Primate taxonomists have identified six living species of non-human great apes: Sumatran and Bornean orangutans, eastern and western gorillas, chimpanzees, and bonobos. The Sumatran and Bornean orangutans were first identified as separate species in 2001. Now, a team of biologists has identified a third orangutan species--the Tapanuli orangutan Pongo tapanuliensis (pictured above). The orangutans are our most distant evolutionary relatives among the living hominids, and now the Tapanuli orangutan seems to be the oldest evolutionary lineage in the genus Pongo. The New York Times has an article on this, which includes a link to the report: Alexander Nater et al., "Morphormetric, Behavioral, and Genomic Evidence for a New Orangutan Species," Current Biology 27 (November 20, 2017): 1-12.
The Tapanuli orangutan is found south of Lake Toba in northern Sumatra in the Tapanuli Forest. The other Sumatran orangutan species--P. abelii--is found north of Lake Toba. The third orangutan species--P. pygmaeus--is found in Borneo. Orangutans in the wild are not found anywhere else in the world.
The Tapanuli orangutan has been found to be both morphologically and genomically distinct from the other two species. This analysis also suggests that the Tapanuli orangutan was the first orangutan species to arrive in Sumatra about three and a half million years ago from mainland Asia.
As I have indicated in a previous post a few years ago, I am sure that Jean-Jacques Rousseau would have been fascinated by these studies, because he inferred from some reports about apes in the wild that savage man in the state of nature was actually an orangutan as "a sort of middle point between the human species and the baboons." He looked forward to the time when scientists would travel the world to study the ape ancestors of human beings to understand the evolutionary history of humanity in the state of nature.
Rousseau would have discovered, however, that these modern studies deny his claim that the earliest human ancestors were utterly solitary animals, and thus "man is naturally good," because solitary individuals free from any dependence on others have no motive to be wicked. In fact, orangutans have a complex social life organized around the social bond between mothers and their offspring and a dominant adult male.
Here, then, is an example of how a claim in political philosophy--Rousseau's account of an asocial state of nature--can be refuted by the empirical science of evolutionary biology.
Recently, Nelson Lund--in his book Rousseau's Rejuvenation of Political Philosophy: A New Introduction (New York: Palgrave Macmillan, 2016)--has tried to defend Rousseau's position as confirmed by modern primatology and anthropology. He concludes: "Orangutans live much like man in Rousseau's pure state of nature; gorillas generally live in patriarchal family bands, much as Rousseau imagines man must have lived after the 'first revolution'; and chimpanzees are cooperative and contentious hunter-gatherers, like the people in Rousseau's 'nascent society'" (54).
Lund fails to see, however, that the complex social life of orangutans is not at all like the utterly solitary life of Rousseau's "nascent man" in the state of nature. I have elaborated this point in my chapter on Rousseau in Political Questions: Political Philosophy from Plato to Pinker (2015).
Rousseau's interest in orangutans as possibly revealing the ancestral origins of human evolution is well studied in Robert Cribb, Helen Gilbert, and Helen Tiffin's Wild Man from Borneo: A Cultural History of the Orangutan (Honolulu: University of Hawaii Press, 2017).