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 some big questions: How do humans relate to other primates, and how exactly did early humans move? Research by a professor at Texas A&M University can provide some 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 hand specimens representing recent humans, monkeys, and monkeys (measured from bones in museum collections around the world) to make comparisons about the type of movement behaviors used by the earliest hominids (fossil human relatives ). ).

The results provide clues to how early humans started walking upright and made similar movements that all humans perform today.

This discovery is described in a study published in the current issue of Science Advances

Bone shape reflects adaptation to certain habits or lifestyles – for example, the movement of primates – and by making connections between bone shape and behavior between living forms, we can draw conclusions about the behavior of extinct species, such as Ardi, that we can’t observe directly, ”said Prang.

In addition, we found evidence for a major evolutionary ‘leap’ between the type of hand that Ardi represented and all subsequent hominid hands, including those of Lucy’s kind (a famous 3.2 million year old, well-preserved skeleton found in the same area. This ‘evolutionary leap’ occurs at a critical time when hominids are adapting to a more humanoid form of upright walking, and the earliest evidence for the making of stone tools from hominids and the use of stone tools, such as marks on animal fossils discovered. “

Prang said the fact that Ardi represents an earlier stage in human evolutionary history is important because it may shed light on the kind of ancestor from which humans and chimpanzees evolved.

“Our study supports a classic idea, first proposed by Charles Darwin in 1871, when he had no fossils or knowledge of genetics, that the use of the hands and upper limbs for manipulation occurred in early human relatives associated with walk upright, ”he said. . “The evolution of human hands and feet probably happened in a correlated way.”

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

“It may take us one step closer to explaining how and why people developed our upright gait,” said Prang.

He added that the great change in hand anatomy between Ardi and all later hominins occurs at the same time, roughly between 4.4 and 3.3 million years ago, and coincides with the earliest evidence of the loss of a gripping big toe in the human evolution. This also coincides with the earliest known stone tools and animal fossils marked with chippings.

He said it appears to be marking a major change in the lifestyle and behavior of human family members within this time frame.

“We propose that it involves the evolution of more advanced upright walking, allowing human hands to be adapted through the evolutionary process for improved manual manipulation, possibly with stone tools,” said Prang.