Fossils May Look Like Human Bones: Biological Anthropologists Question Claims for Human Ancestry
ScienceDaily (Feb. 16, 2011) — "Too simple" and "not so fast" suggest biological anthropologists from the George Washington University and New York University about the origins of human ancestry. In the upcoming issue of the journal Nature, the anthropologists question the claims that several prominent fossil discoveries made in the last decade are our human ancestors. Instead, the authors offer a more nuanced explanation of the fossils' place in the Tree of Life. They conclude that instead of being our ancestors the fossils more likely belong to extinct distant cousins.
An orangutan. Ramapithecus, a species of fossil ape from south Asia, was mistakenly assumed to be an early human ancestor in the 1960s and 1970s, but later found to be a close relative of the orangutan. Researchers conclude that instead of being our ancestors many fossils more likely belong to extinct distant cousins. (Credit: iStockphoto/Derek Dammann)
"Don't get me wrong, these are all important finds," said co-author Bernard Wood, University Professor of Human Origins and professor of Human Evolution Anatomy at GW and director of its Center for the Advanced Study of Hominid Paleobiology. "But to simply assume that anything found in that time range has to be a human ancestor is naïve."
The paper, "The evolutionary context of the first hominins," reconsiders the evolutionary relationships of fossils named Orrorin, Sahelanthropus andArdipithecus, dating from four to seven million years ago, which have been claimed to be the earliest human ancestors. Ardipithecus, commonly known as "Ardi," was discovered in Ethiopia and was found to be radically different from what many researchers had expected for an early human ancestor. Nonetheless, the scientists who made the discovery were adamant it is a human ancestor.
"We are not saying that these fossils are definitively not early human ancestors," said co-author Terry Harrison, a professor in NYU's Department of Anthropology and director of its Center for the Study of Human Origins. "But their status has been presumed rather than adequately demonstrated, and there are a number of alternative interpretations that are possible. We believe that it is just as likely or more likely that they are fossil apes situated close to the ancestry of the living great ape and humans."
The authors are skeptical about the interpretation of the discoveries and advocate a more nuanced approach to classifying the fossils. Wood and Harrison argue that it is naïve to assume that all fossils are the ancestors of creatures alive today and also note that shared morphology or homoplasy -- the same characteristics seen in species of different ancestry -- was not taken into account by the scientists who found and described the fossils. For example, the authors claim that for Ardipithecus to be a human ancestor, one must assume that homoplasy does not exist in our lineage, but is common in the lineages closest to ours. The authors suggest there are a number of potential interpretations of these fossils and that being a human ancestor is by no means the simplest, or most parsimonious explanation....
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The evolutionary context of the first hominins
Bernard Wood & Terry Harrison
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Nature 470, 347–352 (17 February 2011) doi:10.1038/nature09709
Published online 16 February 2011
The relationships among the living apes and modern humans have effectively been resolved, but it is much more difficult to locate fossil apes on the tree of life because shared skeletal morphology does not always mean shared recent evolutionary history. Sorting fossil taxa into those that belong on the branch of the tree of life that leads to modern humans from those that belong on other closely related branches is a considerable challenge.
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