8 Neanderthal Traits in Modern Humans
Neanderthal Genes Influencing Human Traits
No one knows precisely why Neanderthals died out 40,000 years ago, but we do know there was some intermarriage between their community and our ancestors. Many of these genes have been purged from the modern human population over time due to natural selection, so the current prevalence is only 1-4% of the current human genome. While the prevalence of genes from Neanderthals are rare in humans (<2% in non-African populations), these genes still contribute to different physical characteristics. The inherited traits from the Neanderthal population sometimes offer benefit, and sometimes are linked to disease causing traits. The vast majority of the identified genes remaining in the non-African population are associated with hair and skin color. Genes with a Neanderthal origin are called archaic genes.
When humans and Neanderthals coexisted, up to 10% of the human genome was comprised of Neanderthal genes.
A common question arising from the intermarriage of humans and Neanderthals is the question of fertility among the offspring of these unions. The evidence (Sankararaman, S. et. al., 2016) indicates that the hybrid children were less fertile, as the prevalence of Neanderthal genes on the X chromosome are fewer than those found on the autosomal (non-sex) chromosomes. This finding is due to natural selection, which suggests the Neanderthal genes on this chromosome impaired fertility and have reduced over time as the X chromosomes with more human genes produced more fertile males.
In general, genes which conferred benefit to the human population remained, and genes which caused harm were eliminated over the course of time.
Neanderthal Range in Europe and Asia
How Do We Know Which Genes Come from Neanderthals?
The genomes of several Neanderthals have been fully sequenced, allowing for researchers to compare the genomes of modern day humans alongside the archaic genes. In addition, researchers compare the genomes of people from sub-Saharan Africa, which contain absolutely no archaic genes as this population never existed in Africa. Since human population migrated out of Africa, once hybridization occurred the population spread outward to Europe and Asia. Human populations in Europe, Asia, and Oceana contain the highest percentage of archaic genes (though this is still a small percentage).
Alleles are variant forms of a gene that are found on the same location on a chromosome.
By comparing the genomes which contain no traces of Neanderthal genes, the fully sequenced archaic genomes, and the genetics of modern day Europeans , scientists are able to piece together which genes are derived from a Neanderthal ancestor.
Selected Genetic Alterations from Archaic Genes
Genes Affected by Neanderthal Alleles
Tendency to have blood clots (DVT)
Delayed Sleep Period
Did Red Hair Come from Neanderthals?
A common urban myth states that red hair in humans comes from Neanderthals. Humans in today’s world generally have mutations on the melanocortin (MC1R) gene that cause an over-production of pheomelanin, which produces a red hair color. A second theory is that a separate gene that reduces the functionality of the MC1R gene is from Neanderthals (p.Arg307Gly), but none of these mutations have been observed in the fully sequenced genomes from two Neanderthals. In short, those with ginger hair in today’s world do not appear to have inherited the trait from Neanderthals.
1. Hair Color and Type
Several overlapping genes for both the human and Neanderthal population are linked to both blonde and dark hair. It appears that Neanderthals were as varied in skin tone and hair tone as modern day humans and it is impossible to identify the presence of an archaic genome by observing a current human’s hair or skin color. The formation of hair, which largely involves the production of keratin, is influenced by archaic genes. Two primary conditions remain in humans from our Neanderthal ancestors:
- Actinic Keratosis is caused by damage from exposure to ultraviolet light. This is a pre-cancerous condition and causes scaly bumps on a person’s skin surface. If left untreated, this skin lesion may develop into Squamous Cell Carcinoma.
- Seborrheic Keratosis are completely harmless skin growths that can range in color from tan to black. These growths are sometimes referred to as “barnacles.”
2. Immune System Benefits
Over 31 genes involved with the immune system in modern day humans are derived from an archaic ancestry. The continued existence of these genes indicates they are beneficial and protective against different forms of infection. Specific mutations that help defeat viral infections are present in both populations. The OAS1, OAS2, and OAS3 genetic changes inherited from the Neanderthals increase the activity of the anti-viral genes, which helps humans overcome contagious diseases.
Another inherited genetic mutation is called the TLR1/6/10 haplotype. This variation is found in the highest concentration in East Asia, and confers resistance to H. pylori and stomach ulcers. People who have this variant may also be more prone to allergies.
3. The “Night Owl” Sleeping Pattern
Genetic variants on ASB1 and EXOC6 are archaic genes that are associated with a preference for staying up late and napping during the daytime hours. The concentration of these genes increases in direct correlation to distance from the equator. The northern latitudes experience a greater shift in the day length, which affects circadian rhythm. The ASB1 and EXOC6 variants may confer a benefit to those who live in northern climates with short day-length cycles in the winter.
4. A Tendency for Depression from Archaic Genes
The same genetic inheritance regarding circadian rhythms is also associated with an increased level of chronic depression. Lack of sunlight is a known cause of depression among humans living in northern latitudes, and the prevalence of some of the mutations increases the farther a population is from the equator. Neanderthal alleles near the CDH6 gene are associated with an increased frequency of feeling unenthused and apathetic.
