offspring. This causes the species to gradually evolve over time. In the example of the Galapagos finches, each type of finch had adapted to the needs of the different environments of the different islands. Some had shorter harder beaks which helped them open seed pods, while others were coloured in a way that would camouflage them against the flora and landscape of their island.
Darwin did not want to publish his theory because he did not have an explanation for the process that creates the variance in the first place, he also anticipated that many people would not like the implications of his theory. The process evolution relies on is genetic mutation to allow differences to develop. Little was known about genetics at the time and DNA was only discovered over 100 years later. He eventually published his theory in his book 'The Origin of Species by means of Natural Selection' (1859).