Frances Austin (1985) points out in her paper named Relative Which in Late 18th Century Usage: The Clift Family Correspondence that the relative pronoun which in the eighteenth century was not predominantly used for inanimate objects (pp.15-29). Instead this relative pronoun was sometimes implemented in sentences “with a personal or human antecedent. The three oldest writers, Elizabeth, John and Thomas all occasionally use which with a personal antecedent” (1985, p. 17). At least three of the six siblings in the Clift family combined in their letters the relative pronoun which with a human antecedent. However, the usage of the relative pronoun who in combination with a personal antecedent has been a widespread practice since the seventeenth century. Nonetheless, some famous grammarians also still used the relative pronoun which with human antecedents. For instance, Noah Webster used the relative pronouns which with both human and inanimate antecedents in his texts from 1807 (1985, p. 18). Even though eighteenth century grammarians restricted the grammatical usage of the relative pronoun which to only inanimate objects, analyses of eighteenth century letters prove that this was not always the case.
Austen, Frances. (1985). “Relative Which in Late 18th CenturyUsage: The Clift Family Correspondence” In: Roger Eaton et al. (eds). Papers from the 4th International Conference on English Historical Linguistics. Amsterdam: John Benjamins Publishing Company.