Part of the difficulty in establishing sensible and consistent usage is that commitment to the biology of natural selection and to ‘survival of the fittest’ entailed nothing uniform either for sociological method or for political doctrine. A ‘social Darwinist’ could just as well be a defender of laissez-faire as a defender of state socialism, just as much an imperialist as a domestic eugenicist (McLean, 2009, p. 490).

Nevertheless, the term has a certain cache, and longstanding usage to describe tenets that were developed by, or spun-off from, Darwin’s (1859) original thesis that applied to biological concepts of natural selection and survival; and were then extended to the “survival of the fittest” in sociology and politics. Darwin’s concept of evolutionary adaptation through natural selection became central to modern evolutionary theory, and it has now become the unifying concept of the life sciences.

Darwin’s theory of evolution is based on key facts and the inferences drawn from them, which biologist Mayr (1982), summarized as follows:

Every species is fertile enough that if all offspring survived to reproduce the population would grow (fact).

  • Despite periodic fluctuations, populations remain roughly the same size (fact).
  • Resources such as food are limited and are relatively stable over time (fact).
  • A struggle for survival ensues (inference).
  • Individuals in a population vary significantly from one another (fact).
  • Much of this variation is heritable (fact).
  • Individuals less suited to the environment are less likely to survive and less likely to reproduce; individuals more suited to the environment are more likely to survive and more likely to reproduce and leave their heritable traits to future generations, which produces the process of natural selection (fact).
  • This slowly effected process results in populations changing to adapt to their environments, and ultimately, these variations accumulate over time to form new species (inference) (pp. 479-480).