David Attenborough asks a blunt question: is there a limit to how many humans the planet can support, and are we already past it? He traces world population from one billion in 1800 to nearly seven billion today, and visits the places where growth and consumption collide, from crowded housing blocks to the fields and fisheries feeding them. Demographers and ecologists lay out competing forecasts for where the numbers plateau, while economists argue that rising consumption in wealthy countries, not sheer headcount, does the real damage to resources. The film looks at China's one-child policy as one blunt attempt at control, and at falling birth rates in parts of Europe as evidence that education and prosperity can slow growth without coercion. Attenborough weighs food supply, water, and energy against projected population curves, and lets scientists on different sides of the debate make their case directly to camera. It ends without a fixed number, only a clearer sense of what has to change if there is one.