Theories of population

Population theory asks why populations grow, stabilise or shrink. Malthus argued population grows geometrically (doubling each generation) while food grows arithmetically, so positive checks (famine, disease) and preventive checks (delayed marriage, restraint) hold numbers back — a gloomy view in which rising living standards are eaten by more mouths. Demographic transition theory is more optimistic and better fits history: societies move from high birth and death rates, through a phase where deaths fall first (so population surges), to low birth and death rates with slow or no growth. Worked example: a population of 100 million growing at 2% a year doubles in about 70/2 = 35 years (the rule of 70).