In this article we report our interview with two professors: professor Jacopo Moggi Cecchi, from Univertisy of Florence and Olga Rickards from University of Tor Vergata Roma, about our link with the Neanderthal genes and the consequences of hybridization with Sapiens.
In the past most of the scientists thought that between Neanderthal and H. sapiens there was a lot of competition; now, thanks to genetic studies, we know that the two species actually reproduced and mixed between themselves. In favour of this thesis scientists found out that, in the human population, we all have 2% neanderthal DNA.
First question: from studies done, we know that Homo Sapiens and Neanderthal were morphologically different. How was it possible for them to communicate and interact, despite all their differences?
1st Answer:
JMC: "about this question, we are almost entering in ipothesis and speculation. Probably the communication wasn't in the form of language, but in other different ways. The two species didn't have the same ways on language and then they couldn't really comprehend each others. However, all this, didn't stop them to interact, as the genetic proves it".
OR: "Look at the third answer".
Second question: in the animal world, the ibridation between two different species not always ha a positive response, most of the times we don't have a fertile offspring. How can we explain this positive result?
2nd Answer:
JMC: "It was probably in the initial stage of a genetic isolation process, in fact these two species had still the ability to reproduce and give birth to fertile hybrids. A good example, from the present, are some different species of African baboons. These have different distribution areas, but at the overlapping margins and then individuals of different species can hybridize".
OR: "Recent molecular studies have highlighted that in the animal kingdom hybridization between distinct taxonomic units, i.e. between different species, is a common phenomenon not only in captivity but also in nature in the overlapping areas of the distribution area where a incomplete reproductive isolation. Examples are the fertile mating between polar bears and brown bears, between wolves and coyotes, and between different primate species. Thus Denisova, Neanderthals and Homo sapiens, although they are three different species with different phyogenetic and biogeographical histories, have mated in the contact areas and produced fertile offspring as demonstrated by the presence of archaic genome in the current populations of our species."
Third question: What do we know about neanderthal sequenced genes in the human genome?
3rd Answer:
JMC: "it was observed that the distribution of neanderthal DNA fragments in the human genome, in present indivuduals, is not homogeneous. Scientists haven't found any neanderthal contribution in some specific genom region, for example the chromosome X and in othe important funtional areas. This trend, together with the fact that percentages of the neanderthal genome from present individuals are the same as the ones found in 45,000 thousands years ago human genomes, let us think that an important negative selection occured thanks to hybridization events. Contrariwise, some of the archaic genomic regions that have been retained in modern genomes, appear to have conferred evolutionary advantage on H. sapiens population, during their spread across Eurasia. Signals of positive selection towards the neanderthal alleles have been highlighted, for example, in genes concerning pigmentation, robustness of the skin and hair, restistence to pathogens. While a variant of the EPASI gene, which regulates the concentration of hemoglobin in the bloos as a response to hypoxia, and is present in high-altitude Tibetan populations, it derives from hybridization with Denisovans".
OR: "Neanderthal and Denisovan DNA traits are not uniformly distributed in the genome of modern human populations: areas rich in brain related genes poor in ancestral genome traits. Furthermore, Neanderthal and Denisovan ancestry is not present in the X chromosome and in the genes expressed in the testis: the introduction of these archaic DNA traits would have reduced fertility in males, as observed in nature in hybrids between highly divergent groups of the same species or between different species. In contrast, the areas of the genome where traits derived from Neanderthals or Denisovans are concentrated are the regions involved with blood sugar levels, fat metabolism, and the immune system well known as a target of evolution. This is a phenomenon known as adaptive introgression. Indeed, the hybridization of our species with the Denisovans and Neanderthals, who had lived in the Eurasian area for hundreds of thousands of years, would have allowed our ancestors from Africa to quickly acquire those more suitable variants, both immune and environmental, to survive in the new lands they were colonizing.It would appear that Denisovan genes are linked to a more acute sense of smell in the Papuans of New Guinea and more efficient adaptation to high altitudes in the Tibetans. While the Neanderthal genes distributed among populations in the world would probably have contributed to having more resistant skin and hair and therefore to making migrants from Africa better tolerate the rigid temperatures of high latitudes.
