Theories of evolution dominated intellectual debate in Europe and America in the latter half of the nineteenth century, especially after the publication of Charles Darwin's On the Origin of Species by Means of Natural Selection (1859). Although religious authorities resisted, natural scientists and the educated public generally embraced theories of evolution. Such theories often represented human progress – or, at least, white, male, and Western human progress – as a triumph of the “survival of the fittest.”

Early Greek thinkers such as Empedocles had advanced theories of the evolution of biological species. However, most scholars during the medieval period had accepted the Aristotelian account of an immutable and hierarchical natural order, or scala naturae. Such an account not only sustained the popular conception of a purposive natural order created by a benevolent God, but also conveniently supported the notion of an immutable social hierarchy governed by kings, bishops, and the aristocracy. This account was generally accepted until the late eighteenth century and – by a good many theorists – beyond. For example, Gall's phrenology presupposed a more or less fixed hierarchy of neurological function (Young, 1990).

Nineteenth-century evolutionary theorists abandoned the notion of an immutable “great chain of being” (Lovejoy, 1936) and developed explanations of the accepted fact of species change. They generally represented evolution as a process of progressive development toward a hierarchical natural order. Jean-Baptiste Lamarck (1744–1829) and Herbert Spencer (1820–1903) advanced theories that replaced the extrinsic teleology of a divinely created natural order with the intrinsic teleology of progressive development toward a natural order. Charles Darwin (1809–1882) was the exception. His rigorously materialist theory of evolution by natural selection treated evolution as a purely mechanistic process with no extrinsic or intrinsic purpose.

Early evolutionary theories

Theories of organic evolution began to resurface in the late eighteenth century (earlier anticipations are to be found in Leibniz and Kant). The English physician Erasmus Darwin (1731–1802), the grandfather of Charles Darwin, advanced a theory of the evolution of animal traits in Zoonomia (1794–1796), later popularized in his poem The Temple of Nature (1803). His theory was an extension of Hartley's associationist psychology. Darwin generalized traditional empiricist explanations of the development of individual psychology to the evolutionary development of species by claiming that learned associations and habits engender modifications of the nervous system that are passed on to future generations of a species.