From Darwin: Portrait of a Genius, on how the dominant ideas of the 20th century were used to both good and bad ends (Freudian psychology was used to sell cigarettes, Marx’s labor theories sentences millions to lives of fruitless toil, and Einstein’s physics were used to create the most power bomb imaginable):
The truth is, Origin is a book that, with total success, embodies an exciting idea and had a devastating intellectual and emotional impact on world society. The word devastating is accurate: It destroyed many comfortable assumptions, thus clearing space for new concepts and ideas to spring up in almost every subject. It acted like a force of nature itself, and by the end of January 1860, when the second edition sold out, it was quite beyond Darwin’s control. Darwin became one of the formative thinkers of the twentieth century, alongside Marx, Freud, and Einstein, affecting the way people thought about an immense variety of topics, often quite remote from his own preoccupations.
However, not all was for good. We see, for instance, how Hitler perverted Darwin’s theories:
What made his teaching so destructive in Germany was his emphasis on the constant violence involved in natural selection. It is doubtful if Adolf Hitler actually read the Origin, but he certainly absorbed its arguments and the psychology of strife seen as necessary for the emergence of higher forms. Hitler was fond of dwelling on the awful prospect (which Thomas Carlyle had made into a joke) of mankind evolving backward or downward. He said:
“If we do not respect the law of nature, imposing our will by the might of the stronger, a day will come when the wild animals will again devour us—when the insects will eat the wild animals, and finally nothing will exist except the microbes. By means of the struggle the elites are continually renewed. The law of selection justifies this incessant struggle by allowing the survival of the fittest. Christianity is a rebellion against natural law, a protest against nature.”
Thus we see how ideas develop their own self-sustaining and often destructive careers in history. The emotional stew that built up inside Darwin’s mind from seeing the Fuegans, looking at beaks in the Galapagos, and reading Malthus—a stew that permeated with is verbal odors almost every page of Origin—becam for some a vicious poison. Darwin’s fondness for the word struggle—he used it dozens of times—was particularly unfortunate. Hitler adopted it and made it the title of his book, which was both autobiography and political program, Mein Kampf. Struggle was healthy; it was nature’s way. And under the cover and darkness of war, it became easy to resort to another much-used word of Darwin’s, extermination.