The Next Million Years by Charles Galton Darwin discusses all the aspects of the problem of human survival for the next million years. In that long period of time, everything that can happen will have happened, including human extinction. Darwin makes the assumption that our species will somehow escape that grimiest of outcomes. He published the book in 1952 but wrote that he had considered the arguments for decades. He served the British public in prominent roles both as a young man in WWI and as an older one in WWII coordinating the Manhattan atomic bomb project. Thus, he was keenly aware of the possibilities of human extinction by the use of those weapons.
However, if we survive for a million years the human population must remain in balance with its food supply, and if we have unlimited production of babies, natural processes must determine the number of humans alive at any time. By Darwin’s Malthusian logic the population is controlled by the availability of food. In times of extreme societal stress, which in the long run must occur many times, people in the form of groups organized by some creed will fight to get the available food. Their foes will fight to protect and keep what they have and will not be spending much time and energy farming and creating food in other ways. Thus, war will not only kill many people directly but will starve many others because of the loss of land and food supply. Wars are bad for people.
Most of the time during peace, people will be living in a stratified situation based on some kind of isolation of wealth and power. The unmentioned point of this arrangement in our world of abundance is that it creates a margin of people who are happy to be just getting by in these peaceful times, living on the margins and on the streets. But when stressful times occur, short of war—that is, when there is a lack of food—it will be these people who starve to death. We have been living in an unusual situation for the last two hundred years and have come to think of food as plentiful, but in the very long run, we have a world of abundant food punctuated by famines.
The reasonable personal response to this situation is to do everything possible to avoid being in the starving margin dependent on other people’s gifts.