“After my return to England [2 Oct 1838] it appeared to me that by following the example of Lyell in Geology, and by collecting all facts which bore in any way on the variation of animals and plants under domestication and nature, some light might perhaps be thrown on the whole subject.... I worked on true Baconian principles, and without any theory collected facts on a wholesale scale, more especially with respect to domesticated productions, by printed enquiries, by conversation with skillful breeders and gardeners, and by extensive reading.... I soon perceived that selection was the keystone of man's success in making useful races of animals and plants. But how selection could be applied to organisms living in a state of nature remained for some time a mystery to me. In Oct 1838, that is, fifteen months after I had begun my systematic enquiry, I happened to read for amusement Malthus on Population, and being well prepared to appreciate the struggle for existence which everywhere goes on ... it at once struck me that under these circumstances favorable variations would tend to be preserved, and unfavorable ones to be destroyed. The result of this would be the formation of new species. Here, then, I had at last got a theory by which to work.”

— Charles Darwin (1887), Autobiography (Ѻ)

“One may say there is a force like a hundred thousand wedges trying [to] force every kind of adapted structure into the gaps in the oeconomy of nature, or rather forming gaps by thrusting out weaker ones ... The final cause of all this wedging, must be to sort out proper structure and adapt it to change.”

— Charles Darwin (1838), Transmutation Notebook D (made directly after some comments on Malthus) (Ѻ), Sep 28

“Malthus claimed that the human population expanded geometrically [1, 2, 4, 8, 16, 32, …], doubling every 25 years on average, while agricultural production increased only arithmetically [1, 2, 3, …]. Therefore, the population must ineluctably be controlled in the struggle for sustenance and reproduction by such checks as famine, epidemics, wars, abortion, infanticide, contraception, or at best moral self-restraint in the form of late marriage and sexual abstinence. Society, said Malthus, must recognize this underlying statistical cause of misery and vice, and look for logical ways to alleviate them.”

— Andrew Robinson (2020), Sudden Genius [2]

A general diagram of the Malthus model, according to which food production increases linearly, whereas population increases geometrically, and that overtime the "power" of population will be checked by the "law of necessity".

“It is an acknowledged truth in philosophy that a just theory will always be confirmed by experiment.”

— Thomas Malthus (1798), An Essay on the Principle of Population (§1) (Ѻ)

“Taking the whole earth instead of this island, emigration would of course be excluded; and supposing the present population equal to a thousand millions, the human species would increase as the numbers 1, 2, 4, 8, 16, 32, 64, 128, 256, and subsistence as 1, 2, 3, 4, 5, 6, 7, 8, 9. In two centuries the population would be to the means of subsistence as 256 to 9; in three centuries as 4096 to 13, and in two thousand years the difference would be almost incalculable. In this supposition no limits whatever are placed to the produce of the earth. It may increase for ever, and be greater than any assignable quantity; yet still the power of population being in every period so much superior, the increase of the human species can only be kept down to the level of the means of subsistence by the constant operation of the strong law of necessity acting as a check upon the greater power.”

— Thomas Malthus (1798), An Essay on the Principle of Population (pg. 8)

“The poverty and misery arising from too rapid increase of population, had been distinctly seen, and the most violent remedies proposed, so long ago as the times of Plato and Aristotle.”

— Thomas Malthus (1803), “Preface” to revised edition of An Essay on the Principle of Population (iv)