1. Psychic unity. All human groups were believed to possess essentially the same kind and level of intelligence and to share the same basic emotions, although individuals within groups differed from one another in these features. Because of this there was no biological barrier to the degree to which any race or nationality could benefit from new knowledge or contribute to its advancement. All groups were equally perfectable. In its most ethnocentric form this constituted a belief that all human beings were capable of benefiting from European civilization. Yet it also implied that an advanced technological civilization was not destined to remain the exclusive possession of Europeans. Cultural differences were generally either ascribed to climatic and other environmental influences or dismissed as historical accidents.
2. Cultural progress as the dominant feature of human history. Change was believed to occur continuously rather than episodically and was ascribed to natural rather than supernatural causes. The main motivation for progress was thought to be the desire of human beings to improve their condition, principally by gaining greater control over nature. Many Enlightenment philosophers regarded progress as inevitable, or even as a law of nature, while others thought of it as something to be hoped for.
3. Progress characterizes not only technological development but all aspects of human life, including social organization, politics, morality, and religious beliefs. Changes in all of these spheres of human behaviour were viewed as occurring concomitantly and as following, in a general fashion, a single line of development. As a result of similar ways of thinking, human beings at the same level of development tended to devise uniform solutions to their problems and hence their ways of life evolved along parallel lines. Cultural change was frequently conceptualized in terms of a universal series of stages. Europeans were viewed as having evolved through all of these stages, while technologically more primitive societies had passed only through the first ones.
4. Progress perfects human nature, not by changing it but by progressively eliminating ignorance, passion, and superstition. The new evolutionary view of cultural change did not negate either the traditional Christian or the Cartesian notion of a fixed and immutable human nature. Yet human nature as it was now conceived was far removed from the medieval preoccupation with sinfulness and individual dependence on divine grace as the only means of achieving salvation.
5. Progress results from the exercise of rational thought to improve the human condition. In this fashion human beings gradually acquired greater ability to control their environment, which in turn generated the wealth and leisure needed to support the creation of more complex societies and the development of a more profound and objective understanding of humanity and the universe. The exercise of reason had long been regarded as the crucial feature distinguishing human beings from animals. Most Enlightenment philosophers also viewed cultural progress technologically, as humanity's realization of the plans of a benevolent deity. A faith that benevolent laws guided human development was long to outlive a belief in God among those who studied human societies.
The Scottish philosopher Dugald Stewart labeled the
methodology that Enlightenment philosophers used to trace the development
of human institutions 'theoretic' or 'conjectural' history. This
involved the comparative study of living peoples whose cultures were judged
to be at different levels of complexity and arranging these cultures to
form a logical, usually unilinear, sequence from simple to complex. These
studies were based largely on ethnographic data derived from accounts by
explorers and missionaries working in different parts of the world. Despite
disagreement about details, such as whether agricultural or pastoral economies
had evolved first, it was believed that these sequences could be regarded
as historical ones and used to examine the development of all kinds of
social institutions. In the writings of the historian William Robertson
and others, the apparently similar sequences of cultures in the eastern
hemisphere and the Americas were interpreted as proof of the general validity
of the principle of psychic unity and of the belief that human beings at
the same stage of development would respond to the same problems in the
same way.
It is generally acknowledged that a cultural-evolutionary
perspective was widely accepted for explaining human history long before
the publication of Darwin's On the Origin of Species. Glyn Daniel
doubts the importance of Enlightenment philosophy for the development of
archaeology since Enlightenment scholars, with few exceptions, ignored
archaeological data in their own writings. That they did so is scarcely
surprising since, in the absence of any established means for dating prehistoric
materials, archaeology had little to contribute to their discussions of
cultural evolution. This does not mean, however, that the writings of the
Enlightenment did not influence the thinking of antiquarians. On the contrary,
their advocacy of an evolutionary view of human development from primitive
beginnings encouraged a more holistic understanding of prehistoric times.