Classification should be based upon anatomical characteristics that arose due to common descent, whether those common features be in the skeleton, skull, soft tissues, teeth, genetic structure or wherever. That being so, the objective of classification in the reconstruction of parts -as far as possible- of the evolutionary history that led up to the organisms under consideration. In short, good classification is based upon evolution. Classification involves grouping of organism into a formal system based on similarities in internal and external structure or evolutionary history. Two species are more closely related if they have more characteristics in common. And if two species are more closely related, then it means they have a more recent ancestor. For example, in a family, a brother and sister are closely related and they have a recent common ancestor i.e., their parents. A brother and his cousin are also related but less than the sister and her brother. This is because the brother and his cousin have a common ancestor i.e., their grandparents in the second generation whereas the parents were from the first generation. With subsequent generations, the variations make organisms more different than their ancestors. This discussion clearly proves that we classify organisms according to their resemblance which is similar to creating an evolutionary tree.