The fifth revolution will come when we have spent the stores of coal and oil that have been accumulating in the earth during hundreds of millions of years … it is obvious that there will be a very great difference in ways of life … a man has to alter his way of life considerably, when, after living for years on his capital, he suddenly finds he has to earn any money he wants to spend … This change may justly be called a revolution, but it differs from all the preceding ones in that there is no likelihood of its leading to increases of population, but even perhaps to the reverse.

Charles Galton Darwin, 1953, p. 52