A quote

From J. B. S. Haldane’s 1932 The Causes of Evolution:

… I must … discuss a fallacy which is, I think, latent in most Darwinian arguments, and which has been responsible for a good deal of poisonous nonsense which has been written on ethics in Darwin’s name, especially in Germany before the [first world] war and in America and England since. The fallacy is that natural selection will always make an organism fitter in its struggle for the environment. This is clearly true when we consider members of a rare and scattered species. It is only engaged in competing with other species, and in defending itself against inorganic nature. But as soon as a species becomes fairly dense matters are entirely different. Its members inevitably begin to compete with one another. I am not thinking only of the active and often conscious competition between higher animals, but also of the struggle for mere space which goes on between neighbouring plants of closely packed associations. … [p119]