During the last Ice Age, large, hairy elephants roamed Asia and the Americas. But by about 4,000 years ago, all the mammoths and mastodons had vanished.

Could these ancient beasts ever come back to life?

A Special Sheep

Normally, to make a new baby animal, it takes two parent animals of the same species. Baby animals get half of their DNA from Mom and half from Dad. When these two halves join up inside a fertilized egg, a baby starts to