A 4.4-million-year-old skeleton could show how early humans moved and began walking upright, according to new research led by an anthropology professor at Texas A&M University.
Evolutionary expert Charles Darwin and others recognized a close evolutionary relationship between humans, chimpanzees, and gorillas based on their shared anatomy, raising some big questions: How did humans relate to other primates, and how exactly did the early humans move? Research by a Texas A&M professor may offer some answers.
Thomas Cody Prang, Associate Professor of Anthropology, and his colleagues examined the skeletal remains of Ardipithecus ramidus (“Ardi”), which date back to 4.4 million years ago, and were found in Ethiopia. One of Ardi’s hands was in very good condition.
The researchers compared the shape of Ardi’s hand with hundreds of other hand samples representing humans, apes, and modern apes (measured from bones in museum collections around the world) to make comparisons about the type of locomotor behavior used by early hominins (fossil human relatives).
The results provide clues about how early humans began walking upright and making similar movements that all humans do today.
This discovery is described in a study published in the current issue of Science advances.
“The shape of the bones reflects the adaptation to specific habits or lifestyles – for example the movement of primates – and by charting the links between bone shape and behavior between living forms, we can make inferences about the behavior of an extinct species, such as the Ardi, we can do so,” Prang R. observes directly.
In addition, we found evidence of a significant evolutionary ‘jump’ between the type of hand represented by Ardi and all the hands of later hominins, including those of the Lucy species (a famous, well-preserved 3.2 million-year-old skeleton that was found in the same area in the 1970s This “ evolutionary leap ” occurs at a critical time when hominins develop adaptations to a more human-like form of an erect walking, and the first evidence of stone tool manufacture for hominins and the use of stone tools, such as cut marks on animal fossils, have been discovered.
The fact that Ardi represents an early stage in the history of human evolution is important because it likely sheds light on the type of ancestor from which humans and chimpanzees arose, Prang said.
He said, “Our study supports a classic idea first proposed by Charles Darwin in 1871, when he had no fossils or understood genetics, that the use of hands and upper limbs to manipulate appeared in early human relatives in relation to straight walking.” . The development of hands and feet may have occurred in an interdependent manner.
Since Ardi is an ancient species, it may retain structural features that were present in the last common ancestor of humans and chimpanzees. If true, it could help researchers put the human ancestry – in addition to walking upright – in a clearer light.
“It will probably bring us one step closer to explaining how and why humans evolved our form of walking erect,” Prang said.
He added that the major change in the anatomy of the hand between Ardi and all subsequent hominins occurs sometime, roughly between 4.4 and 3.3 million years ago, coinciding with the first evidence of big toe loss in human evolution. This also matches the oldest known stone tools and animal fossils with stone markings.
He said it appeared to represent a major change in the lifestyle and behavior of human relatives during this time frame.
“We suggest that this include an evolution of more advanced upright gait, which enabled human hands to be modified by the evolutionary process to improve manual manipulation, and possibly with stone tools,” Prang said.
This research was funded by the Wenner Gren Foundation.
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