Here is a concise summary of the text:
**Title:** Ancient Human-Neanderthal Interbreeding Revealed through DNA
**Key Findings:**
1. **Neanderthal Y-Chromosome Surprise**: Scientists found that Neanderthals' Y-chromosomes are more similar to those of modern humans (Homo sapiens) than expected, suggesting a human-like Y-chromosome replaced the original Neanderthal one.
2. **Early Interbreeding**: This replacement likely occurred due to an early, previously unknown period of gene flow between ancient Homo sapiens and Neanderthals, dating back tens to hundreds of thousands of years before the well-known 80,000-year-old migration out of Africa.
3. **Mitochondrial DNA Parallels**: Similar replacement patterns were found in Neanderthal mitochondrial DNA, which also became more human-like over time, supporting the early interbreeding theory.
4. **Fitness Advantages**: The human DNA may have provided a selective advantage due to the smaller population size of Neanderthals, which led to a higher accumulation of harmful mutations in their original DNA.
**Implications:**
* A more complex and ancient relationship between humans and Neanderthals than previously thought
* Multiple waves of ancient human dispersals into Eurasia, with the 80,000-year-old migration being just one of them
* Neanderthals had already been genetically influenced by humans before the well-known migration event.
Here are the key facts extracted from the text, each numbered and in short sentences:
**Facts about the Announcement and Other Topics**
1. A puzzle was released, featuring the reconstruction of Platykotta, considered the oldest false crab.
2. A 2023 calendar featuring "main characters of paleontology" is available at ComplexlyCalendars.com.
**Facts about Neanderthals and Genetics**
3. In 2020, scientists successfully sequenced the Neanderthal Y-chromosome using a new method.
4. The Neanderthal Y-chromosome is more similar to that of Homo sapiens than expected.
5. The Y-chromosome replacement in Neanderthals is believed to have occurred tens to hundreds of thousands of years before the known migration out of Africa (around 80,000 years ago).
6. Neanderthals and Denisovans were each other's closest evolutionary relatives.
7. Only a small percentage of Neanderthal DNA can be traced back to interbreeding with Homo sapiens.
**Facts about Mitochondrial DNA and Interbreeding**
8. Neanderthal mitochondrial DNA shows a puzzling link with ancient Homo sapiens.
9. The oldest Neanderthal mitochondrial genomes (from fossils in Spain, ~430,000 years ago) are Denisovan-like.
10. Later Neanderthal mitochondrial DNA was replaced with human-like DNA, suggesting early interbreeding.
11. A proposed period of very early gene flow between ancient Homo sapiens and Neanderthals occurred between 470,000 and 220,000 years ago.
**Facts about Population Dynamics and Natural Selection**
12. Small population sizes (like those of Neanderthals) lead to a faster buildup of harmful mutations.
13. Ancient human DNA introduced into Neanderthal populations was favored by natural selection and rapidly spread.
14. Denisovans, living farther away, had less gene flow with ancient Homo sapiens, explaining the lack of similar replacements in their gene pool.
**Facts about Human Migration and Evolutionary History**
15. The "out of Africa" migration around 80,000 years ago was likely one of several waves of ancient human dispersals into Eurasia.
16. Encounters between humans and Neanderthals stretch back tens to hundreds of thousands of years, prior to the successful migration around 80,000 years ago.