The term “modern neanderthal” is a colloquialism describing contemporary humans who carry a small but significant amount of DNA from our extinct relatives. Neanderthals vanished as a distinct group around 40,000 years ago, but their genetic legacy persists within our own cells, a faint echo from the deep past.
This inheritance is not uniform, but it is widespread among people outside of Africa. The fragments of Neanderthal DNA in our genomes are active pieces of genetic code that influence a variety of traits in present-day humans. Understanding this ancient genetic footprint offers a window into our biology and evolutionary journey.
The Genetic Echo of Interbreeding
The introduction of Neanderthal DNA into the Homo sapiens gene pool resulted from our expansion across the globe. As modern human populations migrated out of Africa, they moved into territories in Eurasia that were already inhabited. For hundreds of thousands of years, Neanderthals had lived and adapted to the climates of Europe and Western Asia.
Beginning around 50,000 to 60,000 years ago, migrating modern humans encountered and interacted with established Neanderthal populations. These encounters led to periods of interbreeding where the two groups mixed. Genetic analysis of ancient human remains confirms this mixing occurred, leaving a durable mark on the human genome.
This gene flow happened over an extended period, perhaps as long as 7,000 years, in various locations across Eurasia. The primary interbreeding events took place before humans had diversified widely across the continent, which explains why the genetic signature is found broadly across Eurasian peoples. Eventually, around 40,000 years ago, Neanderthals disappeared from the fossil record, but not before their genetic contribution was passed on.
Identifying Neanderthal DNA in Humans
The legacy of ancient interbreeding is not evenly distributed among modern human populations. On average, individuals of European and Asian descent carry between 1% and 2% Neanderthal DNA. This is because the interbreeding events occurred in Eurasia after modern humans had left Africa, localizing the genetic exchange to those continents.
People of sub-Saharan African ancestry have virtually no Neanderthal DNA because their ancestors did not inhabit the regions where Neanderthals lived. This geographic distinction is a tool for scientists studying human migration. By comparing modern genomes with the Neanderthal genome, researchers can pinpoint the exact sequences that were passed down.
Identifying this ancient DNA is a recent scientific achievement, pioneered by researchers like Nobel laureate Svante Pääbo. By developing new techniques to extract and sequence highly degraded DNA from ancient bones, his team successfully reconstructed the Neanderthal genome. This breakthrough allows scientists and commercial DNA services to scan a person’s DNA for specific Neanderthal genetic markers.
Traits Inherited from Neanderthals
The small percentage of Neanderthal DNA in modern people has a noticeable impact on a range of biological traits, especially the immune system. Modern humans inherited several genes from Neanderthals that are part of the innate immune system, the body’s first line of defense. Specifically, variants in a family of genes called Toll-like receptors (TLR1, TLR6, and TLR10) were passed down.
This genetic transfer bolstered the immune systems of modern humans moving into new environments with unfamiliar pathogens, providing a survival advantage against local diseases. This ancient inheritance means that for many people today, a part of their ability to fight infection comes from their Neanderthal ancestors.
Physical characteristics related to skin and hair are also linked to Neanderthal DNA. Genes that influence the production of keratin, the protein in our skin, hair, and nails, show high levels of Neanderthal ancestry. For example, Neanderthal variants in genes like KRT71 are common in Europeans and Asians and affect traits such as hair straightness and texture.
Other genes, such as BNC2, are tied to skin pigmentation and an individual’s tendency to tan or burn. Neanderthal versions of this gene are associated with both lighter skin and increased sun sensitivity, contributing to the diversity of skin tones in modern Eurasians. It is a common misconception that red hair is a Neanderthal trait, as the specific mutations for it in modern humans have not been found in Neanderthal genomes.
Beyond appearance, Neanderthal genes can influence metabolism and the risk of certain diseases. This ancient DNA is linked to several modern health factors:
- An increased rate of blood clotting.
- Changes in how the body metabolizes fats.
- A higher risk for modern health conditions, including type 2 diabetes and autoimmune diseases like lupus and Crohn’s disease.
- A major genetic risk factor for severe COVID-19 that was inherited from Neanderthals.
Evolutionary Advantages and Disadvantages
The persistence of Neanderthal DNA in the modern human gene pool demonstrates adaptive introgression, the process of gaining beneficial genetic material from another species. For modern humans expanding into Eurasia, these borrowed genes offered a shortcut to adaptation. Acquiring pre-adapted genes was much faster than waiting for new mutations to arise and spread.
The advantages in the past were clear. A more aggressive immune response helped fend off local infections. Genes that promoted faster blood clotting were beneficial for surviving injuries from hunting or other daily hazards. Similarly, changes in skin pigmentation may have helped optimize vitamin D production in regions with less sunlight.
This ancient inheritance has led to an “evolutionary mismatch” in the modern world. Traits that were once advantageous can have neutral or negative consequences in current lifestyles. For instance, an immune system calibrated for constant pathogenic threats can become over-reactive in our sterile environments, contributing to allergies and autoimmune disorders.
The genetic tendency for rapid blood clotting, once a lifesaver, now increases the risk for strokes and deep vein thrombosis in more sedentary populations. Likewise, variants that influenced fat storage in a world of food scarcity might now predispose individuals to obesity and type 2 diabetes. These Neanderthal genes are not inherently “good” or “bad”; their effects are dependent on the environmental context.