Charles Darwin, was a naturalist from Britain, who published the book "On the Origin of Species". He sailed around the world on the HMS Beagle and made some important observations about species in the Galapagos Islands. 

One example of Darwin's observations are those he made about tortoises in the Galapagos Islands. He noticed that the tortoises on different islands, with different environments had physical differences. 

Go to the Bite Size page on Charles Darwin, and read this page about his work. Then watch the Brightstorm video below, Darwin's Theory of Evolution