a whale is a kind of mammal & a cat is a kind of mammal ->  a cat and a whale are both mammals  a cat and a whale are both mammals & mammal is a kind of class of animal ->  a cat and a whale are part of the same class of animals  an animal is a kind of living thing & living things in the same class are more closely related than living things in different classes ->  animals in the same class are more closely related than animals in different classes  a cat and a whale are part of the same class of animals & animals in the same class are more closely related than animals in different classes -> a cat is more closely related to a whale than to animals of a different class