Reviewing Darrin M. McMahon’s Divine Fury: A History of Genius, Tamsin Shaw relays his understanding of why the term “genius,” in its modern sense, arose in the 18th century:
McMahon’s account is not, as we might expect, rooted in the inexplicability of certain human achievements, the perceived inability to comprehend them in purely natural terms. Rather, he suggests that two fundamental transformations in human thought created the need for such a conception. The first was the process of disenchantment through which God came to seem increasingly remote from human life as belief in his intermediaries among us—spirits, angels, prophets, apostles, and saints—was eroded. McMahon hypothesizes that this created a sense of abandonment, a need for “assurance that special beings still animated the universe.”
The second relevant transformation, he tells us, was the emergent belief, from the seventeenth century on, in the natural equality of all human beings, a belief that provoked as a powerful reaction an insistence that we recognize naturally superior beings. The cult of the genius arose as a response to this dual challenge, identifying a species of being “who walked where the angels and god-men once trod.”
The Dish 