Why do some species die out and others live on? © AMNH, Ross MacPhee   WHAT DIES OUT--AND WHY? An integral part of the ebb and flow of life on earth, extinction is the disappearance of an entire species. It’s clear that over the course of life on earth many more species have died out than exist at present. When an extinction happens, not only is the physical organism itself lost—along with it its camouflage, mating dance, fragrance or fur—so is its unique genetic code. “Thus, when the last individual of a species dies, what also disappears are the unique aspects of its genetic endowment,” explains Ross MacPhee, chairman of the Department of Mammalogy at the American Museum of Natural History.      1 of 17