In her chapter, Silvia Sebastiani treats Scottish Enlightenment thinking about the history of society as the product of a dialogue with natural history as well as moral philosophy. The key reference points were Buffon’s Natural History and Rousseau’s Discourse on inequality: from these the Scots derived two rival accounts of how natural man became historical. One conceived of history as the ‘progress of society’ through successive ‘stages’ of development, culminating in the attainment of ‘civilisation’. With contributions from David Hume, Adam Ferguson and Adam Smith, this account was premised on the idea of a uniform human nature, but did not exclude the possibility of hierarchies between humans, and attached lesser value to forms of social organisation preceding civilisation. The alternative, explored at length by Lord Monboddo, a practising judge, took Rousseau’s assertion of the ‘perfectibility’ of man as an invitation to appreciate the variety of ways (physical as well as moral) in which humans might develop, and to accept that quite different outcomes were possible, corruption and decline as much as progress. There was no single Scottish conception of the ‘progress of society’, and the normative implications of stadial history were less uniformly positive than its later admirers have supposed.

The normalization of the elect acquired a corresponding theoretical framework. From the late seventeenth century the preferred explanation for physical growth had been ‘preformation’: the theory, starting with Swammerdam, that all living organisms have pre-existed from the Creation and are born as miniature versions which ‘unfold’ through predetermined stages. Leibniz suggested applying preformationism to the human mind. It was in this context that the word itself, ‘development’ (whose first appearances are better translated as ‘unfolding’), was first employed. The pioneering naturalist Charles Bonnet went on to apply the theory of preformationism to what he now expressly termed ‘psychology’. He identified psychology with the stages of regeneration in the elect (the so-called economy of grace); he linked this development of the person to the Enlightenment idea of ‘social progress’, and represented both as a gradual (rather than instantaneous) unfolding of biblical Revelation.

This essay examines the degeneration thesis, as formulated by Buffon and taken up in the so-called dispute of the New World. Early colonial observers such as Acosta and Catesby engaged with the classical climate-determinist paradigm, with its north–south orientation of climate zones. Buffon drew on these natural history observations, Enlightenment social theory, and the new geoscience and reoriented climate determinism on an east–west axis. Buffon posited that America had emerged more recently than Europe from oceanic submergence and was thus colder and wetter – and that therefore America’s climate was more favorable to the production of supposedly inferior animals such as insects and reptiles and less favorable to larger mammals and humans. Implications for human development were vigorously contested by Americans such as Jefferson and reoriented again along a global north–south axis, notably by Hegel. The degeneration thesis enjoyed a long legacy, surfacing in the United States in nativist-populist responses to demographic issues. The essay concludes by identifying two such episodes, early twentieth-century nativism and the new nativism of the twenty-first century.