New analysis shows that human ancestors were "rooted"

African great apes have adapted to life on the ground. This discovery indicates that man has evolved from an ancestor not limited to trees or other elevated habitats. The analysis adds a new chapter to the evolution, shedding additional light on what preceded human bipedalism.

African great apes have adapted to life on the ground. This discovery indicates that man has evolved from an ancestor not limited to trees or other elevated habitats. The analysis adds a new chapter to the evolution, shedding additional light on what preceded human bipedalism.

"Our unique form of human locomotion came from an ancestor who evolved in the same way as the living African apes: chimpanzees, bonobos, and gorillas," says Thomas Prang, PhD candidate in the Department of Anthropology. New York University and author of the study. , which appears in the newspaper eLife. "In other words, the common ancestor we share with chimpanzees and bonobos was an African monkey who probably had adaptations to life on the ground in any way and frequency that this is."

The way humans walk – the progressive bipedalism – is unique among all living mammals, an attribute resulting from multiple changes over time.

"The human body has been dramatically altered by evolutionary processes over the last million years to make us better walkers and runners," notes Prang.

Much of this change is evident in the human foot, which has evolved to become a propulsive organ, with a big toe unable to grip the monkeys and a spring-like, energy-saving arch that extends from the Forward towards the back.

These traits raise a long-studied but unresolved question: "What type of ancestor has the human foot evolved?

in the eLife Prang, a researcher at the Center for the Study of Human Origins at the University of New York, has focused on the fossil species Ardipithecus ramidus ("Ardi"), ancestor Ethiopia 's 4.4 million year old human – more than a million years older than the well "Lucy", a known fossil. Ardi's bones were first publicly revealed in 2009 and have been the subject of debate ever since.

In his research, Prang determined the relative length proportions of several bones in the skeleton of the primate foot to assess the relationship between species movements (locomotion) and their skeletal characteristics (morphology). In addition, relying on Ardi's fossils, he used statistical methods to reconstruct or estimate the appearance of the common ancestor of humans and chimpanzees.

Here, he found that African monkeys clearly show that they are adapted to life on the ground. The results also reveal that the Ardi foot and the estimated morphology of the last common human-chimpanzee ancestor are very similar to these species of African monkeys.

"As a result, humans evolved from an ancestor who had adaptations to life on the ground, perhaps not so different from those found in African monkeys," Prang concludes. "These results suggest that human bipedalism was derived from a locomotion pattern similar to that of living African monkeys, which contrasts with the original interpretation of these fossils."

The original interpretation of the Ardi foot fossils, published in 2009, suggested that his foot was more like a monkey than a chimpanzee or a gorilla. The implication of this interpretation is that many of the features shared by living great apes (chimpanzees, bonobos, gorillas and orangutans) in their foot and elsewhere must have evolved independently in each lineage – at one time and at a time. different place.

"Humans are part of the natural world and our locomotor adaptation – biped – can not be understood outside of its natural evolutionary context," Prang observes. "Large-scale evolutionary changes do not seem to occur spontaneously, but are rooted in deeper stories revealed by the study of the fossil record.

"The study of the Ardi fossil shows that the evolution of our own adaptation to life on the ground – bipedalism – was preceded by an adaptation to life on the quadruped ground to the common ancestors we share with African monkeys. "