Neanderthal DNA is a type of introgressed DNA, meaning it was transferred into the modern human gene pool through interbreeding with an archaic human species, Homo neanderthalensis. This genetic material represents a small but significant fraction of your genome, an echo of a time when two distinct human groups lived side-by-side.
The Science of Shared DNA
The mixing of modern human and Neanderthal DNA occurred shortly after Homo sapiens began migrating out of Africa approximately 60,000 to 70,000 years ago. This genetic exchange, known as introgression, is estimated to have taken place primarily in Western Asia, where the first populations encountered Neanderthals who had already inhabited Eurasia for hundreds of thousands of years. The most likely period for this interbreeding is estimated to be between 47,000 and 65,000 years ago.
Populations whose ancestors remained exclusively in sub-Saharan Africa generally carry negligible amounts of Neanderthal DNA. This is because the initial interbreeding happened after the ancestors of non-African populations had separated and moved into Eurasia. The Neanderthal genetic fragments that persisted in the modern human genome often offered an immediate survival advantage. These beneficial genes helped early Homo sapiens adapt rapidly to the novel climates, diets, and pathogens found in non-African environments.
Practical Methods for Discovery
The most accessible method for determining your Neanderthal ancestry is through commercial direct-to-consumer genetic testing companies. These services use genotyping arrays to analyze your DNA, looking specifically for single nucleotide polymorphisms (SNPs) that have been identified as originating from Neanderthals. The process involves collecting a saliva sample. The company extracts your DNA and compares thousands of your specific genetic markers to reference sequences derived from sequenced Neanderthal fossils.
The results are processed using specialized algorithms that calculate the likelihood that certain segments of your chromosomes match known Neanderthal DNA fragments. Companies like 23andMe and others that offer this analysis provide a report detailing your estimated Neanderthal ancestry. These tests do not sequence your entire genome, but instead look at a sample of markers, providing an estimate based on comparison to databases and scientific reference populations. The precision of the result is dependent on the quality of the reference Neanderthal genomes and the specific markers the company chooses to analyze.
Decoding Your Neanderthal Score
The resulting numerical value you receive from a genetic test is reported as a percentage of your total genome. For people of non-African descent, this percentage usually falls within a range of 1% to 4%. This value represents the proportion of your personal DNA that matches known Neanderthal sequences, not the percentage of Neanderthal DNA in the global human population.
Some reports also provide a “locus count,” which is the number of specific Neanderthal-derived genetic variants, or fragments, detected in your DNA. A common score for non-African individuals ranges from about 250 to 400 such variants. Crucially, having a higher percentage or fragment count does not make you “more Neanderthal,” as the small percentage is distributed across different parts of the genome. The location and function of the specific fragments inherited are far more significant than the total calculated amount.
Common Traits Linked to Neanderthal DNA
Many of the Neanderthal gene variants that survived natural selection are associated with traits related to the skin, hair, and immune system, reflecting adaptation to Eurasian environments. Certain Neanderthal gene fragments are linked to variations in skin and hair color, including lighter skin tones, and the propensity for straighter, thicker hair texture. These genes were likely advantageous in northern latitudes, where they could have aided in vitamin D production under reduced sunlight.
Neanderthal DNA also significantly influenced the modern human immune system, with some variants improving the ability to recognize and fight new pathogens encountered outside of Africa. However, this adaptation comes with trade-offs, as other Neanderthal variants are associated with an increased risk for autoimmune disorders such as lupus and Crohn’s disease. Inherited variants also affect behavior and physiology, including a tendency to be a “morning person” and a genetic link to increased nicotine addiction risk. Another functional trait is a variant that increases blood coagulation, which could have helped wounds heal faster in ancient times but may increase the risk of blood clots today.