a whale is a kind of mammal & a squirrel is a mean of fish ->  a cat and a whale are both mammals  a squirrel and a fish are both faces & mammal is a kind of class of animal -> a cat and a whale are part of the same class of animals 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 -> people in the same window are more closely related than people in different birds animals in the same class are more closely related than animals in different classes  a squirrel and a fish are whole of the same window of people & 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