Humans more closely related to orangutans than chimps

Posted by Emma Woollacott

Pittsburg - New fossil analysis suggests humans share a common ancestor with orangutans rather than chimpanzees, contradicting DNA evidence.


Jeffrey H Schwartz, professor of anthropology in Pitt's School of Arts and Sciences, and John Grehan, director of science at the Buffalo Museum,  scrutinized the hundreds of physical characteristics often cited as evidence of evolutionary relationships among humans and other great apes, and picked 63 that were unique within this group.


Of these, they found that humans shared 28 unique physical characteristics with orangutans, compared to only two with chimpanzees, seven with gorillas, and seven with all three apes. Gorillas and chimpanzees shared 11 unique characteristics.


Schwartz and Grehan then examined 56 features uniquely shared among modern humans, fossil hominids and fossil apes. They found that orangutans shared eight features with early humans and Australopithecus and seven with Australopithecus alone.


But their conclusion that humans are more closely related to orangutans than chimpanzees directly contradicts evidence from molecular analyses that links humans to chimpanzees.


The researchers claim that those molecular comparisons are often flawed. Molecular similarity doesn't necessarily imply an evolutionary relationship, they say, molecular studies often exclude orangutans, and molecular data that contradict the idea that genetic similarity denotes relation is often dismissed.


Schwartz and Grehan have support from other researchers in the field. "They have good morphological evidence in support of their interpretation,"  said paleoanthropologist Peter Andrews, a past head of Human Origins at the London Natural History Museum.


And Malte Ebach, a researcher at Arizona State University's International Institute for Species Exploration, commented, "Palaeoanthropology is based solely on morphology, and there is no scientific justification to favor DNA over morphological data. Yet the human-chimp relationship, generated by molecular data, has been accepted without any scrutiny."


Schwartz and Grehan describe theories that African apes had descended from earlier apes that migrated from Africa to Europe as "complicated and convoluted", and point to the absence of African ape fossils more than 500,000 years old.


They do acknowledge that early human and ape fossils are largely found in Africa, whereas modern orangutans are found in Southeast Asia. To account for this, they propose that the last common human-orangutan ancestor migrated between Africa, Europe, and Asia at least 12 million years ago. Plant fossils suggest that forests once extended throughout southern Europe, Central Asia and China, and Schwartz and Grehan propose that the ancestral hominoid lived and roamed throughout this vast area; as ecosystems changed, they say, descendant hominoids became geographically isolated from one another.

The research is published in the Journal of Biogeography.