THE LAST SHARED ANCESTOR OF APES AND HUMANS
7 million years ago
|This is a cast/reconstruction of Sahelanthropus tchadensis, an extinct hominid species dated to about 7million years ago. It is debated as to whether it may be the first hominid after the chimp/hominid split. There has been no postcrania (skeletal material below the skull) found, but based on the position of the opening at the base of the skull, it has been suggested that Sahelanthropus may be bipedal. More fossils are needed to elucidate this controversy.
Credit: Photo by Kathy Schick, courtesy of the Stone Age Institute. All rights reserved.
Genetic evidence suggests that humans and our closest relatives, the African apes (gorillas, chimpanzees, and bonobos or “pygmy chimpanzees”) shared a common ancestor but then went down different evolutionary pathways (an evolutionary “split” or branch) around seven million years ago. The further back we go in the human fossil record, the more these forms are ape-like.
Unfortunately, we have very few fossils between 10 and 7 million years ago, so that this hypothetical last common ancestor is still elusive. As previously mentioned, animals that lived in dense, wet tropical forests are not great candidates for fossilization, as these damp and often acid conditions are not conducive to bone fossilization. But the actual event, this divergence between the human and ape line, is a critical one in our evolutionary history.
|This is another view of S. tchadensis, nicknamed Toumaï (“hope of life” in the local Dazaga language of Chad). Some scientists believe that it may be ancestral to neither chimp nor human, but may be a lineage that was related to chimps or gorillas. There is still no consensus.
Credit: Photo by Didier Descouens, courtesy of Wikimedia.
HOW DO WE KNOW?
Our knowledge of this last common ancestor and its approximate age is primarily known from the genetic evidence of modern apes and humans, and by the examination of the fossil record of apes prior to 10 million years ago as well as the fossil record of the earliest hominins is the last 6 million years.
WHY SHOULD I CARE?
The divergence of early humans (hominins) and the African apes marked a major departure in our evolutionary history that would lead to upright walking ancestors and related forms moving from the dense tropical forests to more wooded and open grassland environments.
This is an excellent website on human origins from the Smithsonian.
This website contains a countdown of the top 10 missing links in human evolution with pictures and basic information about each.
This is a Nature News article, “Ancient human ancestor had feet like an ape.”
This is a brief article about Sahelanthropus tchadensis.
A brief article from BBC News about fossils suggests that hominids were bipedal dating to six million years old.
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