“‘It has never happened!’ cannot be construed to mean, ‘It can never happen!’– might as well say, ‘Because I have never broken my leg, my leg is unbreakable,’ or ‘Because I’ve never died, I am immortal.’ One thinks first of some great plague of insects – locusts or grasshoppers – when the species suddenly increases out of all proportion, and then just as dramatically sinks to a tiny fraction of what it has recently been. The higher animals also fluctuate.
During most of the nineteenth century the African buffalo was a common creature on the veldt. It was a powerful beast with few natural enemies, and if its census could have been taken by decades, it would have proved to be increasing steadily. Then toward the century’s end it reached its climax, and was suddenly struck by a plaque of rinderpest. Afterwards the buffalo was almost a curiosity, extinct in many parts of its range. In the last fifty years it has again slowly built up its numbers.
As for man, there is little reason to think that he can, in the long run, escape the fate of other creatures, and if there is a biological law of flux and reflux, his situation is now a highly perilous one. During ten thousand years his numbers have been on the upgrade in spite of wars, pestilence, and famines. This increase in population has become more and more rapid. Biologically, man has for too long a time been rolling an uninterrupted run of sevens.” – George R. Stewart, Earth Abides