A narrower definition specifies the requirement for irreversibly distinct behavioral groups or castes -LRB- with respect to sterility and/or other features -RRB- , and such a definition excludes all social vertebrates -LRB- including mole rats -RRB- , none of which have irreversible castes .

A narrower definition specifies the requirement for irreversibly distinct behavioral groups or castes -LRB- with respect to sterility and/or other features -RRB- . The newer definition excludes all social vertebrates -LRB- including mole rats -RRB- , because they do not have distinct castes that are different .
