The meaning of degeneration was poorly defined, but can be described as an organism's change from a more complex to a simpler, less differentiated form, and in this respect it is associated with 19th century conceptions of biological devolution. Although rejected by Charles Darwin, the theory's application to the social sciences was supported by some evolutionary biologists, most notably Ernst Haeckel and Ray Lankester. As the 19th century wore on, the increasing emphasis on degeneration reflected an anxious pessimism about the resilience of European civilization and its possible decline and collapse.
The concept of degeneration arose during the European enlightenment and the industrial revolution - a period of profound social change and a rapidly shifting sense of personal identity. Several influences were involved.
The first related to the extreme demographic upheavals, including urbanization, in the early years of the 19th century. The disturbing experience of social change and urban crowds, largely unknown in the agrarian 18th century, was recorded in the journalism of William Cobbett, the novels of Charles Dickens and in the paintings of J M W Turner. These changes were also explored by early writers on social psychology, including Gustav Le Bon and Georg Simmel. The psychological impact of industrialisation is comprehensively described in Humphrey Jennings' masterly anthology Pandaemonium 1660 - 1886. Victorian social reformers including Edwin Chadwick, Henry Mayhew and Charles Booth voiced realistic concerns about the decline of public health in the urban life of the British working class (urban squalor). The reformers argued for improved housing and sanitation, access to parks and recreational facilities, an improved diet and a reduction in alcohol intake. These contributions from the public health perspective were discussed by the Scottish physician Sir James Cantlie in his 1885 lectures Degeneration Amongst Londoners. The novel experience of everyday contact with the urban working classes gave rise to a kind of horrified fascination with their perceived reproductive energies which appeared to threaten middle-class culture.
Secondly, the proto-evolutionary biology and transformatist speculations of Jean-Baptiste Lamarck and other natural historians—taken together with the Baron von Cuvier's theory of extinctions—played an important part in establishing a sense of the unsettled aspects of the natural world. The polygenic theories of multiple racial origins, supported by Robert Knox in his book The Races of Men (1850), were firmly rejected by Charles Darwin who, following James Cowles Prichard, generally agreed a single African origin for the entire human species.