This belief coupled with the idea of a struggle for existence among species and races and the popularization of the slogan "survival of the fittest" provided the rationale and justification for much of the horrific treatment of blacks in the Americas and as much or more in Africa.
It's estimated, for example, that between the years 1885 to 1908 the Belgians under Leopold II were responsible for the deaths of ten million Congolese. These indigenous people were systematically tortured and slaughtered as though their existence meant nothing.
Men, women and children had their hands amputated when the quota of rubber was not met. Others were shot for sport. Countless more starved to death in slave labor or died from diseases.
Robert Conrad's novella Heart of Darkness (1899) conveys something of the vicious attitude of the Europeans toward the indigenous people of the Congo and the horrific treatment to which they were subjected. Conrad has the main character of the story, Charlie Marlowe, accidentally come upon a group of sick and dying Africans who had been impressed by the Europeans into labor gangs, languishing in a grove of trees:
Black shapes crouched, lay, sat between the trees leaning against the trunks, clinging to the earth, half coming out, half effaced within the dim light, in all the attitudes of pain, abandonment, and despair....[Meanwhile] the work was going on. The work! And this was the place where some of the helpers had withdrawn to die.David McCullough's account of the early efforts by the French to build the Panama Canal with black labor brought in from the West Indies in his book Between the Seas tells a similar tale of the late 19th century attitude of the Europeans toward blacks.
They were dying slowly - it was very clear....they were nothing earthly now - nothing but black shadows of disease and starvation, lying confusedly in the greenish gloom....Brought from all the recesses of the coast ...lost in uncongenial surroundings, fed on unfamiliar food, they sickened, became inefficient, and were then allowed to crawl away and rest.
These moribund shapes were as free as air - and nearly as thin.
My point is not to indict whites as uniquely evil, as the Critical Race Theorists would have it. I'm quite sure that, even though it couldn't be proven, if the circumstances were reversed and blacks had the same power over others in the 19th century as did whites, they would've been every bit as cruel as were the Europeans.
Cruelty is an inherent trait of the human condition. It's not, contra the Critical Race Theorists, the exclusive vice of any particular race.
My point is rather to observe that the attitude among Europeans of racial superiority and their belief that black Africans were less valuable even than their livestock, and certainly more expendable, was a direct consequence of the widespread acceptance in the late 1800s of Darwinian evolution.
On naturalistic Darwinism there's really no reason why anyone who is inclined to treat others as inferiors, to treat them cruelly, and who has the power to do so, shouldn't. Naturalistic Darwinism offers no basis for a moral objection to racism. It renders moral sentiments no more authoritative than any other vestige of our evolutionary history.
Moreover, according to the accepted Darwinian intellectual climate shaped by Darwinism, some races really were superior and others really were inferior, and Darwin himself wrote in The Descent of Man (1871) that the savage races would one day be extirpated by the superior races in the struggle for survival. Europeans simply saw themselves as carrying out nature's imperative.
Anyone who doubts that Darwinian assumptions in the 19th and early 20th century led to utterly cruel and inhumane treatment of Africans and other peoples from around the world would do well to watch this 50 minute documentary on the subject: There's nothing in Darwinian naturalism that makes racism and cruelty wrong. The only basis that exists for condemning these evils is the belief that everyone is equal in the eyes of God in whose image we all share and who holds all of us accountable for how we treat each other. Take that belief away and we're back to an amoral dystopia like the Belgian Congo or Panama in which might makes right - the strong flourish and the weak perish.