Scientists have discovered a surprising link between ancient Homo sapiens and Neanderthals. By studying the Y chromosome and mitochondrial DNA of Neanderthals, researchers found that these genetic components were more similar to those of modern humans than expected. This suggests that there was a significant amount of gene flow between the two species, likely due to interbreeding.
The researchers propose that this gene flow occurred tens to hundreds of thousands of years ago, long before the well-known migration of Homo sapiens out of Africa around 80,000 years ago. This early gene flow may have been driven by the introduction of human DNA into the Neanderthal gene pool, which provided a fitness advantage due to the larger population size of humans.
The discovery of this ancient gene flow has significant implications for our understanding of human evolution and the relationship between humans and Neanderthals. It suggests that the Out of Africa migration was just one of several waves of human dispersals into Eurasia, and that humans and Neanderthals had a more complex and ancient relationship than previously thought.
Here are the extracted facts:
1. In 2020, researchers studying Neanderthal genomes found a surprising similarity between Neanderthal and Homo sapiens Y chromosomes.
2. The researchers developed a new method to extract Y chromosome fragments from less well-preserved Neanderthal remains.
3. The Y chromosomes of three male Neanderthals were found to be much more similar to Homo sapiens than expected.
4. The Y chromosomes of Neanderthals were replaced with Homo sapiens-like Y chromosomes.
5. Scientists agree that a group of Homo sapiens from Africa migrated into Eurasia around 80,000 years ago and interbred with Neanderthals.
6. The Y chromosome replacement in Neanderthals likely occurred before the migration out of Africa around 80,000 years ago.
7. The replacement of the Y chromosome in Neanderthals is estimated to have occurred tens or hundreds of thousands of years before the migration out of Africa.
8. Neanderthals and Denisovans were each other's closest evolutionary relatives.
9. Mitochondrial DNA is a separate genome that is passed down only from the mother.
10. The oldest Neanderthal mitochondrial genomes come from fossils found in Spain dating to around 430,000 years ago.
11. The mitochondrial DNA of later Neanderthals was replaced with DNA that is more human-like.
12. A previously unknown period of early gene flow between ancient Homo sapiens and Neanderthals is proposed to have occurred between 470,000 and 220,000 years ago.
13. A wave of ancient Homo sapiens from Africa or a group closely related to them migrated into Eurasia during this period.
14. The wave of ancient Homo sapiens eventually died out without leaving direct descendants in modern populations.
15. The genetic legacy of this wave of ancient Homo sapiens was left in Neanderthals through interbreeding.
16. At least one female individual from the wave of ancient Homo sapiens reproduced with a male Neanderthal, and their hybrid offspring inherited her mitochondrial DNA.
17. The hybrid offspring were absorbed into Neanderthal populations and went on to reproduce with other Neanderthals.
18. The mitochondrial DNA of the hybrids eventually replaced the original Neanderthal mitochondrial DNA over tens to hundreds of thousands of years.
19. The human-like Y chromosome and mitochondrial DNA in Neanderthals may have provided fitness advantages over their Neanderthal versions.
20. The advantages may have been due to the smaller population size of Neanderthals, which made them more susceptible to harmful mutations.
21. Natural selection favored the human versions of the Y chromosome and mitochondrial DNA, leading to their rapid spread through the Neanderthal gene pool.
22. The Denisovans lived much further away from Homo sapiens than Neanderthals and had less gene flow with them during early waves of migration.
23. The Out of Africa migration around 80,000 years ago was likely one of several waves of ancient human dispersals into Eurasia.
24. The encounters between humans and Neanderthals may have stretched back tens to hundreds of thousands of years.
25. The introduction of human DNA into the Neanderthal gene pool long ago may have changed them forever.