Where did the Neanderthals go?
(Part I and II)
(first part)
Neanderthals were originally thought not to have developed language like humans, but simply to "talk" to each other by muttering. To modern humans (Homo sapiens) they were as "other" as wild animals. Their extinction was thought to have been caused by modern man's genocide in a war for control of resources. The popular BBC documentary series "BBC History of the World" also shows the last Neanderthal being speared to death by modern humans. However, the results of molecular biology and molecular genetics research in this regard are different and very interesting. A summary is provided.
In 2005, scientists at the University of Pennsylvania published their research on the FOXP2 gene. The relatively high rate of mutations in this gene was of interest to scientists. Moreover, defects in this gene cause defects in the power of speech, so the main role of this gene in the power of speech is certain. When the FOXP2 gene was removed from the DNA of experimental mice, not only their ability to produce sound was affected, but defects were also found in the structure of the brain. In the next step, scientists replaced the FOXP2 gene extracted from the DNA of mice by inserting the human FOXP2 gene. Not only did the mice's voice change, but changes were also seen in the circuits in their brain cells that are similar to humans. I am responsible for speech. When the human FOXP2 gene protein was compared to the corresponding chimpanzee protein, only two sites showed small changes. That is, these two changes are the reason for the presence of speech in humans and its absence in chimpanzees. In 2010, DNA was obtained from a Neanderthal fossil bone found in southern Siberia and its genome was sequenced. The genome is made up of DNA and contains all the genes of an organism and the elements that regulate those genes. When the Neanderthal FOXP2 gene was examined, the protein it produced was similar to that of modern humans. There was absolutely no difference between the two. If the protein is not different, then the brain circuits responsible for speech will not be different. This means that Neanderthals were not just wandering creatures. They could speak and had the ability to coexist with modern humans.
In modern humans, CBFA1 is a gene that, if mutated, causes a disease called cleidocranial dysplasia, which results in a protruding and prominent forehead, a jersey-like overall structure of the ribs, and Neanderthal-like shoulders. A change in the same gene has led to the obvious difference between modern humans and Neanderthals.
But why would modern humans have thought of Neanderthals as "other" when they looked not too different from modern humans and could even speak like modern humans? Why would their race be extinct? Where did the Neanderthals go?
Next post for the rest.
#Evolution_Stories
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Where did the Neanderthals go?
(second part)
In 2014, a team of American and German scientists published a report comparing the Thousand Genomes Project and Neanderthal genomes. Recall that the "Thousand Genome Project" was an international genetics project in which the genomes of 1,000 people from around the world were to be sequenced. However, due to the cheapness of the technology during the project, the costs were much lower than estimated and the genomes of 2400 people were sequenced instead of 1000 (96 of them were also from Pakistan). The results of this comparative research are very interesting. According to the report, Africans are the "most genetically pure" modern humans in the world. Between 2 and 3 percent (up to 4 percent, according to some researchers) of all human genomes outside of Africa contain fragments of Neanderthal DNA. If these "fragments" of Neanderthal DNA present in modern humans were collected, about 40 percent of the Neanderthal genome could still be recovered today. This simply means that Neanderthals and modern humans assimilated and had extensive sexual intercourse. In such a case, the possibility of any bloody genocide is negligible. According to population genetics experts, this peaceful coexistence between the two species lasted from about 65,000 years ago to 47,000 years ago. And over the next 15,000 years or so, the Neanderthals were extinct.
Thanks to genes inherited through sexual contact from Neanderthals, the skin of modern humans from Africa was able to withstand the cold climate of Europe. However, the genes for blood cholesterol, schizophrenia (commonly known as delusional disease), heart disease and, according to some scientists, blood sugar and smoking addiction also came from Neanderthals (not necessarily because Neanderthals smoked). A study of the genome of Neanderthals shows that they had a tendency to marry close relatives (cousin marriages). Maybe that's whyApart from the above-mentioned diseases, other diseases also accumulated in them with time. Are these diseases the cause of their extinction? maybe not. These diseases can be a cause but not the only cause.
Examining human DNA, genes expressed in the male reproductive organs (testes) contain almost no Neanderthal DNA. Which means their male reproductive organs were not as fertile as modern humans and lost out to modern human reproductive organs in "natural selection". Furthermore, modern humans have almost no Neanderthal DNA on their X chromosomes. Since the majority of genes that cause reproductive failure in organisms other than humans are found on the X chromosome, the absence of Neanderthal DNA on this human chromosome reinforces the idea that Neanderthals were less fertile. . This can be considered as one of the major reasons for the extinction of the Neanderthals.
Some scientists also believe that, due to living in isolation for almost two hundred thousand years, Neanderthals underwent genetic changes that were harmless to them but fatal to the hybrid species resulting from mixing with modern humans. In the language of genetics, such changes are called Dobzhansky-Müller incompatibilities (DMIs). Such changes have already been reported in various organisms. Therefore, the hybrid individuals who inherited the DNA with these changes from Neanderthals did not survive. could live while the descendants of people who inherited DNA related to modern humans remained. As a result, Neanderthals became extinct over time. However, there is a difference of opinion among scientists in this regard.
In addition, some scientists attribute the low resistance of Neanderthals to infectious diseases as a major reason for their extinction compared to modern humans. However, I leave this topic to those working on infectious diseases. Neanderthals, however, may not have gone extinct for any single reason. As new techniques and information become available over time, we will need to look back frequently. The main purpose of these two posts was to highlight the utility of molecular biology and genetics and the scientific method in the study of history. Hopefully, new questions will arise in your mind.
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