A 4.4 million-year-old skeleton could reveal how early humans started walking upright

Evolutionary expert Charles Darwin and others recognized a close evolutionary relationship between humans, chimpanzees, and gorillas based on their shared anatomy, which raised major questions: how are humans related to other primates, and exactly how did early humans move around? ? Research by a Texas professor at A&M University can provide answers.

Thomas Cody Prang, assistant professor of anthropology, and colleagues examined the skeletal remains of Ardipithecus ramidus (“Ardi”), dated to 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 with hundreds of other specimens of recent humans, apes, and apes (measured on bones in museum collections around the world) to make comparisons about the type of movement behavior used by the earliest hominins (fossil humans). . ).

The results give clues as to how early people started walking upright and make similar movements that all people perform today.

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

“Bone shape reflects the adaptation to certain habits or lifestyles – for example the movement of primates – and by drawing connections between bone shape and behavior between living forms, we can draw conclusions about the behavior of extinct species, such as Ardi, that we observe directly. , Prang said.

“In addition, we found evidence of a major evolutionary ‘leap’ between the kind of hand proposed by Ardi and all later hominin hands, including that of Lucy’s species (a well-known 3.2 million-year-old well-preserved skeleton that occurs in the same area in the 1970s.) This ‘evolutionary leap’ occurs at a critical time when hominin adaptations develop to a more humane form of upright walking, and the earliest evidence for the manufacture of stone aids and the use of stone tools, such as cut marks on animal fossils are discovered. “

Prang said that the fact that Ardi represents an earlier phase of the evolutionary history of man is important because it may shine on the kind of ancestor from which humans and chimpanzees evolved.

“Our study supports a classical idea that Charles Darwin proposed in 1871, when he had no fossils or understanding of genetics, that the use of the hands and upper limbs for manipulation in early human relatives appears to be related to upright walking, he said. . “The evolution of human hands and feet probably took place in a correlated way.”

Since Ardi is such an ancient species, it can retain skeletal features that are found in the last common ancestor of humans and chimpanzees. If true, it could help researchers shed more light on the origins of the human race – in addition to walking upright.

“It might bring us one step closer to an explanation for how and why people developed our form of upright walking,” Prang said.

He added that the great change in the anatomy of the hand between Ardi and all later hominins occurs at once, approximately between 4.4 and 3.3 million years ago, coinciding with the earliest evidence of the loss of a gripping big toe in human evolution. It also coincides with the earliest known stone tools and stone-cut animal fossils.

He said it was apparently a major change in the lifestyle and behavior of human family members within this period.

“We suggest that this includes the development of more advanced upright barrels, which could change human hands through the evolutionary process for improved manual manipulation, which may include stone tools,” Prang said.