Darwin was a scientist who came up with the theory of natural selection. Darwin first saw this when he went to the Galapagos Islands. He saw that a birds from the islands all looked alike, but had slightly differences depending on what island they lived. Darwin learned that the birds were in fact related. The Finches at one point all came from the same ancestor. The finches had to change or grow different beaks to eat the food that were located on their island.
Another species that was observed by Darwin was he tortoises that lived on the Galapagos Islands. They were very similar to the mainland tortoises. The tortoises that had grass to eat were different from the ones who had to eat cacti. The ones that had to eat cacti had longer extended legs and more room at the head/neck area to eat the leaves at the top of the cactus.
A few years later J. W. Tutt was a moth collector and was curious as to why only certain ones survived in certain conditions. He came up with a theory that darker ones would survive better in sooty trees because they would be able to hide from prey better. Years later a scientist named Bernard Kettlewell came up with a way to test his theory. He released moths into two different areas. After some time when by he looked to see how many survived from each area. Moths that matched their background survived better than the ones that did not.
Perry , J. (Writer) (2013). What is natural selection? [Web]. Retrieved from http://www.youtube.com/watch?v=0SCjhI86grU