Malthusian narrative is a population + resource theory proposed by the Reverend Thomas Robert Malthus. In sum, when unchecked or uncontrolled, population will grow exponentially, while our resources, like food, will not grow as fast. Thus, unchecked population growth will be met with famine and other sufferings. You might have guessed, this idea later developed into the whole idea of advocating for population control. Overall, not a happy thought.

Whether it is empirically supported or not, it holds a great power over how people think about sustainability.