Neandertals transmitted a taste for nicotine and a propensity to depression

Romantic encounters between Homo Sapiens and Neandertal have left their marks in the genome of modern Europeans, making many of us more prone to nicotine addiction and to depression.
 
Around 3% on average of the modern Europeans' genome is inherited from our Neandertal ancestors.  It may not seem like much (although we have not inherited more from our great-great-grand-mother) – but it packs a punch. It influences their risk of becoming addicted to nicotine as well as their tendency to depression, according to research published in Science magazine.
 
Corinne Simonti of Vanderbilt University in Nashville and her colleagues have analyzed the genome and disease data from 28,000 patients of European origins, which were collected for the Electronic Medical Records and Genomics (eMERGE) Network in the USA. For every single patient, the scientists were able to investigate how many and which segments of their genome contained Neandertal DNA. They subsequently compared which of these segments may be linked to which diseases. 

"Our major finding ist hat the DNA from Neandertals is  tied in with clinically significant characteristics of modern man,“ explains the senior author of the study, John Capra. Links have been found for diseases of the immune system, of the skin, but also of the nerves and brain.

Some of the findings confirm earlier assumptions – for instance, that the genetic makeup of the Neandertals made human skin less penetrable to UV light and to  pathogens. But the analysis also brought forth surprises, the authors write.

So that for instance a specific segment of the Neandertal genome is from all appearances heightening the risk for nicotine dependency. Additionally, a series of variants have been found, which influence the tendency to depression, positively as well as negatively. All in all, a surprisingly large number of the inherited segments are related to psychiatric or neurological effects.

It is probable that these segments provided, at first, advantages for survival, which is why they lingered on in the genome after modern humans, having left Africa some 50,000 years ago, mixed with the Neandertals farther North, the scientists explain. They conceivably imparted an adaptation to pathogens and to the different regimen of sunlight. "One night with a Neandertal was a small prize to pay for one thousand years of adaptation," means  Capra.

In today's environment, many of these genetic heirlooms may no longer bring any sizeable advantage, according to the scientists. Adducing as an example the genetic variant, inherited from the Neandertal, which brings increased blood clotting. This may have helped in earlier times to heal wounds faster, and to protect them from the intrusion of pathogens. Today, the consequences are rather negative, as they increase the risk for strokes, embolisms and complications in pregnancies.

"These are very interesting resuts,“ says Michael Dannemann of the Max-Planck-Institute for Evolutionary Anthropology in Leipzig, who did not take part in the new analysis himself. What might have been once the utility of the genome segments related to nicotine addiction is not easy to explain. ^{[Could it have been, because they were depressed? N. of Tr.]} It would be interesting, in his opinion, to make comparisons with the incidence of diseases in humans who do not have any Neandertal DNA – like the Africans. „Alas, there do not exist such good databanks for them as those which have been used in this study.“

Translated and adapted from the German by Anne-Marie de Grazia 

Der Spiegel, February 12, 2016

Six years ago, the scientists of the Max-Planck-Institute for Evolutionary Anthropology made worldwide headlines with the discovery that a little bit of the Neandertal is living on in modern Europeans. 

By comparing gene sequences, they established that within a time-window of between 47,000 to 65,000 years there occurred significant spates of interbreeding between homo sapiens and homo neanderthalensis.

This gave us Europeans a heritage of Neandertal genes which is estimated today to be between one and almost eight percent of our own individual genome. All in all, the population of Europe may have preserved over 20 percent of the Neandertal genome. And it is precisely characteristics which we consider as being „typically European“ which turn out to be typically Neandertal – light skin, braun, red or fair hair, maybe even freckles.

A new study published in the magazine Nature gives interesting details. The analysis of finds from the Altai mountains in Central Asia have shown that Neandertals lived there 100,000 year ago, in whose genome traces of ancestors of homo sapiens were found. From all evidence, the two human species had mated long before homo sapiens moved out of Africa. 

It is fairly sure that modern man und Neandertal met for the first time somewhere in the Levant, where Neandertal had been established for some ten thousands of years, when homo sapiens passed through on his way out of Africa.

Somewhere between Lebanon and the Arabic peninsula, some 100,000 years ago, occured the first interbreeding which has left traces in the genome. Sexual contacts were limited to some of the populations: so that Neandertal genes are found only among Europeans, Denisova genes among Asians (and Melanesians and Aborigines of Australia). Traces of the genome of European populations are to be found only among the Eastern Neandertalers – this particular kind of interbreeding does not seem to have occurred with Western Neandertals. 

The new studies contribute to an even greater upset of the alleged simplicity of the circumstances of the time when modern humans moved into Europe. In less than ten years, we have learned that in times barely prehistoric, three, four or more human species lived alongside each other in Eurasia. And traces of their contacts and of their romances are found in our genome today. This seems to describe situations characterized more by simultaneity and relatedness, than by descendance and inheritance: we are surviving brethren, rather than „descendants“ of the older species. 

The Neandertal was, just as we homo sapiens, probably a direct descendant of Homo erectus, who may have been the first representative of the human family to leave Africa (long, long before Homo Sapiens did so) and from whom developed the neanderthalensis and the possibly closely related Denisovans of Siberia, to the North, as well as the sapiens to the South.

Finds of these recent years show that all species met in Asia and in Europe. Most of the time, several species of humans lived in parallel with each others, and often in close proximity. It is not easy for us to retrospectively make out the boundaries between the species. And it appears that these boundaries are increasingly blurring.

Frank Patalong

Der Spiegel, February 17, 2016

Translated from the German and adapted by Anne-Marie de Grazia