"Darwin got his idea fro natural selection for the economics of the invisible hand. It convinced him that just as unplanned economies produce the best results, natural selection produces the most robust biological designs."
It appears that he actually got his idea from reading Malthus:
"The art of plant and animal breeding had existed for a long time. The step Darwin took was to postulate a similar process in nature. Presupposing that spontaneous variation somehow occurs, he postulated a process of selection, not by a human plant or animal breeder, but by nature. What could this process be? The answer occurred to him when he was reading Malthus on population. Wallace also got the idea from Malthus. (See Leakey (ed.), The Illustrated Origin of Species, pp. 9 and 10.) What Malthus said of the human population--that every pair produces more than two offspring and that there is a tendency to outstrip the food supply--occurs with every species. Just as the human population is checked and reduced from time to time by starvation, disease, war etc., so the population of every plant and animal species is checked from time to time by lack of food, predation, etc. Whatever the checks, only some individuals will survive and propagate; what matters in this context is not the parents' survival but propagation and the survival to the breeding stage of their offspring. Nature thus selects for breeding those individuals whose characteristics fit them best to survive and propagate in the face of whatever it is that is checking and reducing this population. If the check is a harsh climate, then nature selects those best fitted to survive and reproduce in a harsh climate. Notice that there is selection without any selector."
From here: http://www.humanities.mq.edu.au/Ockham/y64l051.html
Now, if I recall correctly, Malthus is a darling prophet to the environmental whacko leftists. Libertarian economists have neatly linked Darwinism to the Invisible Hand stuff, but it appears Darwin himself did not.
- Auguste Comte’s Cours de Philosophie Positive
- various works of the Belgian statistician Adolphe Quetelet
- Dugald Stewart’s On the Life and Writing of Adam Smith