The correct option is B Malthus's idea of population control
Darwin was impressed by Malthus's ideas. Malthus was a clergyman and economist, who wrote an essay "Principle of population as it affects future improvement of society". In this essay Malthus stated that populations can increase geometrically, while food supply can increase arithmetically only. Hence the conflict between population growth and food supply is responsible for famine, disease and war.