Neanderthals were our closest extinct human relatives, and fragments of their DNA are present in many people today as a result of ancient interbreeding. These hominins, who diverged from our ancestors around 500,000 years ago, lived across Europe and Asia. This inherited genetic material is not merely a historical curiosity; it actively influences a variety of traits in modern humans. Understanding this genetic inheritance helps piece together the story of human migration and adaptation across the globe.
The Prehistoric Origin of Neanderthal DNA in Humans
The introduction of Neanderthal DNA into the modern human gene pool began when groups of Homo sapiens moved out of Africa. As these early modern humans expanded into Eurasia, they encountered Neanderthal populations that had been established there for hundreds of thousands of years. The primary period of this intermingling occurred roughly 47,000 years ago and may have lasted for nearly 7,000 years, likely centered in Western Asia.
The children of these unions carried DNA from both Homo sapiens and Neanderthals. As modern humans continued to spread across Europe and Asia, they carried these genetic fragments with them, embedding the Neanderthal legacy into the DNA of subsequent generations.
Detecting Ancient Genes in Modern Genomes
Identifying these ancient genetic fragments is a complex process. The foundation was laid by sequencing DNA from Neanderthal bones, an effort pioneered by researchers like Svante Pääbo. This work faced challenges, including DNA degradation and contamination from microbes. Scientists developed meticulous methods to isolate and piece together the short, fragmented strands of authentic Neanderthal DNA, resulting in a reference Neanderthal genome.
With this reference complete, computer algorithms scan the genomes of present-day humans, looking for stretches of DNA that match the Neanderthal sequence. A part of this process involves using the genomes of individuals of sub-Saharan African descent as a baseline. Genetic sequences found in non-Africans that match the Neanderthal genome but are absent in the African baseline are identified as having a Neanderthal origin.
Global Distribution and Percentage
The legacy of this ancient interbreeding is not evenly distributed. The amount of Neanderthal DNA in a person’s genome is linked to the migration patterns of their ancestors. Because the interbreeding events occurred in Eurasia after Homo sapiens had migrated out of Africa, Neanderthal DNA is found almost exclusively in people of non-African descent.
On average, individuals of European or Asian descent have between 1% and 2% Neanderthal DNA. Some studies suggest East Asians have a slightly higher percentage than Europeans. While this percentage seems small, it means that around 40% of the entire Neanderthal genome has survived in scattered fragments across the modern human population. More recent research has also detected trace amounts in some African populations, likely due to later migrations back into Africa.
The Functional Impact of Neanderthal Genes
The small percentage of Neanderthal DNA carried by many humans is not silent, influencing everything from our appearance to our susceptibility to certain diseases. The inherited DNA has been linked to both beneficial adaptations and negative health risks. Neanderthal genes related to the immune system likely provided an advantage against local pathogens in Europe and Asia. However, some of these same genes are associated with a heightened risk for allergies and autoimmune conditions like lupus and Crohn’s disease.
Traits related to skin and hair are also influenced by this inheritance. Certain Neanderthal variants affect keratin, a protein in skin and hair, and may have helped human skin adapt to different levels of UV radiation. Researchers have also linked specific Neanderthal alleles to an increased risk for:
- Type 2 diabetes
- Issues with blood clotting
- Nicotine addiction
- Depression
It is important to understand that these genes only create a predisposition; they do not guarantee that an individual will develop a particular condition.