4.4 million-year-old skeleton could reveal how early humans began to walk upright

Evolutionary expert Charles Darwin and others have recognized a close evolutionary relationship between humans, chimpanzees, and gorillas based on their common anatomies, raising big questions: how humans relate to other primates and how did the first humans move? Research by a professor at Texas A&M University may provide some answers.

Thomas Cody Prang, assistant professor of anthropology, and his colleagues examined the skeletal remains of Ardipithecus ramidus (“Ardi”), dated 4.4 million years old and found in Ethiopia. One of Ardi’s hands was exceptionally well preserved.

The researchers compared the shape of Ardi’s hand to hundreds of other hand specimens depicting recent humans, apes, and apes (measured from bones in museum collections around the world) to make comparisons on the type of locomotor behavior used by early hominids (fossil human parents).

The results provide clues as to how early humans began to walk upright and do similar movements that all humans perform today.

This discovery is described in a study published in the current issue of Scientific advances.

“Bone form reflects adaptation to particular habits or lifestyles – for example the movement of primates – and by making connections between bone form and the behavior of living forms, we can make inferences about behavior.” extinct species, like Ardi, that we can’t observe directly, says Prang.

“Additionally, we found evidence of a great evolutionary ‘leap’ between the type of hand represented by Ardi and all later hominid hands, including that of Lucy’s species (a famous well-preserved skeleton 3.2 million years old found in the same area This “ evolutionary leap ” occurs at a critical time when hominins are evolving into adaptations to a more human form of standing walking, and the earliest evidence of the making stone tools and the use of stone tools, such as cutting-marks on animal fossils, are discovered. “

Prang said that the fact that Ardi represents an earlier phase in the history of human evolution is important because it potentially sheds light on the type of ancestor that humans and chimpanzees evolved from.

“Our study supports a classic idea first proposed by Charles Darwin in 1871, when he had no fossils or understanding of genetics, that the use of the hands and upper limbs for manipulation is appeared in the first human parents in relation to standing walking, ”he said. . “The evolution of human hands and feet probably occurred in a correlated fashion.”

As Ardi is such an ancient species, it may retain some skeletal features that were present in the last common ancestor of humans and chimpanzees. If this is true, it could help researchers place the origin of the human line – in addition to walking upright – in a clearer light.

“This potentially brings us closer to an explanation of how and why humans have evolved our form of standing walking,” Prang said.

He added that the great change in the anatomy of the hand between Ardi and all subsequent hominids occurred at some point, around 4.4 to 3.3 million years ago, coinciding with the first evidence of the loss of a big toe in human evolution. It also coincides with the earliest known stone tools and animal fossils carved on stone.

He said this appears to mark a major change in the lifestyle and behavior of human parents during this time.

“We propose that this involves the evolution of a more advanced vertical walk, which has allowed human hands to be altered by the evolutionary process for improved manual handling, possibly involving stone tools,” Prang said.