In which John Green teaches you about population. So, how many people can reasonably live on the Earth? Thomas Malthus got it totally wrong in the 19th century, but for some reason, he keeps coming up when we talk about population. In 1800, the human population of the Earth passed 1 billion, and Thomas Malthus posited that growth had hit its ceiling, and the population would level off and stop growing. He was totally right. Just kidding, he was totally wrong! There are like 7 billion people on the planet now! John will teach a little about how Malthus made his calculations, and explain how Malthus came up with the wrong answer. As is often the case, it has to do with making projections based on faulty assumptions. Man, people do that a lot.