Social Darwinism

"Man, like every other animal, has no doubt advanced to his present high condition through a struggle for existence consequent on his rapid multiplication; and if he is to advance still higher, it is to be feared that he must remain subject to a severe struggle." Darwin

Darwin's insight that, as long as population was regulated by Malthusian mechanisms, mankind would be subject to natural selection was profoundly correct.

Preindustrial England in the  years 1250-1800
Economic success translated powerfully into reproductive success, with the richest individuals having more than twice the number of surviving children at death as the poorest.

Clark (2007) A Farewell to Alms Ch.6 p.112