Humans and Orangutan - Origins of Theory

Why Orangutans?
At first, and even second glance, orangutans do not look much like humans at all. They have very long arms, long body hair, and large vocal sacs in the male, and they live most of their lives within the canopy of trees. Not surprisingly, therefore, orangutans are widely thought of as having little to do with the immediate problem of human origins.

A closer look at orangutans reveals, however, a different possibility. When one looks for those features unique to humans and any one of the living great apes, it turns out that there are far more features found only in humans and orangutans than in humans and either chimpanzees, gorillas, or gibbons. Not only the number, but also the nature of many characters uniquely shared between humans and orangutans may have profound implications for how we look at both our evolutionary origins and ourselves.

The Piltdown Skull
The orangutan hypothesis may begin at any number of points, but perhaps the best illustration comes from an attempt to subvert science through the famous hoax known as the Piltdown skull. The hoax was successful for decades until chemical analysis in 1949 proved the bones were not ancient and then in 1953 it was found that molars of the lower jaw had been filed to fit to the teeth of the upper jaw. The skull was later determined to comprise a modern human (cranium) and the mandible of an orangutan – not a chimpanzee.

An Orangutan Jaw
The orangutan choice for the lower jaw of the Piltdown skull was necessary because orangutan teeth share one important feature with human teeth found in no other living ape – the presence of thick dental enamel. If thin enameled teeth of a chimpanzee were used the filing necessary for matching the lower and upper teeth would result in the inner dentine being exposed and thus reveal the hoax. Dental enamel is not only thin in all apes except humans and orangutans, but also all other primates with the isolated exception of two unrelated monkey species.onkey species.

Explaning Thick Enamel
The uniquely shared presence of thick dental enamel in humans and orangutans may be viewed in two different ways. The most widely held view is that the shared presence of thick enamel has nothing to do with humans and orangutans being more closely related to each other than other apes. Instead, it is argued that thick enamel evolved in the ancestor of all living and fossil great apes, but chimpanzees and gorillas reverted to the thin enamel condition of most monkeys. This theory is proposed on the assumption that chimps and gorilla are more closely related to humans than orangutans.

An alternative possibility is that thick dental enamel is present in humans and orangutans because they are more closely related to each other than other apes, and this condition was present in a common ancestor not shared with chimpanzees or gorillas. A test of this proposition would be the extent to which other characters may show the same pattern of relationships, and whether this pattern is better supported than characters uniquely shared between humans and chimpanzees or African apes. It is in addressing this question that the possibility of an entirely different model of human origin and evolution emerges.

Human and Orangutan Characters
To propose an evolutionary hypothesis at total variance with a universally accepted view is a very risky venture in a discipline that is very resistant to change. In the study of human evolution this is particularly true where the story of human origins linked to the African apes has been the pervasive message for over a century. The threads of this tale went largely unchallenged until Jeffrey Schwartz, at the University of Pittsburgh, expounded his orangutan hypothesis in a 1984 issue of the journal Nature. In this article Schwartz first laid out evidence supporting the evolutionary relationship of humans and orangutans and questioned the generally accepted hegemony of genetic similarity linking humans with chimpanzees.

Selected References

Schwartz, J.H. (1984) The evolutionary relationships of man and orang-utans.
Nature 308, 501-505.

Schwarz, J.H. (1987) The Red Ape. Houghton Mifflin Company, Boston.

Schwartz, J.H. (1988) History, morphology, paleontology, and evolution. Orangutan
biology (ed. by J.H. Schwartz), pp. 59-85. Oxford University Press, New York.

Schwartz, J.H. (2001) A review of the systematics and taxonomy of Hominoidea:
history, morphology, molecules, and fossils. Ludus Vitalis 9, 15-45.

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