How Did Homo sapiens’ Mating With Neanderthals, Denisovans, and Other Hominins Over 50,000 Years Ago Alter Human History? — Here’s What Scholars Found

Around 50,000 years ago, there were many different kinds of hominins that lived in various environments on Earth together with the modern human species. Our ancestors are thought to have originated and evolved in Africa. Then, 70,000 to 50,000 years ago, they migrated out to different continents, beginning with Europe and Asia.

In these new places, they encountered other human species already living and established in the area, like the Neanderthals and Denisovans. Then, when these groups met, they didn’t just compete with one another. Evidence suggests that they also interbred and produced offspring together. This mixing is still found in the DNA of humans today, but how exactly did these events change our history? Could it have a larger effect than we realize? Let’s find out more in this article.

Genetic Legacies Passed Down

When humans met and interbred with different other hominins, they didn’t just produce children; their genes also survived and were passed on to the modern human population. Studies suggest that most individuals outside of Africa have about 1 to 4% of their DNA coming from Neanderthals. While Denisovans contributed up to 5% of the genes in humans in regions like Tibet, South East Asia, and Oceania.

This process is often referred to as introgression, where a different species successfully inserts its genome into another. It happened when two different hominins created an offspring together, and that individual grew up and mated with another of the parental species. Over time, these ancient genes will be incorporated into the gene pool of the other until it is passed down to most of the population.

Read more: Smithsonian Human Origins

Adaptation to New Environments

Did Homo Sapiens Really Mate With Neanderthals?

So, if hominins like Neanderthals and Denisovans passed on some of their DNA to us, how could this simple bit of genome affect human history? Today, it still has some noticeable influence on some of our traits and characteristics, like Neanderthal DNA appearing in modern humans in key regions affecting their hair, skin, and immunity.

But the majority of changes could only be observed genetically or are very subtle, such as the case with Denisovan DNA. However, their real benefits were mostly felt by our ancestors. When they migrated out of Africa around 70,000 to 50,000 years ago, they needed to adapt to new lands and environments. But these other hominins have already done that, and are well-adapted to their current natural habitats.

By interbreeding with them, Homo sapiens could have inherited some helpful traits that would have eventually contributed to their survival. For example, Denisovans have traits that allowed them to better adapt to colder high altitude places and prevent sickness from it. In modern day, Tibetans have inherited these characteristics, allowing them to live in harsh places like the Tibetan Plateau.

Health, Disease, and Complex Consequences

Interbreeding not only passed down genes that could be helpful and advantageous, but it also could result in the inheritance of negative and disadvantageous genes. For example, some archaic genomes could make the human population more vulnerable to certain diseases and negatively affect their immune system responses.

They could have also passed down traits that may be beneficial to their own original habitats, but when other humans migrated to new environments, these very same traits could have become disadvantageous. Moreover, the majority of the genes that were passed down most likely did not survive through the years either, because of natural selection and continuous adaptations of humans.

Instead, the pattern of which genes survive and which ones don’t was probably based on how advantageous, disadvantageous, or neutral they are. Thus, the point is that interbreeding with other hominins changed the modern human species in a very complex way, where some genes that were passed to us were positive, some were negative, and a few were neutral.

Read more: PubMed Central

Culture, Identity, and the Human Story

Tales of Human History Told by Neandertal and Denisovan DNA That Persist in Modern Humans

But beyond just the genes, the interbreeding of different human species also could have meant that they mixed culture and identities too. The two groups, instead of just competing with each other, may have formed a helpful relationship that could have included an exchange of knowledge, skills, and technologies.

Additionally, some people think that the path of the modern human species’ evolution was direct and simple, where we just replaced and outcompeted all the other hominins in different areas of the world. But the reality is more complex, because some of them became part of us, whether it is through interbreeding or their species was absorbed into ours.

Today, the human population still carries DNA from different hominins. Some are known because their fossils have been found, like Neanderthals and Denisovans, but there are also some archaic ghost species we have never found physical evidence of that could have mated with Homo sapiens. The only clue of their existence was found in some human group’s DNA. These known and unknown hominins helped form our genetic lineage, and they will forever be a part of the human story.

Author's Final Thoughts

Homo Sapiens mating with Neanderthals, Denisovans, and other hominins around 50,000 years ago changed human history, because there could have been a world where we did not survive without their help and their genes. These interbreeding and exchanges of DNA, culture, and knowledge helped us adapt to new lands, influenced our health, and changed how we perceived the human lineage.

Their ancient interactions are a reminder that evolution is not a straight path with a goal in mind, but instead it is a complex interplay of many different factors and species. So, today, every time you look at yourself and other people, remember that they are not just a product of the current modern human species but instead shaped by the many branches and ancestors of the human family tree.

Read next: Why Did the Human Population Explode After the Advent of Farming Around 10,000 Years Ago? — Here’s What Experts Believe

References & Further Reading

Green, R. E., et al. (2010). A draft sequence of the Neandertal genome. Science. https://doi.org/10.1126/science.1188021

Meyer, M., et al. (2012). A high-coverage genome sequence from an archaic Denisovan individual. Science. https://doi.org/10.1126/science.1224344

Huerta-Sánchez, E., et al. (2014). Altitude adaptation in Tibetans caused by introgression of Denisovan-like DNA. Nature. https://www.nature.com/articles/nature13408

Simonti, C. N., et al. (2016). The phenotypic legacy of admixture between modern humans and Neandertals. Science. https://doi.org/10.1126/science.aad2149

Dannemann, M., & Kelso, J. (2017). The contribution of Neanderthals to phenotypic variation in modern humans. American Journal of Human Genetics. https://pmc.ncbi.nlm.nih.gov/articles/PMC5630192/

Zeberg, H., & Pääbo, S. (2020). The major genetic risk factor for severe COVID-19 is inherited from Neanderthals. Nature. https://www.nature.com/articles/s41586-020-2818-3

Zeberg, H., & Pääbo, S. (2021). A genomic region associated with protection against severe COVID-19 is inherited from Neandertals. Proceedings of the National Academy of Sciences. https://www.pnas.org/doi/10.1073/pnas.2026309118

Browning, S. R., et al. (2018). Analysis of human sequence data reveals two pulses of archaic Denisovan admixture. Cell. https://www.cell.com/fulltext/S0092-8674(18)30175-2