Addiction to substances such as tobacco is also influenced by these genes. While prevalent in less than 0.5% of the European population, one variant on the SLC6A11 gene increases the likelihood for addiction and is a positive predictor of smoking behavior.
5. Blood Clotting Issues and Deep Vein Thrombosis
In the European population, approximately 6.5% of people have a mutation on the SELP gene that increases a tendency to form blood clots. This gene is responsible for a protein that adheres cells and platelets to wound areas and to inflamed blood vessels.
Another archaic variant is for a gene encoding the Factor V protein. This mutation is separate from the most common genetic cause of blood clots in Europeans (Factor V Leiden). Those who have the rs3917862 allele have an increased rate of having thrombosis. When a person has both the Factor V Leiden mutation and the Neanderthal derived mutation, the risk of having a deep vein thrombosis is increased to a higher level than observed with the Factor V Leiden mutation alone.
6. Protein-Calorie Malnutrition
Neanderthals age a diet high in protein and low in carbohydrates. Thiamine is a nutrient primarily found in beef, liver, eggs, and other protein-rich foods. One archaic allele on SLC35F3 produces a thiamine transporting protein. This activity of the transporting protein was reduced in Neanderthals, who ate a diet highly rich in the nutrient. The presence of the archaic mutation can increase the chance of malnutrition, as the amount of thiamine (vitamin B1) available to the body is reduced for those who consume a diet high in refined carbohydrates. Unfortunately, since modern refinement practices reduce the amount of thiamine available in grains to begin with, humans with this mutation may be at a risk of this deficiency, also known as “beriberi.” This condition is known as “high calorie malnutrition,” as the person is obtaining enough calories, but is not getting enough of a particular nutrient for body functions to work correctly. Thiamine Deficiency can cause dysautonomia, including Postural Orthostatic Tachycardia Syndrome, or POTS. Other disorders including psychiatric disorders, swelling of the legs, vomiting, and heart failure can be caused by a vitamin B1 deficiency.
7. Eye Color
The OCA2 gene is responsible for producing hair, skin, and eye color. While people originating from Africa have over 74 genetic differences from the Neanderthal sequence for this gene, those from non-African locations only demonstrate a little over 10 differences from the archaic genome. This indicates a rather recent influx of Neanderthal genes into the human population that migrated out of Africa. One mutation that is consistent between the Neanderthals and modern-day humans is a mutation on OCA2 that produces a blue eye color. The origin of blue eye color, however, does not arise solely due to the presence of archaic genes. Modern-day humans also have mutations causing a blue eye color that are not present in the Neanderthals, so the origin of blue eyes is likely due to a multitude of factors.
8. Both Light and Dark Skin Inherited from Neanderthals
Both light and dark skin tones are observed in inheritance from the Neanderthal population. This indicates that this group had variation in skin tone, similar to modern humans.
Some alleles on the BNC2 gene are archaic and are derived from the Neanderthal population. This genetic variation causes an increased susceptibility to sunburn and is present in up to 66% of the European population. In addition to increasing the risk for sunburn, this variant causes skin lesions due to keratosis. This gene is responsible for a lighter skin tone and increased ability to process Vitamin D in low-sunlight conditions. These genetic mutations also cause an increase in susceptibility to skin cancer.
Interestingly, a smaller proportion of Europeans inherited darker skin from the Neanderthals. A gene located close to the BNC2 gene is associated with increased pigmentation in the skin. Up to 19% of the identified overlapping human-Neanderthal genes are associated with this second allele that produces darker skin.
Dannemann, M. & Kelso, J. (2017). The Contribution of Neanderthals to Phenotypic Variation in Modern Humans. The American Journal of Human Genetics, Volume 101, pp. 578-579.
Harris, K. & Neislen, R. (2016). The Genetic Cost of Neanderthal Introgression. Genetics, Volume 203, pp. 881-891.
Sankararaman, S., Swapan, M., Patterson, N., & Reich, D. (2016). The Combined Landscape of Denisovan and Neanderthal Ancestry in Present-Day Humans. Current Biology, Volume 26, pp. 1241-1247.
Gittelman, R., Schraiber, J., Vernot, B., Mikacenic, C., Wurfel, M., Akey, J. (2016). Archaic Hominem Admixture Facilitated Adaptation of Out-of-Africa Environments. Current Biology, Volume 26, pp. 3375-3382.
Simonti, C. et. al. (2014). The Phenotypic Legacy of Admixture Between Modern Humans and Neandertals. Science, Volume 343, pp. 737-741.
Questions & Answers
Do blue eyes come from neanderthals?
Blue eyes do not come from Neanderthals, and current data shows that Neanderthals had a variety of skin tones and had different eye colors (including brown). Two female Neanderthals from Croatia were studied and their genome demonstrated a likelihood that they had tawny skin, brown eyes, and brunette hair.
© 2018 Leah Lefler