Evolution means the gradual and slow change in the body design of an organism . Evolutionary relationship are traced in the classification of organism. Classification of organism is based on how closely two species are related and how much characteristics they have in common . For classification , we look for similarity among the organism which allow us to group them . If species have more characteristics in similar , then more closely they are related . It indicates that they are recently evolved and more recently they would have had a common ancestor. Thus, classification of species is in fact a reflection of their evolutionary relationship