text: It all depends on the needs of the animal or species, as well as energy usage.  Prey items such as mice or rabbits put a lot of energy into producing several babies frequently, with less time spent raising them (a month as opposed to a year or more).  This is because they need to keep the population booming, as there is a high mortality rate due to predation.  On the other hand, predators, such as big cats, or larger animals that don't have predators, such as elephants, put less energy into biologically developing a lot of babies, and put more time and energy into raising the few that they have, to ensure that the young are ready/fit to survive.  It's a quantity versus quality issue.  Animals have a limited amount of energy they can devote to reproduction, so they have to make a "choice."  It can't be both.