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A groundbreaking study suggests that Homo sapiens, our own species, may have emerged at least half a million years earlier than previously thought. The analysis is based on a million-year-old human skull discovered in China.
Researchers posit that this finding also indicates a significantly longer period of co-existence between Homo sapiens and other hominin species, including Neanderthals, than previously understood.
According to the scientists, their analysis “totally changes” our understanding of human evolution. If validated, this discovery would necessitate a revision of a key chapter in our evolutionary history.
However, experts in the field, where debates surrounding human origins are common, acknowledge the plausibility of the study’s conclusions while emphasizing that they remain subject to further scrutiny.
The research, published in the prestigious journal Science, reportedly surprised the research team, which included academics from a Chinese university and the UK’s Natural History Museum.
“From the very beginning, when we got the result, we thought it was unbelievable. How could that be so deep into the past?” explained Prof Xijun Ni of Fudan University, who co-led the analysis.
“But we tested it again and again to test all the models, use all the methods, and we are now confident about the result, and we’re actually very excited.”
Upon initial discovery, the skull, designated Yunxian 2, was presumed to belong to Homo erectus, a more primitive ancestor known for being the first large-brained human species. This assumption was based on its age, approximately one million years, predating the previously accepted timeline for the emergence of more advanced human forms.
It was thought that Homo erectus eventually evolved and diverged around 600,000 years ago, leading to the emergence of Neanderthals and Homo sapiens.
However, the new analysis of Yunxian 2, which underwent peer review by independent experts, suggests that it does not belong to Homo erectus.
Instead, the skull is now believed to represent an early form of Homo longi, a sister species exhibiting a similar level of development to Neanderthals and Homo sapiens.
Genetic evidence suggests that these species co-existed. Therefore, if Yunxian 2 lived a million years ago, the researchers argue, early forms of Neanderthals and our own species likely existed during that period as well.
This compelling analysis significantly pushes back the timeline for the evolution of large-brained humans by at least half a million years, according to Prof Chris Stringer of the Natural History Museum, a co-lead on the research.
He suggests that million-year-old Homo sapiens fossils may already exist somewhere on the planet, awaiting discovery.
Determining the species and age of early human remains involves analyzing both skull morphology and genetic data. In the case of Yunxian 2, both methods were employed, leading to consistent conclusions.
However, other researchers, such as Dr Aylwyn Scally, an evolutionary geneticist at Cambridge University, point out the inherent uncertainties in both methodologies.
“One has to be particularly tentative about the the timing estimates, because those are very difficult to do, regardless of what evidence you’re looking at, be that genetic or fossil evidence,” he stated.
“Even with the largest amount of genetic data, it is very difficult to place a time when these populations may have coexisted to within 100,000 years, or or even more.”
He added that while Profs Ni and Stringer’s conclusions are plausible, they remain uncertain and require further supporting evidence.
“That picture is still quite unclear to us, so if the conclusions of this research are supported by other analyses, ideally from some genetic data, then I think we would start to be increasingly confident about it,” he told BBC News.
Given that the earliest known evidence of Homo sapiens in Africa dates back 300,000 years, it is tempting to speculate that our species may have initially evolved in Asia.
However, Prof Stringer cautions that there is insufficient evidence to draw definitive conclusions at this stage, as million-year-old human fossils from Africa and Europe also require integration into the analysis.
“There is some genetic evidence that points to the even earlier emergence of our species which may have recombined with our lineage, but this is not yet proven,” he told BBC News.
The revised timeline implies that these three human species co-existed for approximately 800,000 years, a considerably longer period than previously estimated, potentially interacting and interbreeding during that time.
The earlier emergence also offers a potential explanation for the numerous human fossil remains dating from 800,000 to 100,000 years ago that have been difficult for scientists to classify and place within the human family tree – often referred to as the “muddle in the middle”.
The revised timeline, with the earlier emergence of Homo sapiens, Homo longi, and Neanderthals, offers a potential resolution to this problem. According to Prof Ni, it allows for the categorization of these previously difficult-to-classify fossils as subgroups belonging to one of the “big three,” or their more primitive ancestors, such as Asian Homo erectus and heidelbergensis.
“Human evolution is like a tree,” he said. “This tree included several branches, and there were three major branches that are closely related, and they may have some interbreeding to each other, and they coexisted for almost 1 million years. So this is an unbelievable result.”
The skull was excavated along with two others from Hubei Province. However, these were damaged and crushed, contributing to the initial misclassification of Yunxian 2 as Homo erectus.
To restore the skulls to their original shape, Prof Ni’s team scanned them and used computer modeling techniques to correct distortions, subsequently creating 3D-printed replicas.
This reconstruction allowed the scientists to reclassify the skulls as belonging to a separate, more advanced group of humans.
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