This is a topic that I've been curious about for a long time, especially after taking an evolutions online course from Emory University where I learned about the emergence of humans' effects on the Neanderthals (spoiler alert: it didn't go too well for the Neanderthals). If you've ever tested your DNA using 23andMe or Geno 2.0, you've probably noticed that there's a little Neanderthal in you too! So, which human populations have more Neanderthal DNA than others, what is the cause of this, and does this have any effect on modern humans? Let's find out.
While many humans today have a miniscule percent of Neanderthal DNA due to prehistoric (remember the Neanderthals became extinct about 40,000 years ago) sexual encounters between our ancestors and Neanderthals, some populations have higher concentrations in their genome.
According to my research from this week, humans have inherited 1-4% of their DNA from Neanderthals. East Asians have the greatest amount of Neanderthal DNA (generally ~2.3-2.6%), Western Europeans have a little less (generally ~1.8-2.4%), and Africans have 0.3% (due to other human populations who interbred with Neanderthals and migrated back to Africa). This puzzled scientists because Neanderthal remains were not found east of the Altai Mountains in Central Asia, and yet various were found throughout Europe and the Middle East.
The answer to this lies in the idea that the distribution of Neanderthal DNA changed over time. When samples older than 20,000 years were tested in this study, published in the Science Advances journal for anyone interested in reading more, the genomes of Stone Age Homo sapiens in Europe had slightly more Neanderthal DNA than those in Asia. Although there was not enough data to reveal how this transition occurred in Asia, scientists suggested that the present pattern of Asian populations having more Neanderthal DNA than European populations developed later on. They suggested that it may have happened during the Neolithic transition when the practices of hunting and gathering were replaced with farming.
So, does having Neanderthal DNA really have an impact on humans today? Partially. In modern humans, Neanderthal DNA has a subtle, but significant impact on their biology.
Having Neanderthal DNA tends to be associated with diseases including diabetes, lupus, and Crohn's disease. According to a study done at Vanderbilt University in 2016 using a database containing 28,000 patients, associations were made between Neanderthal DNA and many traits including immunological, dermatological, neurological, psychiatric, and reproductive diseases.
While some Neanderthal variants may have been protective in ancient times, now they can actually be harmful in modern environments. For example, today Neanderthal variants can influence the risk for a skin disease called actinic keratosis which occurs as one ages and gets lots of sun exposure. This is because Neanderthal DNA has been proposed to affect cells called keratinocytes which help protect skin from environmental damage (ex. ultraviolet radiation & pathogens), and actinic keratosis is caused by abnormal keratinocytes. Another example is hypercoaguability (this is a fancy word for when one's blood clots more quickly) which may have been helpful in fighting pathogens and healing wounds in ancient times, by sealing wounds more quickly and preventing pathogens from entering the body, but now leads to strokes, pulmonary embolisms, and pregnancy complications.
Some psychiatric associations found were that a specific bit of Neanderthal DNA significantly increases the risk for nicotine addiction, and if overall Neanderthal variants are assessed it is easier to predict one's risk for depression.
Neanderthal variants can even affect how fast someone burns calories, hair color, height, sleeping patterns, mood, menopause age, bone density, and much more. In fact, 47 distinct traits in modern humans are influenced by Neanderthal DNA.
This pattern of associations that current populations retain today may have provided adaptative advantages to modern humans migrating out of Africa ~40,000 years ago.
Overall, it seems that Neanderthals, our closest ancient human relatives along with the Denisovans, are still very much present in practically all of us!
I had lots of fun researching this topic, comment or star this post if you'd like to learn about the Denisovans as well!
Until next time :)
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