It is very difficult to fathom how evolution works and how a unicellular organism can turn into a complex living being like a Tiger or a Human. To help you learn the theory of evolution in an effective manner, we decided to go with an example of how an eye could have evolved from just a simple bacterium. Once you understand how a complex design can be formed by evolution by natural selection, you’ll be able to apply similar logic to explain other complex designs you find in nature.