As Edward Hall explains in The Hidden Dimension, all animals react the same way in response to stress caused by overcrowding and scarcity. The first-stage reaction is to test the boundaries of the community, to see whether it can expand and take over more land to relieve the pressure. If that is unsuccessful, the second-stage reaction is a form of shock, fueled by an overload of secreted adrenaline that produces hyperactivity, depression, distraction, and metabolic instability, which lead in turn to higher rates of spontaneous abortion, lower fertility, and more suicides. If even this is insufficient to reduce numbers and alleviate overcrowding and scarcity, the third-stage reaction is a form of madness: war, violent and unprovoked aggression, mass suicide, and the eating of the young. This ‘last resort’ ensures that no species can seriously disrupt the ecological balance of life long enough or severely enough to produce an ecological crash. It’s the self-regulating process that has worked well since the first living creatures appeared on the planet three billion years ago.
Is the human species entering this third-stage state of reaction?