Charles Darwin, famed for his development of the theory of evolution based on natural selection and descent with modification, has been cited countless times since the publication of On the Origin of Species in the mid-1800s and is probably the most famous biologist in history.

But Darwin himself cited, among other sources, the essay on population and overall work on the power of population dynamics of another British intellectual, Thomas Robert Malthus, when explaining what inspired and shaped his theory. Malthus believed that the world's food supply was and could be never be sufficient to keep pace with the rate of population growth in his day.

He criticized the laws of the land and the overall political economy for promoting larger communities of poor people without genuinely providing for a quality of life among the needy.

This is similar to endless arguments about the "welfare state" in Western civilization today, and advocated for both a higher level of "moral restraint" (i.e., abstinence) and synthetic birth control, especially among the lower classes, to help achieve this aim.

Thomas Malthus was born in 1766. By the standards of his or any era, he was a highly educated academic. By trade, he was an economist and population scientist as well as a cleric.

In 1798, Malthus anonymously published his now-famous paper An Essay on the Principle of Population.

While not a trained biologist, Malthus had observed that plants, animals and people often "overproduce" offspring via an inflated birth rate – that is, their numbers exceed the level of sustenance available in their environment that is adequate to support the population.

He predicted that there would arise an inability of resources (particularly food) to keep up with increasing population growth worldwide.

Malthus viewed poverty, hunger and lack of sufficient food production to feed all of the world's people as an inevitable part of the human experience. In accordance with the less secular standards of the science-minded during his lifetime, he believed this arrangement was put in place by God to keep people from being lazy.

His ideas went against the prevailing wisdom at the time, which was that with enough laws and the proper social structures, human ingenuity could overcome any level of sickness, hunger, poverty and so on.

Malthus, in fact, failed to foresee the technological advances that have allowed humanity to keep pace with exponential population growth (at least so far). As a result, at least as of the second decade of the 21st century, Malthus' predictions have not been borne out in reality.

Before Malthus and Darwin, the scientific consensus was that organisms produced just enough food to maintain their population, meaning that production and consumption were closely and efficiently matched.

Darwin, who was also from England but did much of his field work outside Great Britain, connected Malthus' ideas to how things survive in the wild, concluding that organisms overproduce by default because many of them are eliminated before reaching reproductive age owing to factors such as predation and lethal illnesses.

Darwin saw that certain individuals in this scheme of overproduction were better suited to survive than to others.

He attributed this realization to Malthus' description of the inherent struggle for existence, and Darwin connected this to his notion of "survival of the fittest." This idea is widely misunderstood and refers not to individuals willfully becoming fitter, but to those who happen to have inherited traits that make them more likely to survive and reproduce in a given environment.

With no small degree of smugness, modern scholars have suggested that Malthus' doomsday predictions were predicated on flimsy ideas and a flawed and cynical understanding of the ingenuity of future generations of human beings, as occurred in the Industrial Revolution in Europe (especially Britain) and the United States after his death in the 1800s.

Still, if the world's population continues to grow at its present rate, factors other than increased food production may be necessary to sustain population growth beyond 9 or 10 billion people, about 2 to 3 billion in excess of the world total as of 2019.

Many scientists believe that even if the food supply can be maintained at adequate levels per se, the environmental consequences will be such that sustainability measures will fail for secondary reasons (e.g., climate change, pollution, etc.). In some ways, these arguments appear to parallel Malthus' own in that they may fail to account for technological leaps capable of surmounting such challenges.