The origin of human bipedalism, the ability to walk on two legs, is one of the great debates in science today. For decades, scientists have wondered what the last common ancestor we share with us was like. chimpanzees and its characteristics. Now an ankle bone has ended up giving us the key we were looking for to rethink everything what we knew about our ancestors.
The study. Published in Communications Biology and as the protagonist a 4.4 million year old ankle bone that belonged to a Ardipithecus ramidus. a hominid which was discovered in Ethiopia and which gives us many data about the history of human evolution.
And this is because the conclusion is surprising: the ankle of this ancient hominid has surprising similarities with those of modern chimpanzees and gorillas. Something that makes us think that humans evolve from an ancestor similar to African apes, which makes us wonder about how and why we began to walk upright.
The great debate. He Ardipithecus ramidusor “Ardi”, is essential in this case. It lived 4.4 million years ago and already displayed hominid characteristics, but combined primitive features such as a prehensile, ape-like big toe with human-derived features in the pelvis and skull. This is what suggests right now that an “early form of bipedalism” was used.
The key is in the morphology of the talus, which in Ardi resembles that of African apes more than that of any other fossil hominin analyzed. The objective in this case is to know how our ancestors moved on the surface, but they also climbed trees vertically.
This suggests that it made use of both early bipedalism and skills typical of arboreal life, placing Ardi in an intermediate position between Australopithecus and the great apes. And this bone is the fundamental key to knowing how the evolution to bipedalism took place.
The challenge. This finding broadly challenges the traditional model of human evolution, which assumed that the last common ancestor with chimpanzees was a generalist and arboreal ape, alien to terrestrial life and bipedalism. New evidence indicates that humans most likely evolved from an African ancestor specialized in vertical climbing and also had plantigrade terrestrial locomotion. That is, with the soles of the feet completely supported like current gorillas and chimpanzees. A true hybrid between the two automotive models.
The authors maintain that several lineages (humans, chimpanzees, bonobos and gorillas) share a past adapted to mixed life between trees and soil. The subsequent evolution of bipedalism would have been built on that basis, little by little modifying the anatomy and locomotor abilities to stop climbing trees and move on to what we now all use in our daily lives.
Its implications. The morphometric data of the ankle of Ardipithecus demonstrate the presence of a structure designed to “push” when walking and improve balance, but without completely losing the ability to grip. The evolutionary process towards complete bipedalism was much more gradual and less linear than what had originally been proposed by experts.
Furthermore, the most recent studies not only focus on the talus, but also on the metatarsus and pelvis, confirming that Ardi could walk upright during his short journeys and return to trees to climb and take shelter. This duality is key to understanding how our ancestors adapted to different environments and ecological pressures.
What changes. The hybrid anatomy of Ardipithecus ramidus dismantles the chimpanzee ancestor myth, and presents a new branch on our human evolutionary tree. Far from being a rarity, Ardi represents an example of evolutionary transition and the complexities that may exist in the origins of our species. Thus, scientists propose abandoning this concept of a straight line in evolution and embracing an adaptive mosaic between different species.
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