The second consequence implies that intrinsic similarity is not necessary for membership of the same species. There exists a high degree of variation in intraspecific morphology and genetic makeup. While members of kinds need not be intrinsically identical (e.g., there may be isotopic variation between samples of a chemical element), there will nonetheless be certain distinctive intrinsic natural properties common to all members of the kind (e.g., nuclear charge in the case of atoms of the same