These works told the story, in different ways, of man’s fall from ancient wisdom into modern atheism and scepticism……. In both works Monboddo set out to trace the orgins of civil society, and show the superiority of much of antiquity to much of modernity (including politically!). The orangutans had a particularly important role in Monboddo’s arguments, for in arguing that orangutans were human, and that humanity was independant of the use of language, he presented the state of nature as very much extant. Although Monboddo thought orangutans not to be animals, his arguments went a long way towards blurring the line between humans and the higher primates, and showing that the higher primates could be considered our equals both morally and socially (even if lacking in language).
A.V. Garrett, Animal Rights and Souls in the Eighteenth Century