Malthus argued, in contrast, that it was a law of nature that society could never improve because when times were good, population would rise only to be checked by famine, war and disease. As he wrote in his famous book, An Essay on the Principle of Population,
Assuming then my postulate as granted, I say, that the power of population is indefinitely greater than the power in the earth to produce subsistence for man.
Population, when unchecked, increases in a geometrical ratio. Subsistence increases only in an arithmetical ratio. A slight acquaintance with numbers will shew the immensity of the first power in comparison of the second.
By that law of our nature which makes food necessary to the life of man, the effects of these two unequal powers must be kept equal.
This implies a strong and constantly operating check on population from the difficulty of subsistence. This difficulty must fall somewhere and must necessarily be severely felt by a large portion of mankind.
In reading Mr Godwin's ingenious and able work on Political Justice, it is impossible not to be struck with the spirit and energy of his style, the force and precision of some of his reasonings, the ardent tone of his thoughts, and particularly with that impressive earnestness of manner which gives an air of truth to the whole. At the same time, it must be confessed that he has not proceeded in his inquiries with the caution that sound philosophy seems to require. His conclusions are often unwarranted by his premises. He fails sometimes in removing the objections which he himself brings forward. He relies too much on general and abstract propositions which will not admit of application. And his conjectures certainly far outstrip the modesty of nature.Godwin rose to the bait, much against his better judgement, and wrote a rebuttal to Malthus's treatise. He didn't buy the idea that population rose geometrically, and he demanded proof.
And Godwin was right. Indeed, as discussed by the experts on In Our Time, Malthus basically made up the idea of geometrically increasing population vs arithmetically increasing food supplies out of whole cloth. The idea was that population doubles every generation because the number of offspring next generation is proportional to the number of parents in this generation: each parent more than reproduces him/herself. But agricultural progress on fixed amounts of acreage only increase gradually--even if by some amount per year, it's not as fast as population growth (Malthus said). But the argument was bolstered by little more than vague data and lots of hand-waving.
Yet from then, through his inspiration of Darwin and Wallace as a justification of natural selection, it is still believed. Even in Malthus' time, population was not in excess of resources.
This shows how close examination can reveal things that casual acceptance misses: we ourselves, as evolutionary biologists, have read, re-read, and marked-up Malthus, and read Darwin's and Wallace's comments about Malthus, yet were so blinded that we did not question the evidence for the differential growth assertions.
Overpopulation is a reality, but many specialists debate what, when, where, and how that is the case, and not everyone today accepts Malthus' basic tenets. Indeed, pro-business interests say that industry can feed everyone and it's just politics that prevents the distribution.
Darwin and others extended--at their own recognizance and not really taking from Malthus--the idea that the struggle was not just the population against the environment, but among the population because of the environmental constraint. Again, this is a whole-cloth extension, basically. Indeed, Wallace was more about populations (species) against environment than about mano a mano competition.
Only if it was a true Law of Nature, and not something that just happened now and then, would overpopulation force natural selection. It is manifestly and obviously true that in almost all circumstances the vast, vast majority of indivduals are not on the very edge of survival, scrawny, scrambling for the last scrap so they can screw one more time and perpetuate their genotypes. There are competitive elements in Nature, to be sure, but they are much less law-like and ubiquitous, and there are other ways than just selection for evolution to occur.
The canonization of Malthus, who was largely defending the privileged monarchy against Utopian idealists, shows how an idea, easy, simplistic and appealing even if badly flawed even at the time, can come to dominate and drive even an important area of scientific theory inhabited by people as intelligent and well-trained as there are. It isn't the first time in the history of science that poorly supported theory has survived (Galen, phlebotomy, celestial spheres, Genesis). It's more the rule than the exception. So why then are we so convinced by this one?
This does not imply that population can't or doesn't often press up against carrying capacity, nor that this cannot sometimes induce competition. But it does imply that such is not a fundamental law of life, and it forces us--if we recognize the truth of it--to think more subtly about the many forms of differential reproduction that as far as we know must be possible for the diversity and adapted nature of life.
And it should force us to be a little more humble about our own wise insights and theories.....