The idea --- not invented, but highlighted and made more prominent by Darwin and his successors --- that the human race itself is a product of a process of competition resulting in selection on the one hand, and salutary extinctions on the other, gave fresh inspiration to social Darwinists like Herbert Spencer and Darwin's cousin Sir Francis Galton. Darwin's writings are also prominently cited by racial superiority advocates and eugenicists like Sydney and Beatrice Webb, Bertrand Russell, Oliver Wendell Holmes and Adolf Hitler.
Although he is not responsible for exaggerations and misapplications by his soi-disant disciples, Right and Left, Darwin had persuasive ideas about racial progress; and ideas have consequences.
Around 400 BC Plato, writing in The Republic, suggested "The best men must have intercourse with the best women as frequently as possible, and the opposite is true of the very inferior." Humans, being as they say closer to the earth those days, easily saw the similarities between man and animal. Breeding humans was as logical as breeding animals. We even have their imagery of half-human half-animal breeds (such as the Centaurs, etc.)
Darwin's insight was not that even humans could be breed. He simply illustrated the natural selective mechanism that propelled evolution.
To credit or blame him for attempts at human breeding is at least several thousand years too late.
Modern eugenics incorporated the more scientifically grounded basis of Darwin, but they would have existed regardless. Just as they have incorporated modern genetics.