A narrower definition specifies the requirement for irreversibly distinct behavioral groups or castes ( with respect to sterility and\/or other features ) . The newer definition excludes all social vertebrates ( including mole rats ) , because they do not have distinct castes that are different . A narrower definition specifies the requirement for irreversibly distinct behavioral groups or castes ( with respect to sterility and\/or other features ) , and such a definition excludes all social vertebrates ( including mole rats ) , none of which have irreversible castes .