When human ancestors ventured out of Africa over 50,000 years ago, they encountered Neanderthals who already shared some of their genes. Today, Homo sapiens are the only human species on Earth, but this wasn’t always the case. Around 400,000 years ago, while our ancestors were thriving in East Africa, Neanderthals were living in Eurasia. These two groups were separated by vast distances, considering that traveling by foot was the only option. Fast forward to 50,000 years ago, Homo sapiens arrived in Europe, and Neanderthals disappeared. Was it a coincidence, or did our ancestors play a role in their demise? This question has been debated for years.
Early Humans Left Africa Much Earlier Than Previously Thought https://t.co/rTZEgxqrsv
— Jan McVicker (@JanMcVicker) July 13, 2024
The Neanderthal genome was sequenced in 2010, revealing traces of their DNA in modern humans. This suggested that there was some form of contact, maybe even interbreeding, between these ancient humans. Interestingly, these bits of Neanderthal DNA in us have been linked to conditions like COVID-19 susceptibility, Type 2 diabetes, and autism.
Recent studies have flipped the narrative, investigating how many Homo sapiens genes were present in the Neanderthal genome. A new story emerged, suggesting that our ancestors made multiple journeys out of Africa, meeting and interbreeding with Neanderthals along the way.
In a recent study, Liming Li and colleagues analyzed 2,000 human genomes, along with three Neanderthal and one Denisovan genome. They looked at the flow of genetic information over a 200,000-year period. Surprisingly, they found that Neanderthal DNA contained 2.5-3.7 percent human ancestry, which is more than the 2 percent of Neanderthal DNA found in contemporary humans.
‘People w/ Neanderthal genes didn’t abruptly vanish—their offspring just acquired more & more modern human DNA. “They were overwhelmed by waves of modern humans extending out of Africa…The modern human population eventually absorbed the Neanderthals.”’https://t.co/AoaCcr6y9u
— Jessie Slater PhD (@subbasegirl) July 12, 2024
Their model suggested that two waves of gene flow from humans to Neanderthals occurred before the final encounter 50,000 years ago. The first wave happened around 250,000 to 200,000 years ago, and the second wave between 120,000 to 100,000 years ago. These timeframes align with the presence of a Nile-Sinai land bridge connecting Africa and Europe. During these events, Homo sapiens migrated to Europe, interbred with Neanderthals, and their mixed descendants integrated into Neanderthal populations.
When another wave of Homo sapiens met Neanderthals 50,000 years ago, the direction of gene flow reversed, with non-African humans assimilating Neanderthal ancestry. Whether Neanderthal-to-human gene flow in African humans happened exclusively after this final wave remains an open question. Future studies on African genetic diversity could reveal more migration patterns within Africa and possibly back to the continent.
Li and his team also found that accounting for the Homo sapiens component in the Neanderthal genome reduced the estimated Neanderthal population size by about 20 percent. This suggests that small population sizes led to more interbreeding and the accumulation of harmful mutations, which were then inherited by Homo sapiens.
On July 10, 1997, scientists in London reported DNA analysis findings from a Neanderthal skeleton. These findings supported the “out of Africa” theory, suggesting that modern humans originated in Africa and migrated, interbreeding with Neanderthals. pic.twitter.com/ckeI7Zdrij
— Alex’s Daily History (@alex451g) July 10, 2024
Joshua Akey, a senior author on the study, stated that Neanderthals were likely on the brink of extinction for a long time. The repeated encounters with Homo sapiens over 200,000 years acted like relentless waves eroding a beach, gradually leading to the Neanderthals’ assimilation into the larger Homo sapiens population.
The study, which provides new insights into these ancient interactions, is published in Science.
Key Points:
- Ancient Interactions: Human ancestors met Neanderthals multiple times over 200,000 years, leading to significant gene flow.
- Gene Sequencing: Modern humans have Neanderthal DNA, and recent studies show Neanderthals also had human genes.
- Two Major Waves: Significant gene exchanges occurred around 250,000-200,000 years ago and 120,000-100,000 years ago.
- Population Impact: Neanderthal populations were small and interbreeding with humans contributed to their decline.
- Study Findings: The research published in Science highlights the complex genetic history and interactions between ancient humans and Neanderthals.
TL Holcomb – Reprinted with permission of Whatfinger News
