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August 20, 2006
My Ancestor Was an Ape. But In What Ape Line?
Dienekes' Anthropology Blog reports on a paper by Jeffery Schwartz that argues that we are more closely related to Pongo, orangutans, than to Pan troglodytes, chimpanzees, as is usually thought. Dienekes also has a very cute composite picture of a chimp and an orangutan.
Schwartz bases his argument largely on morphology. Of the DNA evidence he says,
It is now widely accepted that DNA sequence similarities not only support the African ape connection, but also demonstrate that we share a unique common ancestor with chimpanzees, followed by the gorilla, and lastly by the orangutan. . . . There remains, however, a paradoxical problem lurking within the wealth of DNA data: our morphology and physiology have very little, if anything, uniquely in common with chimpanzees to corroborate a unique common ancestor. Most of the characters we do share with chimpanzees also occur in other primates, and in sexual biology and reproduction we could hardly be more different. It would be an understatement to think of this as an evolutionary puzzle. The usual solution is to invoke the loss of the African ape features following our divergence from the common ancestor. This ad hoc solution might be plausible if it were not for the incongruous fact that humans share many unique features with the orangutan. This ape is not only the least similar to humans in DNA sequence similarity, but the very ape nearly universally considered the most primitive of all living great apes. [references deleted]
He looks at a number of features where he claims humans and orangutans are similar or at least closer to each other than humans are to chimpanzees: Limb Development and Morphology, Skull Morphology, Molar Morphology, External Morphology, Reproductive Biology, Internal Anatomy, Behavior and a few miscellaneous features.
This is not a new idea but it is very much a minority report. And it is not without fairly obvious problems. For example, when discussing external morphology he says,
Largest distance between nipples (character 22): As an average percentage of chest width, the distance is greater in humans (71%) and orangutans (90%) compared with chimpanzees (52%), gorillas (46%), gibbons (32%), siamangs (8%), and macaques (40%). The hylobatid species were not specified, and although Schultz (1936) measured only one monkey group, the human-great ape comparison is probably robust since monkeys have a narrower rib cage than hominoids.
That puts humans nearly midway between chimpanzees and orangutans: 18 percentage points between humans and orangutans and 19 percentage points between humans and chimpanzees. I'd hate to have one of my hypotheses live or die on one percentage point. But then I'm not a biologist politician.
Schwartz discusses dozens of features, most of which I am not competent to evaluate. Heck, I may not be competent to evaluate the one which I did try to evaluate.
Of all this Dienekes writes,
This is certainly a controversial thesis, and I am not holding my breath that the consensus will change any time soon, but we should definitely give it a proper hearing. In the very least, if morphology and genetics don't agree, we should not a priori assign precedence to genetics. Genetics is "harder" evidence for relatedness than morphology; on the other hand, genes can't be studied for fossil hominids dating to millions of years in the past.
I'm not holding my breath either.
There is one thing I think must be made very clear. This is the way science does its work, putting forth evidence and attempting to find coherent explanations for that evidence. The fact these explanations sometimes disagree should give no comfort to creationists of any stripe. Both the consensus human/chimpanzee relationship explanation and the suggested human/orangutan relationship are based on modern evolutionary theory and neither would make any sense without that theory. Creationists often protest that they are not taken seriously. Well, if creationists would layout their evidence and provide the kind of discussion seen in Schwartz paper, they would be taken seriously. The problem is that creationists have no evidence, while Schwartz certainly has some. So the scientific community will give his paper a lot more consideration than they would give to evidence free creationists papers.
Posted by Duane Smith at August 20, 2006 6:27 PM | Read more on Paleoanthropology |
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