We are frequently reminded about the seemnigly unending growth of the world's population. Some people like to make statements such as: 'Our planet can't feed 10, 15, 20 billion people!' and therefore changes have to be made.
I personally don't agree with such statements cause I am positive that few people in the past, when the population was around 1 billion, believed that 7 billion of us could live and survive on planet Earth.
Now what I want to know is how many people did the 18th, 19th or 20th century scientists, politicians think our planet could hold?
The last word in human population dynamics from 1800 to ca. 1965 was Thomas Robert Malthus. While Malthus didn't really give precise numbers, malthusian theory was fairly good at explaining population as a balance between fertility rates and the basic ability of the land to produce agriculture.
I'm not sure I would currently consider malthusian principles no longer active, but the huge technical leap in the 1960s in both the realm of fertilizers and in the invention of dwarf wheat by Norman Borlaug drastically increased our ability to produce food. Until the invention of dwarf wheat, India could not consistently feed itself, for example.