Balihow – Groundbreaking research from the University of Cambridge is rewriting the story of human origins, suggesting that modern humans didn’t descend from a single ancestral group. Instead, we are the product of a “genetic reconciliation” between two ancient human populations that had been separated for over 1.5 million years.
For the past two decades, the prevailing scientific belief has been that Homo sapiens originated from a single lineage, evolving in Africa approximately 200,000–300,000 years ago. However, this new study, published in Nature Genetics, proposes a compelling alternative: roughly 300,000 years ago, two distinct ancient human populations, which had diverged for 1.5 million years, reconnected and genetically intermingled.
Intriguingly, the first population contributed approximately 80% of the DNA found in modern humans, while the second population contributed about 20%, notably influencing genes related to brain function and neural processing.
“The question of where we come from has preoccupied humanity for centuries,” said Dr. Trevor Cousins, lead author of the study from the Department of Genetics, University of Cambridge. “For a long time, we thought we evolved from a single, continuous lineage. But the precise details remained elusive.”
Significantly Larger Than Neanderthal DNA Contribution
It was previously understood that modern humans possess DNA from Neanderthals and Denisovans due to interbreeding around 50,000 years ago. However, this newly discovered genetic event is of a far greater magnitude.
Neanderthal DNA accounts for only about 2% in non-African humans. In contrast, this reconciliation event from 300,000 years ago contributes up to ten times more genetic material and is present in all human populations today.
“Certain genes from the minority population, especially those related to brain function, may have been particularly crucial in human evolution,” Cousins added.
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Utilizing Modern DNA, Not Fossils
Unlike traditional approaches that rely on DNA extracted from fossils, the research team analyzed DNA from modern humans. They leveraged data from the 1000 Genomes Project, a global initiative that sequenced the DNA of diverse populations across Africa, Asia, Europe, and the Americas.
The team developed a novel algorithm called ‘cobraa,’ which models how ancient human populations diverged and subsequently merged. The algorithm was rigorously tested on simulated data before being applied to real-world data.
“Soon after these two ancestral populations separated, we observed an extreme bottleneck in one of them—a drastic reduction in size before a slow recovery over a million years,” explained Prof. Aylwyn Scally. “This population ultimately contributed approximately 80% of modern human DNA and also appears to be the ancestor of Neanderthals and Denisovans.”
Interestingly, genes from the minority population were more prevalent in regions of the genome less involved in gene function, indicating a process of natural selection.
“It appears these genes were initially a poor fit within the majority genetic background, suggesting a process called purifying selection—where detrimental mutations are gradually eliminated by natural selection,” the researcher explained.
However, the genes from the minority group related to brain function and neural processing persisted, suggesting they conferred an evolutionary advantage.
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Broader Implications for Evolutionary Science
The ‘cobraa’ model isn’t limited to human studies; it was also applied to other species, including bats, dolphins, chimpanzees, and gorillas. The results consistently pointed to complex ancestral population structures, suggesting that evolution through branching and merging pathways may be a common pattern throughout the animal kingdom.
“It’s becoming increasingly clear that the idea of species evolving in a straight line without any mixing is overly simplistic,” Cousins stated. “Genetic exchange appears to be a vital part of the emergence of new species across the animal kingdom.”
Who Were These Mysterious Ancestors?
The identities of these two ancient groups remain a mystery. However, based on the fossil record, scientists speculate they could include Homo erectus, which inhabited Africa and Asia, and Homo heidelbergensis, which was also widely distributed during that period.
Researchers emphasize that more archaeological and genetic data are needed to precisely map these groups within the human family tree.
Scientists are hoping to refine the ‘cobraa’ model to capture gradual genetic exchange, rather than just abrupt separation and merging. They also aim to investigate how these findings relate to fossil discoveries of ancient humans, which reveal greater diversity in body shapes and cultures than previously thought.
“The fact that we can reconstruct events from hundreds of thousands to millions of years ago using only today’s DNA is truly remarkable,” Scally said. “It shows that our history is far richer and more complex than we ever imagined.”
Read also: When Did Modern Humans Homo Sapiens First Appear?
Ringkasan
New research suggests that modern humans originated from a genetic reconciliation between two ancient human populations that had been separated for over 1.5 million years, challenging the prevailing belief of a single ancestral lineage. This study indicates that roughly 300,000 years ago, these two distinct groups reconnected and genetically intermingled, with one population contributing approximately 80% of modern human DNA, and the other influencing genes related to brain function.
Researchers analyzed modern human DNA using a novel algorithm called ‘cobraa’ to model ancient population divergence and merging. The findings reveal a significantly larger genetic contribution from this ancient reconciliation event compared to Neanderthal DNA. Furthermore, the persistent genes from the minority population, particularly those related to brain function, suggest they conferred an evolutionary advantage, highlighting the complex and intertwined nature of human evolution.