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Tarzan swinging from tree to tree may seem like a Hollywood attempt to imagine the lives of primitive men, but new findings suggest that our ancient ancestors were indeed swingers.
The study apparently resolves a long-standing scientific debate about our ancestor’s ability to brachiation – the ability to swing from tree branches using only one’s arms. Before this ancestor saw an evolutionary shift towards using hands for tools and legs for walking, he likely walked on the ground and slipped on canopies.
What’s up – Research published Wednesday in the journal Scientific advances suggests the last common ancestor of hominids – a category of great apes that includes chimpanzees, gorillas, orangutans and humans – climbed and swayed in trees.
“Our results support the idea that humans and chimpanzees evolved from an ancestor that had similarities to modern apes in their locomotor adaptation,” says lead author Thomas C. Prang, assistant professor at Texas A&M University. Reverse.
A little background – Most scientists recognize that the very dexterous human hand appears to differ in shape and form from the hands used by primates to swing from trees.
However, this evidence gave rise to a contested hypothesis: Humans evolved from a quadrupedal ancestor who used all four limbs to move around the ground, rather than a bipedal ancestor hanging from trees.
Proponents of this hypothesis believe that the last common ancestor was more “ape-like” and less like, say, chimpanzees or bonobos.
The researchers in this study were skeptical of the idea and wanted to test its merits.
How they did it – The researchers used a sample of more than 400 specimens, including both living primates and ancient hominoid fossils.
First, the researchers analyzed ancient hand bones of Ardipithecus ramidus, which believers in the contested hypothesis use to support their idea regarding a last common quadrupedal ancestor. Ardipithecus ramidus is a human ancestor who lived almost 4.4 million years ago. Our understanding of this is mainly linked to a partial skeleton discovered in 2009, nicknamed “Ardi”.
The initial interpretation of this hand suggested that the last common ancestors of humans and chimpanzees used a form of locomotion called “climbing over branches,” explains Prang.
He doubts this interpretation for a reason: monkeys and lemurs are the only primates to use climbing above branches, and their much smaller bodies use external tails to help them climb trees – unlike the subject. of their study.
“The deduction of adaptations” above the branch “in Ardipithecus is somewhat problematic as it is the size of a chimpanzee and does not have an external tail [like all apes and humans]”Prang said.
To test it, Prang and his colleagues reconstructs the evolution of the hominin hand and how it adapted to ancient environments.
What they found – The results showed that Ar. Ramidus was most similar to chimpanzees, bonobos, and orangutans compared to “non-suspensive” monkeys. Overall, they compared the specimen to a sample of 53 species of anthropoid primates.
Ar. Ramidus had these suspensive traits – which allowed them to swing from tree branches – before a significant evolutionary change occurred with Homo (human) lineages and Australopithecus, an ancient ancestor of hominins, which includes humans and chimpanzees.
“The hand of Ardipithecus suggests that the last common ancestor of humans and chimpanzees was adapted to climb tree trunks and hang the body under branches, ”says Prang.
The study, in turn, is designed as a demystification of the previous hypothesis suggesting that hominins evolved from an ancestor “with a generalized hand that lacked suspensive adaptations”.
According to Prang, the study also indicates an important evolutionary step related to the development of the use of the tools.
“We show a major evolutionary leap in the hand of Ardipithecus and all subsequent hominids which coincide with the loss of tree climbing adaptations in the foot and the earliest known stone tools and animal fossils marked by stone tools, ”says Prang.
This finding supports the idea that Ar. Ramidus has shown an early form of bipedalism – or the ability to walk upright on two legs – which helps us understand how human hands and feet evolved.
“Our study provides some support for the hypothesis that human hands and feet have ‘co-evolved’, which previous studies have suggested based on model comparisons of hand / foot trait relationships and simulations. evolutionary, in humans and chimpanzees, ”Prang said.
Dig into the details – The researchers’ new findings relate to the work of more historical evolutionary researchers.
“Our analysis is much more consistent with what people like Thomas Henry Huxley and Sir Arthur Keith proposed in the late 19th and early 20th centuries based on anatomical comparisons between humans and apes,” says Prang.
The most notable of these historians is Charles Darwin, the father of evolution. Prang links Darwin’s work to their findings on bipedalism in the ancient specimen, which can help explain human evolution.
“The classic idea attributed to Darwin is that bipedalism ‘freed the hands’ from their primary role in quadrupedal locomotion, which allowed natural selection to push the anatomy of the hand in a new direction. [directly or indirectly] related to manual dexterity, perhaps useful for crafting and using stone tools, ”explains Pran.
Why is this important – According to the study, these findings “resolve a long-standing debate about the role of suspension in human ancestry.”
Alexandros Karakostis, an expert in hand biomechanics not affiliated with the study, describes the findings at Reverse as “very intriguing”. It provides a robust response to “a heated debate,” says Karakostis – although it is a debate that should continue.
“Against this background, this new study identifies suspensive adaptations in the 4.4 million-year-old hand remains of Ardipithecus ramidus, suggesting that the morphology of the human hand may have emerged from an evolutionary change between Ardipithecus and Australopithecus,” he says.
And after – In the future, the study team wishes to examine the Ardipithecus put back in more detail.
Ameline Bardo, a postdoctoral research associate at the University of Kent not affiliated with the study, agrees that more detailed analysis of the bones of the hand would be needed to “better understand the links between the shape and function of her hand” . This analysis, says Bardo Reverse, can contribute to an understanding of the movements of the ancient creature.
Overall, Bardo views the study as “very well done” and contributes to the idea that “the early hominins evolved from an ancestor with a varied positional repertoire including suspension and vertical climbing.”
The study team is very excited to explore the implications of the article for the evolution of great apes and humans.
“While it is true that humans and chimpanzees evolved from an ancestor resembling African apes, this implies that each line of African apes evolved at different rates,” says Prang.
“It will be important to reflect on the evolutionary histories of African ape populations and how the evolutionary process may have shaped their anatomy and behavior over the past millions of years.”
Abstract: The morphology and positional behavior of the last common ancestor of humans and chimpanzees is critical to understanding the evolution of bipedalism. Anatomical research in the early 20th century supported the idea that humans evolved from a suspensive ancestor somewhat resembling apes. However, the 4.4 million year old hominin hand Ardipithecus ramidus provides evidence that the hominid hand was derived from a more generalized form. Here, we use comparative morphometric and phylogenetic methods to show that Ardipithecus retains suspension-adapted hand morphologies shared with chimpanzees and bonobos. We identify an evolutionary change in the morphology of the hand between Ardipithecus and Australopithecus which renews the questions on the coevolution of the manipulation capacities of hominids and the obligatory bipedalism initially proposed by Darwin. Overall, our results suggest that early hominids evolved from an ancestor with a varied positional repertoire including suspension and vertical climbing, directly affecting the viable range of hypotheses on the origin of our lineage.
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