For a half century, the iconic “Lucy” fossil species, Australopithecus afarensis, has held the title of being the most likely direct ancestor of all humans.
But as the list of ancient human relatives has grown and more fossils have been discovered, Lucy’s position has increasingly been called into question. Now, a key paper published last month in the journal Nature could overturn that theory entirely, some scientists say.
They argue that,given the new evidence,an older species,Australopithecus anamensis, was our direct ancestor,not Lucy.
The proposal has revealed intense disagreements in the field. Some say A. anamensis is our direct ancestor, others argue that we don’t know which Australopithecus species we descended from, and still others say the new analysis doesn’t shake up the human family tree at all.
The new discovery is “not altering our picture of human evolution in any way,in my opinion,” Zeray alemseged, a paleoanthropologist and professor of organismal biology and anatomy at the University of Chicago who was not involved in the new study, told Live science.
Either way,a resolution might not come until more fossils are found.An iconic species
Understanding the roots of the debate requires going back a century. In 1925, Raymond Dart announced the discovery of the “Taung Child,” a young Australopithecus africanus, in South Africa. This was the first hominin fossil found that suggested humans might have evolved in Africa, rather than in Europe or Asia, as many scientists believed at the time.
But it wasn’t until 1974, when Donald Johanson and colleagues discovered the Lucy fossil in Ethiopia, that Australopithecus afarensis became the frontrunner for our direct ancestor. Lucy was remarkably complete – about 40% of her skeleton was recovered – and showed that these early hominins walked upright.
The discovery of Lucy and other A. afarensis fossils led to the idea that this species was a transitional form between apes and humans, and that it gave rise to the genus Homo, which includes modern humans.
Though, A. afarensis wasn’t the first Australopithecus species to appear. That title belongs to A. anamensis,which lived about 4.2 million to 3.9 million years ago, while A. afarensis lived from about 3.9 million to 2.9 million years ago.
For decades, scientists thought that A. anamensis evolved into A. afarensis, and that Lucy’s species was the one that eventually led to us. But the new research challenges this view.
The new study focuses on a remarkably well-preserved A. anamensis cranium discovered in Ethiopia in 2016. By analyzing the shape of the cranium, the researchers argue that A. anamensis had a more human-like face than previously thought, and that it was more closely related to the ancestors of humans than A. afarensis.
In other words, the researchers propose that A. anamensis didn’t evolve into A. afarensis. Instead, A. afarensis branched off from A. anamensis, and it was A. anamensis that continued to evolve and eventually gave rise to the genus Homo.
This new interpretation of the fossil record has sparked a heated debate among paleoanthropologists. Some experts agree with the researchers, while others remain skeptical.
“This is a very critically important paper that raises some challenging questions,” said Lucy May Not Be Our Direct Ancestor, New Fossil Evidence Suggests
For decades, the hominin fossil record seemed to cement Australopithecus afarensis – the species of the famous “Lucy” – as our direct ancestor. An assessment of the evolutionary relationships among hominin fossils uncovered until that point suggested Lucy’s species gave rise to the genus Homo. In that family tree, A. africanus was demoted from our ancestor to a more distant cousin. As more australopithecines have been unearthed, the Australopithecus family tree has become bushier and more tangled, complicating the picture of who we may have descended from. But for many anthropologists Lucy’s species still reigns, eventually giving rise to the lineage from which modern humans evolved. Then the new Nature paper was published. Researchers had unearthed new fossil fragments and tied them to a previously discovered, enigmatic 3.4 million-year-old fossil known as the “Burtele foot.” The new tooth and jaw fragments allowed anthropologists to ascribe the foot, for the first time, to a little described and controversial species – Australopithecus deyiremeda, a tree-climbing ancient human relative that walked upright on two legs and lived alongside Lucy’s species 3.5 million to 3.3 million years ago at the Woranso-Mille site in Ethiopia. For Fred Spoor, a professor of evolutionary anatomy at University College London who was not involved in the A newly analyzed fossil skull is stirring up debate among anthropologists about the origins of the human family tree. the skull, belonging to Australopithecus prometheus – a hominin species known from the Taung Child fossil discovered in South Africa in 1924 – suggests that A. prometheus may have been a close relative, and perhaps even a direct ancestor, of the Homo genus, which includes modern humans. this challenges the long-held belief that Australopithecus afarensis, the species of the famous “Lucy” fossil, was the sole ancestor of all later hominins. “It is certainly possible that A. prometheus was directly ancestral to Homo,” said lauren Schroeder, a paleoanthropologist at the University of Toronto Mississauga and lead author of the new study, published feb. 7 in the journal Nature Ecology & Evolution. “Lucy’s species is still a candidate, but no longer the candidate.” The