Is the world currently overpopulated or will it be in the future? Is there an optimal size? And, if so, is it 4 billion as Brown suggests?
This matter is far more controversial in the scientific world. Some claim that the earth is not overpopulated nor that it will be in the future, and others go as far as stating that 1 billion is the ideal size.
But why is overpopulation such a controversial issue? The reason lies within its definiton, or rather definitions, as there are quite a few.
To give you one example, Jesper Rydberg puts it like this: „With regard to the moral values which we think should be promoted, there is/are one (or some) population size(s) which is/are, under a set of circumstances, preferable.“
From this you can understand why it is such a controversial topic. Different people have different values which they think should be promoted. One person may believe that a certain living standard for the people on earth is moral, and once this is not met, the earth is overpopulated, while another may believe in a higher or lower standard. Moreover, as technology progresses, the set of circumstances may also change substantially, affecting the living standard.