Several prominent fossil discoveries made in the last 10 years have been claimed to be the ancestors of modern humans. In a new paper in the journal Nature, two American biological anthropologists question the simplicity of the claims, saying instead that the fossils are more likely great apes.
“Don’t get me wrong, these are all important finds,” said co-author Bernard Wood in a press release. “But to simply assume that anything found in that time range has to be a human ancestor is naïve.” Wood is a professor of human origins at George Washington University and director of its Center for the Advanced Study of Hominid Paleobiology.
Their paper looks at three fossils: the 6-million-year-old Orrorin, discovered in Kenya; Sahelanthropus, a partial skull unearthed in Chad and dated to 7 million years old; and Ardipithecus, or “Ardi” for short, discovered in Ethiopia and thought to have lived around 4 million years ago. Although Ardi was very different from what paleontologists had expected a human ancestor to look like, it was nonetheless claimed to be one.
The status of these fossils “has been presumed rather than adequately demonstrated,” said co-author Terry Harrison, a professor in the Department of Anthropology at New York University and director of its Center for the Study of Human Origins.
“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.”
In their paper, Wood and Harrison argue that assuming all fossils are the ancestors of creatures alive today is naïve. They also point out a number of limitations in the method that paleontologists use to analyze the relationships between species—in particular the issue of “homoplasy,” or physical traits that are present in unrelated species. A classic example is wings in birds and bats.
Homoplasy is a problem because scientists follow the assumption that the more similarities animals share with each other, the more closely related they are. In the fossil record, where often only parts of animals are preserved, these apparent similarities can lead to the wrong conclusions.
“Only a quarter of a century ago the palaeoanthropological community learned, or should have learned, a sobering lesson about how easily homoplasy can lead to misinterpretation,” Wood and Harrison write in their article.
They state the example of Ramapithecus, which was assumed in the 1960s and ’70s to be a human ancestor based on shared similarities in the shape of the skull, jaw and teeth, but was later interpreted as an orangutan-like ape.
They also discussed the case of Oreopithecus bambolii, a fossil ape from Italy that has many physical similarities to ancient humans, including in the teeth, jaw, skull, hips, and legs, which were used to claim it was a human ancestor. But, these characteristics are more easily explained as homoplasies, said Wood and Harrison.
Many of these physical traits are also found in Ardi, the researchers point out.
“Oreopithecus highlights the dangers inherent in uncritically assuming that shared similarities are a secure indication of relationship.”
While not making any specific claims, Wood and Harrison conclude by asking that paleoanthropologists “acknowledge the potential shortcomings of their data when it comes to generating hypotheses about relationships.”
“We urge researchers, teachers, and students to consider the published ... interpretations of these taxa as among a number of possible interpretations of the evidence.”
“Don’t get me wrong, these are all important finds,” said co-author Bernard Wood in a press release. “But to simply assume that anything found in that time range has to be a human ancestor is naïve.” Wood is a professor of human origins at George Washington University and director of its Center for the Advanced Study of Hominid Paleobiology.
Their paper looks at three fossils: the 6-million-year-old Orrorin, discovered in Kenya; Sahelanthropus, a partial skull unearthed in Chad and dated to 7 million years old; and Ardipithecus, or “Ardi” for short, discovered in Ethiopia and thought to have lived around 4 million years ago. Although Ardi was very different from what paleontologists had expected a human ancestor to look like, it was nonetheless claimed to be one.
The status of these fossils “has been presumed rather than adequately demonstrated,” said co-author Terry Harrison, a professor in the Department of Anthropology at New York University and director of its Center for the Study of Human Origins.
“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.”
In their paper, Wood and Harrison argue that assuming all fossils are the ancestors of creatures alive today is naïve. They also point out a number of limitations in the method that paleontologists use to analyze the relationships between species—in particular the issue of “homoplasy,” or physical traits that are present in unrelated species. A classic example is wings in birds and bats.
Homoplasy is a problem because scientists follow the assumption that the more similarities animals share with each other, the more closely related they are. In the fossil record, where often only parts of animals are preserved, these apparent similarities can lead to the wrong conclusions.
“Only a quarter of a century ago the palaeoanthropological community learned, or should have learned, a sobering lesson about how easily homoplasy can lead to misinterpretation,” Wood and Harrison write in their article.
They state the example of Ramapithecus, which was assumed in the 1960s and ’70s to be a human ancestor based on shared similarities in the shape of the skull, jaw and teeth, but was later interpreted as an orangutan-like ape.
They also discussed the case of Oreopithecus bambolii, a fossil ape from Italy that has many physical similarities to ancient humans, including in the teeth, jaw, skull, hips, and legs, which were used to claim it was a human ancestor. But, these characteristics are more easily explained as homoplasies, said Wood and Harrison.
Many of these physical traits are also found in Ardi, the researchers point out.
“Oreopithecus highlights the dangers inherent in uncritically assuming that shared similarities are a secure indication of relationship.”
While not making any specific claims, Wood and Harrison conclude by asking that paleoanthropologists “acknowledge the potential shortcomings of their data when it comes to generating hypotheses about relationships.”
“We urge researchers, teachers, and students to consider the published ... interpretations of these taxa as among a number of possible interpretations of the evidence.”
