the theory of evolution came from charles darwin. he was an explorer who went to the galapagos islands and saw that the birds there were different from the ones in South America! he came up with some theories of how this may have taken place. now we recognize them as the theories of evolution! 
the main four are comparative anatomy, DNA, geographical distribution and fossils!

helpful terms 

natural selection- when organisms have the genes needed to survive and can reproduce giving the genes to their children. "survival of the fittest"

comparative anatomy- study of similar/different body parts in life
  • homologous- similar parts that came from a common ancestor
  • analogous- parts that serve the same purpose but not from same ancestor
  • vestigial- parts that no longer have or reduced function
  • embryos- common features that are seen at, before or after birth that means common ancestor. 

geographical distribution- why certain species live where they do