Ten thousand years ago, when humans first invented agriculture, there were maybe one million humans on the planet. By about the 1300s, when the Black Death appeared, there were about 400 million. We didn’t reach a billion until the year 1800; in the late 1920s we passed the two billion mark and by 1960 we passed three billion. In 2018 there are 7.6 billion people (the world population clock gives a running total.
