This graph shows the human population in millions (vertical axis) against the time in years (horizontal axis). The graph starts at fifteen thousand years before common era, with a very low population (close to zero on this scale). The graph is almost a straight line, sloping gently upwards, to about one thousand years in common era, by which time the population was about three hundred million. The graph then curves upwards, changing to a steeply rising straight line, so that by the year two thousand, the population is 5 thousand million.