Why did social Darwinism decline during the twentieth century?

Social Darwinism, a theory popularized by the British philosopher Herbert Spencer, declined during the 20th century as expanded knowledge in biological, social, and cultural fields undermined its core tenets.1

The theory, which applied the concept of natural selection and "survival of the fittest" to human societies, was used to justify laissez-faire capitalism, class stratification, and racist or imperialist policies. Its decline was driven by several factors:1

• Scientific Advancement: As scientific understanding of genetics and human behavior evolved, the simplistic biological analogies used by social Darwinists were increasingly viewed as scientifically invalid.12
• Ethical Rejection: The association of these ideas with eugenics and the atrocities committed by the Nazis—who used such theories to rationalize the extermination of entire groups—led to widespread moral condemnation.32
• Academic Critique: Social scientists and philosophers criticized the theory for its lack of empirical support and its tendency to serve as a mere justification for the social status quo.45

Ultimately, the intellectual and moral failure of these assumptions caused the theory to lose its standing as a credible framework for understanding human society.12