If each breeding pair of elephants produces 6 offspring during a 90-year life span, in 750 years, a single pair of elephants will have given rise to a population of 19 million elephants. Yet elephants have not overrun the planet. WHY?

I can think of several reasons

Explanation:

Not all the offspring will survive until they are old enough to propagate Disease and accidents will kill some mature individuals before they can produce six offspring Predators will kill the weak and infirm individuals Poachers will kill every elephant they can find for their valuable ivory The land has a limited carrying capacity. Each area has a limited amount of resources available, so the population will level off as it approaches this limit.