They are descended from ancestors who lived in burrows and had crepuscular activity, ie dawn and dusk, plus they ate a lot of animals and a lot of livers which are very rich in vitamin A. As a result they get health problems from too much vitamin D but need more Vitamin A than people do. We are descended from diurnal ancestors who got most of their calories from plant sources. Humans are the opposite of ferrets in relation to A and D so it is absolutely essential that people NEVER assume that they can postulate toxicity levels or need levels of these two nutrients from humans to ferrets. [Posted in FML 7105]