Problem

Suppose that in the year 2100, the world population has stabilized at 10 billion people. A hypothetical country Zed has a population of 50 million and its agricultural lands are gradually deteriorating. Prior to this, Zed had had a prolonged period of improvement in living conditions, but in the last decade, these living improvements were followed by a sharp period of decline due to the rapidly growing population, decreasing food resources, the lagging behind of the public infrastructure. According to the “J-curve hypothesis”, under such circumstances, citizens face these injustices and would rise up in the social system to engage in collective rebellion. The J-curve is presented below in Figure 1.
Figure 1: J-curve, demonstrating the gap between expectations and reality
The basic argument is that persistent growth and improvement leads people to develop psychological expectations that things will continue to get better. When such expectations are suddenly thwarted, people experience an intolerable gap between expectations and realities of their circumstances. Essentially, this explains how individuals decide to riot or rebel based on a set of “psychological ideas”--if there is a gap between their psychological expectations and environmental reality, and this frustration is not addressed, they will respond with aggression.
What is a possible explanation as to why the world population stabilized at 10 billion people?
Please choose from one of the following options.
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