In most respects, humans are one of a relatively small number of species that evolved a very different strategy of investing more energy to reproduce more slowly. Like apes and elephants, we mature at a leisurely pace, grow large bodies, and have few babies but devote much time and energy to raising them well. This unusual strategy succeeds because while apes and elephants produce fewer babies than mice, a larger percentage of their offspring survive to then reproduce. A house mouse can become a mother when she is just five weeks old, has four to ten pups per litter, and can have a new litter every two months over the course of her approximately twelve-month life. However, the vast majority of her pups die young. In contrast, a chimp or elephant mother does not reproduce until she is at least twelve years old, and she gives birth to only one infant every five or six years over the next thirty or so years. About half of these offspring make it to becoming parents.