Another advantageous variant inherited from Neanderthals is the V660L of the PGR gene which on chromosome 11 codes for the progesterone receptor, the hormone secreted by the corpus luteum in the ovary during the second half of the menstrual cycle, important for preparing the uterine lining for egg implantation and for maintaining early pregnancy. Women who have low progesterone levels during pregnancy are at risk of miscarriage and bleeding in the first trimester. Nearly one in three women of European descent carry the genetic variant that has a favorable effect on fertility (10 times more than any other genome trait). In fact, its carriers have greater fertility, more children, fewer miscarriages and less bleeding during the first pregnancy. Specifically, out of 24,000 modern women of European descent, 29% carry one copy of the Neanderthal variant and 3% carry two. In fact, its carriers have greater fertility, more children, fewer miscarriages and less bleeding during the first pregnancy. Thus, the progesterone receptor is an example of how favorable genetic variants that were introduced into modern humans through admixture with Neanderthals can have effects today.
However, intermingling with Neanderthals has not always proved successful. In fact, it would seem that an archaic genomic segment of ~50 kb, transmitted to us by Neanderthals, could cause in carrier individuals an increased risk of falling ill with severe forms of SARS-CoV-2. This haplotype of Neanderthal origin is almost completely absent in Africa, in southern Asia it has a frequency of 30%, in Europe it is 8%, and it has lower frequencies in eastern Asia. The highest incidence is found in Bangladesh, where more than half of the population (63%) carries a copy of the variant.
However, a recent study identified a variant located on chromosome 12 and present in 3 Neanderthals that reduces the risk of developing severe cases of COVID-19 by 22%. The variant is currently present in about half of individuals living outside Africa."
Fourth question: Couldn't the extinction of the Neanderthals has been caused by several different factors, such as the competition and mixing with Sapiens, but also the probable high inbreeding (endogamy) wich leads to the manifestation of recessive allelic diseades?
4th Answer:
JMC: "Surely different factors have contributed to the extinction of Neanderthals, and among these probably phenomena of endogamy. However the big role is played by the low genetic variabilty in the Neanderthal populations".
OR: "Surely the disappearance of Neanderthals from the evolutionary scene is due to various causes (I would not speak of extinction given the presence of Neanderthal genome traits in us): anatomical differences (especially at the level of the organization of the brain that has led us to the development of those brain areas connected with the activities assigned to creative thinking, social functions and competition for resources, which has made us evolutionarily advantaged), climate change, environmental deterioration, low numbers, arrival of modern man."
Fifth question: How and how much does the Neanderthal heritage affect our susceptibility to covid-19?
JMC:"Question at the limit of my competence. See here.
https://ilbolive.unipd.it/index.php/it/news/covid19-alcuni-geni-ereditati-dai-neanderthal"
OR:"Admixture with Neanderthals has not always proved successful. In fact, it would seem that an archaic genomic segment of ~50 kb, transmitted to us by Neanderthals, could cause in carrier individuals an increased risk of falling ill with severe forms of SARS-CoV-2. This haplotype of Neanderthal origin is almost completely absent in Africa, in southern Asia it has a frequency of 30%, in Europe it is 8%, and it has lower frequencies in eastern Asia. The highest incidence is found in Bangladesh, where more than half of the population (63%) carries a copy of the variant.
However, a recent study identified a variant located on chromosome 12 and present in 3 Neanderthals that reduces the risk of developing severe cases of COVID-19 by 22%. The variant is currently present in about half of individuals living outside Africa."
We hope that you enjoyed this reading and we thank again the professor Jacopo Moggi Cecchi and Olga Rickards for his time and kindness.
