Demographic

Population has not been constant or steady over the long sweep of time.

The tool-using and tool-making revolution kicked off the rapid rise in population around 1 million B.C.E. The aid of various implements "gave the food gather and hunter access to the widest range of environments." But when the productivity gains from the use of primitive tools had been exploited, the rate of population growth fell, and population size again settled down near a plateau.

The next rapid jump in population started perhaps ten thousand years ago, when people began to keep herds and cultivate the earth, rather than simply foraging for wild plants and game.

These two facts imply that the present rapid population growth, starting 300 or 350 yrs ago, may abate when the benefits of the new industrial and agricultural and other technical knowledge that followed the early scientific and industrial revolutions begin to peter out.

In the long-run view population size adjusts to productive conditions rather than being an uncontrolled monster. Constant geometric growth does not characterize human population history. Population growth to some extent represents economic success and human triumph, rather than social failure. 

Population size and growth are influenced by political and economic and cultural forces, and not only by starvation and plague due to changes in natural conditions.

The main cause of the rapid increase in population during the past two centuries is the decrease in the world's population rate.