research team used high-resolution CT scans to create a detailed reconstruction of the A.prometheus skull,revealing features in its cranial base that are more similar to those of Homo than to A. afarensis. These features relate to brain size and the positioning of the foramen magnum – the hole in the skull where the spinal cord connects – suggesting a more human-like posture and potentially greater cognitive abilities. Though, the findings are not without controversy. Fred Spoor, a paleoanthropologist at University College London, who was not involved in the study, wrote that, “if this analysis is correct, A. afarensis will lose its iconic status as the ancestor of all later hominins,” probably including us, Spoor wrote in an accompanying commentary about the recent research. But other anthropologists are hotly divided on the implications of the new paper. Some Live Science spoke to thought Spoor’s conclusions where plausible, while other experts said they were “far-fetched” and “a stretch, to put it mildly.” Because the existing fossil record in East Africa goes much further back in time than the current South African record,many believe the Homo genus arose in East Africa. Currently the oldest known Homo fossil is a 2.8 million-year-old jawbone from Ethiopia, but models estimate the genus would have actually emerged around 0.5 million to 1.5 million years earlier. This is older than many of the earliest South African hominin fossils, which were found thousands of miles away. That “would make it unlikely that any of those are the direct ancestor,” Carol Ward, the Curators’ Distinguished Professor of pathology and anatomical sciences at the University of Missouri, told Live Science. For many, the most likely candidate for an East African ancestor is still Lucy’s species, A. afarensis,which lived in modern-day Ethiopia,Tanzania and Kenya from around 3.9 million to 3 million years ago. This wide geographic distribution and persistence for almost a million years means it had many opportunities to give rise to other species across Africa, Alemseged said. Scientists in the “Lucy” camp argue that A. afarensis‘ fully upright mode of walking, broad diet, use of early stone tools and wide geographic range constitute strong evidence for Lucy’s ancestral position in the human family tree. This makes Spoor’s claim that Lucy’s species wasn’t our direct ancestor a big one. But he isn’t alone in this view. A newly discovered fossil, Australopithecus deyiremeda, is prompting scientists to re-evaluate the established narrative of human evolution, specifically challenging the long-held belief that “Lucy” (Australopithecus afarensis) was a direct ancestor to homo, the genus that includes modern humans. The findings, published in the journal Nature, suggest a more complex and branching evolutionary history than previously understood. The fossil,unearthed in Ethiopia’s Afar region,dates back approximately 3.8 million years – around the same time as Lucy. Its characteristics, however, differ significantly from A. afarensis, indicating a greater degree of diversity among early hominins than previously recognized.This discovery supports the idea that multiple hominin species coexisted and potentially interbred in Africa between 3.5 and 2 million years ago. “Early Homo could have emerged from a broader, pan-African pool of australopith diversity,” explained Dr. Carol Ward, a paleoanthropologist at the University of Toronto Mississauga who was not involved in the study. She described our evolutionary history as “more like a braided stream, with species separating and then recombining, and less like a straight evolutionary line.” https://www.livescience.com/lucy-human-ancestor-debate the debate surrounding Lucy’s position in the human family tree is far from settled, even among the researchers involved in the new discovery. While Yohannes Haile-Selassie, a paleoanthropologist and director of Arizona State University’s Institute of Human Origins, led the research on A.deyiremeda, he continues to believe A. afarensis remains the most likely ancestor to Homo. https://search.asu.edu/profile/4011149 Haile-Selassie argues that A. deyiremeda and another species,Australopithecus africanus,possess more primitive traits,such as feet adapted for climbing trees,which are inconsistent with a direct lineage to humans.He points to Lucy’s species having more human-like feet as evidence supporting its ancestral role. https://www.livescience.com/lucy-human-ancestor-debate However, other researchers, like study co-author Stephanie Prang, support the idea that Lucy’s species is being “dethroned” as our direct ancestor. The discovery of A. deyiremeda adds to a growing body of evidence suggesting a more complex evolutionary landscape. The fossil record is incomplete, and the search for a definitive “missing link” may prove futile. As Dr. Ward notes, “We will almost certainly never know who our direct ancestor is – and the more we learn about human evolution and how diverse our past was, the more elusive that ancestor becomes.” Despite the uncertainty, researchers remain optimistic about unraveling the mysteries of our past. “Even though we may never know which one was our ancestor, we can still piece together much of what that ancestor may have been like,” Ward concluded. The ongoing discoveries and debates continue to refine our understanding of the intricate and interesting story of human evolution. Related readingNew Fossil Discovery Challenges ‘Lucy’s’ Place as Our Ancestor
New Fossil Discovery Challenges Lucy’s role as Direct Human Ancestor