Milk is milk, right? Mammals make it (humans are mammals) and babies drink it. There's more to the story than that. Each species of mammal makes a unique kind of milk, which meets all the nutritional requirements of its offspring at the beginning of life. Each species' milk has specific qualities that insure the survival of the young in a particular environment. This principle is known as the biological specificity of milk. Mother seals, for example, make a high-fat ...