ネアンデルタールとニコティン中毒 - Living, Loving, Thinking, Again

Tim Radford “Neanderthal DNA may account for nicotine addiction and depression” https://www.theguardian.com/science/2016/feb/11/neanderthal-dna-may-account-for-nicotine-addiction-and-depression

ホモ・サピエンスとネアンデルタール人の間に混血が起こり、現代のヨーロッパ人と亜細亜人はネアンデルタール人の遺伝子を受け継いでいることが確認されたのは2010年のことだが*1、米国のヴァンダービルト大学のJohn Anthony Capra氏*2を中心とするティームの研究によると、そのネアンデルタール人由来の遺伝子が私たちの、ketatosisという日焼けによる皮膚癌*3、ニコティンへの依存症、鬱病に関係している可能性が高いという。

Corinne N. Simonti, Benjamin Vernot, Lisa Bastarache, Erwin Bottinger, David S. Carrell, Rex L. Chisholm, David R. Crosslin, Scott J. Hebbring, Gail P. Jarvik, Iftikhar J. Kullo, Rongling Li, Jyotishman Pathak, Marylyn D. Ritchie, Dan M. Roden, Shefali S. Verma, Gerard Tromp, Jeffrey D. Prato, William S. Bush, Joshua M. Akey, Joshua C. Denny, and John A. Capra “The phenotypic legacy of admixture between modern humans and Neandertals” http://science.sciencemag.org/content/351/6274/737

「要旨」に曰く、

Many modern human genomes retain DNA inherited from interbreeding with archaic hominins, such as Neandertals, yet the influence of this admixture on human traits is largely unknown. We analyzed the contribution of common Neandertal variants to over 1000 electronic health record (EHR)–derived phenotypes in ~28,000 adults of European ancestry. We discovered and replicated associations of Neandertal alleles with neurological, psychiatric, immunological, and dermatological phenotypes. Neandertal alleles together explained a significant fraction of the variation in risk for depression and skin lesions resulting from sun exposure (actinic keratosis), and individual Neandertal alleles were significantly associated with specific human phenotypes, including hypercoagulation and tobacco use. Our results establish that archaic admixture influences disease risk in modern humans, provide hypotheses about the effects of hundreds of Neandertal haplotypes, and demonstrate the utility of EHR data in evolutionary analyses.

『ガーディアン』の記事に戻って；

“Our main finding is that Neanderthal DNA does influence clinical traits in modern humans,” said John Capra, an evolutionary geneticist at Vanderbilt University in Nashville, Tennessee. “We discovered associations between Neanderthal DNA and a wide range of traits, including immunological, dermatological, neurological, psychiatric and reproductive diseases.”
Sub-Saharan African peoples do not inherit Neanderthal DNA. The assumption is that the Neanderthals left Africa first, had time to adapt to a colder, darker and more difficult world, evolved paler skin colour to take advantage of less certain sunlight, and developed other traits that might have helped them survive changing conditions.
Early modern humans – more gracile, and perhaps quicker to adapt and take advantage of their environment – then migrated north from Africa to outpace and outlive the first Europeans. But, during the thousands of years the two species coexisted, they also interbred.
And these encounters passed on traits that might have been of some evolutionary advantage in an Ice Age world. But in changing conditions, the same lengths of inherited DNA contained greater health liabilities as well.
One of these, the researchers think, was a Neanderthal gene variant that increases blood-clotting. This would have sealed wounds more quickly, and prevented infection more easily. But in a modern western society, hyper-coagulation brings other problems, including greater risk for stroke, pulmonary embolism and pregnancy complications.
One length of Neanderthal DNA is now linked to increased risk of nicotine addiction, and several variants influence the risk of mood disorders, including depression. As tobacco was introduced into widespread use in Europe only 400 years ago, the researchers were surprised at the number of Neanderthal genetic variants now associated with modern psychiatric and neurological disorders.

煙草が所謂旧大陸に伝わり・普及したのはコロンブス以降じゃないかと一瞬思ったのだが、最初に洗練された煙草文化をつくった米大陸の先住民はネアンデルタール系の遺伝子を引き継ぐ亜細亜人だったわけだ。でも、ここで鍵となるのは寒くて日照の少ない環境への適応ということなのだが、それとニコティンへの依存との関係は納得できない。

*2:See eg. https://medschool.vanderbilt.edu/cqs/people/John%20Anthony%20%28Tony%29/Capra/cqs-faculty-members

*3:See eg. “What Is Actinic Keratosis?” http://www.skincancer.org/skin-cancer-information/actinic-keratosis/what-is-actinic-keratosis https://en.wikipedia.org/wiki/Actinic_keratosis https://ja.wikipedia.org/wiki/%E6%97%A5%E5%85%89%E8%A7%92%E5%8C%96%E7%97%87