Final answer:
Thomas Malthus posited that without preventative checks on population growth, overpopulation would be corrected by catastrophic events like famine, war, and disease. His theory emphasized that these 'positive checks' would control populations exceeding the earth's carrying capacity.
Step-by-step explanation:
The theorist who suggested that without preventative checks on population growth such as birth control and celibacy, overpopulation would lead to catastrophic checks like famine, war, and disease was Thomas Malthus. In his work An Essay on the Principle of Population, published in 1798, Malthus argued that while population tends to grow exponentially, food supply increases only arithmetically. This disparity would inevitably lead to overpopulation, which would then result in catastrophic 'positive checks'—Malthus's term for events that increase mortality and thus keep population numbers under control.
Malthus identified war, famine, and disease as positive checks. He observed that as the population grows, resources would become scarce, causing strife among societies that would resort to war, while others would face famine and disease due to the inability to sustain the growing numbers. These crises would cyclically reduce the population until it became manageable again. Malthus's theory has been influential, notably impacting Charles Darwin's theory of natural selection, though later developments in agricultural productivity and family planning methods have provided counterpoints to some of Malthus's more dire predictions.
Thomas Malthus suggested that without preventative checks, overpopulation would lead to catastrophic checks such as famine, war, and disease, to keep population growth in check.