New evidence underscores the theory of human origin that suggests humans most likely share a common ancestor with orangutans, according to research from the University of Pittsburgh and the Buffalo Museum of Science. Reporting in the June 18 edition of the Journal of Biogeography, the researchers reject as “problematic” the popular suggestion, based on DNA analysis, that humans are most closely related to chimpanzees, which they maintain is not supported by fossil evidence.
Jeffrey H. Schwartz, professor of anthropology in Pitt’s School of Arts and Sciences and president of the World Academy of Art and Science, and John Grehan, director of science at the Buffalo Museum, conducted a detailed analysis of the physical features of living and fossil apes that suggested humans, orangutans, and early apes belong to a group separate from chimpanzees and gorillas.
They then constructed a scenario for how the human-orangutan common ancestor migrated between Southeast Asia—where modern orangutans are from—and other parts of the world and evolved into now-extinct apes and early humans. The study provides further evidence of the human-orangutan connection that Schwartz first proposed in his book The Red Ape: Orangutans and Human Origins (Westview Press, 2005).
Schwartz and Grehan scrutinised the hundreds of physical characteristics often cited as evidence of evolutionary relationships among humans and other great apes—chimps, gorillas, and orangutans—and selected 63 that could be verified as unique within this group (i.e., they do not appear in other primates). Of these features, the analysis found that humans shared 28 unique physical characteristics with orangutans, compared to only two features with chimpanzees, seven with gorillas, and seven with all three apes (chimpanzees, gorillas, and orangutans). Gorillas and chimpanzees shared 11 unique characteristics.
Schwartz and Grehan then examined 56 features uniquely shared among modern humans, fossil hominids—ancestral humans such as Australopithecus—and fossil apes. They found that orangutans shared eight features with early humans and Australopithecus and seven with Australopithecus alone. The occurrence of orangutan features in Australopithecus contradicts the expectation generated by DNA analysis that ancestral humans should have chimpanzee similarities, Schwartz and Grehan write. Chimpanzees and gorillas were found to share only those features found in all great apes.
Schwartz and Grehan pooled humans, orangutans, and the fossil apes into a new group called “dental hominoids,” named for their similarly thick-enamelled teeth. They labeled chimpanzees and gorillas as African apes and wrote in Biogeography that although they are a sister group of dental hominoids, “the African apes are not only less closely related to humans than are orangutans, but also less closely related to humans than are many” fossil apes.