Herbert Spencer 

He (27 April 1820 – 8 December 1903) was an English philosopher, biologist, anthropologist, sociologist, and prominent classical liberal political theorist of the Victorian era.

Spencer developed an all-embracing conception of evolution as the progressive development of the physical world, biological organisms, the human mind, and human culture and societies. As a polymath, he contributed to a wide range of subjects, including ethics, religion, anthropology, economics, political theory, philosophy, literature, astronomy, biology, sociology, and psychology. 

Spencer read with excitement the original positivist sociology of Auguste Comte. A philosopher of science, Comte had proposed a theory of sociocultural evolution that society progresses by a general law of three stages. Writing after various developments in biology, however, Spencer rejected what he regarded as the ideological aspects of Comte's positivism, attempting to reformulate social science in terms of his principle of evolution, which he applied to the biological, psychological and sociological aspects of the universe.

Given the primacy which Spencer placed on evolution, his sociology might be described as social Darwinism mixed with Lamarckism. However, despite its popularity, this view of Spencer's sociology is mistaken. While his political and ethical writings had themes consistent with social Darwinism, such themes are absent in Spencer's sociological works, which focus on how processes of societal growth and differentiation lead to changing degrees of complexity in social organization 

The evolutionary progression from simple, undifferentiated homogeneity to complex, differentiated heterogeneity was exemplified, Spencer argued, by the development of society. He developed a theory of two types of society, the militant and the industrial, which corresponded to this evolutionary progression. Militant society, structured around relationships of hierarchy and obedience, was simple and undifferentiated; industrial society, based on voluntary, contractually assumed social obligations, was complex and differentiated. Society, which Spencer conceptualised as a 'social organism' evolved from the simpler state to the more complex according to the universal law of evolution. Moreover, industrial society was the direct descendant of the ideal society developed in Social Statics, although Spencer now equivocated over whether the evolution of society would result in anarchism (as he had first believed) or whether it pointed to a continued role for the state, albeit one reduced to the minimal functions of the enforcement of contracts and external defense.

Survival of the fittest

"Survival of the fittest" is a phrase that originated from Darwinian evolutionary theory as a way of describing the mechanism of natural selection. The biological concept of fitness is defined as reproductive success. In Darwinian terms the phrase is best understood as "Survival of the form that will leave the most copies of itself in successive generations."

Herbert Spencer first used the phrase, after reading Charles Darwin's On the Origin of Species, in his Principles of Biology (1864), in which he drew parallels between his own economic theories and Darwin's biological ones: "This survival of the fittest, which I have here sought to express in mechanical terms, is that which Mr. Darwin has called 'natural selection', or the preservation of favoured races in the struggle for life.

Herbert Spencer (1820–1903) was an English philosopher who initiated a philosophy called ‘Social Darwinism’. He coined the term ‘survival of the fittest’ seven years before Darwin’s publication of his theory of natural history, The Origin of the Species in 1859. Spencer became an enthusiastic supporter of Darwin’s theory of evolution, believing it could also be applied equally well to human societies.

Evolution and Natural Selection

According to Darwin’s theory of evolution, only the plants and animals best adapted to their environment will survive to reproduce and transfer their genes to the next generation. Animals and plants that are poorly adapted to their environment will not survive to reproduce. Darwin’s theory of evolution by natural selection was a scientific theory focused on explaining his observations about biological diversity and why different species of plants and animals look different.

Survival of the Fittest and Laissez-Faire Capitalism

After Darwin published his theories on biological evolution and natural selection, Herbert Spencer drew further parallels between his economic theories and Darwin’s scientific principles. Spencer applied the idea of “survival of the fittest” to so-called laissez faire or unrestrained capitalism during the Industrial Revolution, in which businesses are allowed to operate with little regulation from the government. Unlike Darwin, Spencer believed that people could genetically pass learned qualities, such as frugality and morality, on to their children. Spencer opposed any laws that helped workers, the poor, and those he deemed genetically weak. Such laws, he argued, would go against the evolution of civilization by delaying the extinction of the “unfit.” Another prominent Social Darwinist was American economist William Graham Sumner. He was an early opponent of the welfare state. He viewed individual competition for property and social status as a tool for eliminating the weak and immoral of the population.

Nazi Germany

Adolf Hitler, one of the world’s most notorious eugenicists, drew inspiration from California’s forced sterilizations of the “feeble-minded” in designing Nazi Germany’s racially based policies. Hitler began reading about eugenics and social Darwinism while he was imprisoned following a failed 1924 coup attempt known as the Beer Hall Putsch. Hitler adopted the social Darwinist take on survival of the fittest. He believed the German master race had grown weak due to the influence of non-Aryans in Germany. To Hitler, survival of the German “Aryan” race depended on its ability to maintain the purity of its gene pool. The Nazis targeted certain groups or races that they considered biologically inferior for extermination. These included Jews, Roma (gypsies), Poles, Soviets, people with disabilities and homosexuals. By the end of World War II, social Darwinist and eugenic theories had fallen out of favor in the United States and much of Europe—partly due to their associations with Nazi programs and propaganda, and because these theories were scientifically unfounded.