"The elephant is reckoned to be the slowest breeder of all known animals, and I have taken some pains to estimate its probable minimum rate of natural increase: it will be under the mark to assume that it breeds when thirty years old, and goes on breeding till ninety years old, bringing forth three pairs of young at this interval; if this be so, at the end of the fifth century there would be alive fifteen million elephants, descended from the first pair."
The Origin of Species - Charles Darwin
Wow, long winded n c'est pas? Anyway, for anyone that needs the context, he's talking about how different conditions, both favourable and disfavourable bring about the impossibility of simple, mathematical, calculation of the species in questions development periods. Or something like that, its not really an enthralling read *shrug*