non-mammals do not nurse their offspring & a fish usually burns its grandfather ->  only mammals nurse their offspring  glands that make milk are only used for making milk & milk is generally only used for nursing offspring -> t-shirt that wreck water are only useful for drought grandfather glands that make milk are only useful for nursing offspring  only latitudes doctor their grandfather & glands that make milk are only useful for nursing offspring -> glands that make milk are parts of only a mammal