The method of arranging organisms into groups on the basis of similarities and differences is called classification. Evolution on the other hand refers to a slow, gradual and continuous process by which the previously existing organisms develop into existing living organisms.All living things are identified and categorised on the basis of their body design in form and function. Once a certain body design comes into existence, it will shape the effects of all other subsequent design changes, simply because it already exists. So, characteristics that came into existence earlier are likely to be more basic than characteristics that have come to existence later. This means that the classification of life forms is closely related to their evolution.