Close to destruction
According to Chinese scientists, the African population of the ancestors of Homo sapiens is about 900 thousand people. Years ago it decreased dramatically, and traces of this can still be seen in our genes. – This is the so-called bottleneck effect when a large part of the population dies and is then reborn from a small number of individuals – explains Dr. Martina Mulak from the Laboratory of Paleogenetics at the University of Warsaw, who specializes in ancient DNA research. Modern human genes must have been used to trace this distant event, because fossil DNA can only survive for tens of thousands of years at most. Chinese scientists analyzed the DNA of 3,000 people with a computer. People living today using the FitCoal method, which combines information obtained from DNA with demographic models, have examined how many ancient ancestors from which modern human DNA comes.
From these calculations, scientists concluded that the number is approximately 930,000. Years ago, the number of human ancestors shrank by up to 98.6%. At one point in time in all of Africa, there were only 1,280 individuals left capable of breeding! And it remained that way for the next 100,000 years. Years. Paleontologists have also noted traces of this event. At that time, all fossil traces of our ancestors were almost completely lost in Africa, and neither bones nor man-made tools were found.
almost. 930,000 years ago, the number of human ancestors shrank by up to 98.6%. – say scientists from Shanghai
Our ancestors came close to extinction not only in Africa – and based on climate and paleontological data, scientists from the Natural History Museum in London determined that a similar catastrophic event occurred 200,000 years ago. Years ago in Europe, it was inhabited by representatives of the species Homo erectus and Homo heidelbergensis. almost. 1.1 million years ago, four thousand years ago, Europe became very cold due to a North Atlantic cooling spell. This has led to the disappearance of traces of the existence of early human species. Homo erectus reappeared in Europe only 200,000 years ago. After years. About half a million years ago it turned into a Neanderthal – a Neanderthal.
It was similar in Africa. After more than 100 thousand years of bottleneck only 800 thousand. Years ago, there was a rapid increase in the number of representatives of the human race. According to scientists, this event, which almost led to the extinction of our ancestors, could be a breakthrough in human evolution. – At such moments, when the population is very small, genetic mutations carrying new traits have a greater chance of becoming permanent – explains the professor. Ewa Bartnik, geneticist from the University of Warsaw. A new trait is created when two people carrying the same mutation meet and pass it on to their offspring. – If the mutation prefers to survive in a changed environment, the offspring carrying it will survive and reproduce – says the professor. Bartnik.
According to the team of Prof. He’s from Shanghai, this is what happened during the 900K bottleneck. Years ago. Hence, the mutation in the genes responsible for increased brain size could have become permanent, because – according to paleontological data and fossil research – it occurred during this period. At that time, Homo erectus mastered fire and began preparing nutritious meals, which led to increased brain development and cognitive abilities. Thanks to this, some people at that time survived the drought and emerged unscathed from the climatic catastrophe. In a research paper published in one of the latest issues of “Science” magazine, the professor’s team said. He also suggests that there may be another mysterious change in our genes, the formation of chromosome 2, which has always intrigued geneticists. – This is a big difference between us and apes – they have 48 chromosomes, while we only have 46, and chromosome 2 was most likely created from a combination of the other two. Until now, it is not known when and under what circumstances this happened – explains the professor. Bartnik.
Conquests and disasters
Such episodes of rapid population decline are written into the genes of Homo sapiens. The oldest thing that scientists have discovered occurred about 70 thousand years ago. Years ago. This bottleneck in the history of our species was discovered by geneticists from Stanford University in the United States and the Russian Academy of Sciences. They analyzed microsatellites – short, repetitive segments of DNA with a high rate of mutations, that is, errors that are transmitted from generation to generation. Therefore, the study of small satellites is a useful tool for reconstructing the history of various human groups living in the world. From this study, which was conducted on the DNA of people from 52 regions in the world, scientists concluded that from 70,000 people years ago, the number of Homo sapiens decreased to only 2,000! Why? According to prof. Michael R. Rampino of New York University, the near-total extinction of Homo sapiens was caused by the eruption of the giant Toba volcano in Sumatra 74,000 years ago. Years ago. It was one of the most powerful volcanic eruptions in our planet’s known history, spewing ash into the air and then cutting off the Earth from sunlight for months, causing a volcanic winter and cold climate across the planet. Which lasted up to a thousand years.
However, not all paleontological research confirms this hypothesis. As scientists from the Australian University of Queensland have shown, this effect was not particularly pronounced in India, and at the newly discovered Daba fossil site in northern India there are no traces of a decline in the number of people in the period 80-50 thousand. Years ago. Years ago. In Africa, there are no radical climate changes in this period, as the professor suggests. Rampino. Therefore, scientists today believe that the bottleneck effect at that time was caused by the migration of Homo sapiens from Africa. – A very small part of the population living in Africa has migrated to Europe and Asia – says Dr. Martina Mulak. According to estimates by geneticists, several thousand people arrived in Asia Minor and split into two main groups – one moved east and settled in Asia and Australia, the other north towards Europe.
Today, scientists believe that the fact that so few of our ancestors left Africa is the main reason why we are almost identical from a genetic standpoint. – Almost all people living in the world outside of sub-Saharan Africa have very similar DNA. Genetically, for example, the average Chinese person is more similar to an Englishman than two people from different tribes in Nigeria, Dr. Molak says. Indigenous peoples living in the Americas are genetically more homogeneous. These are the descendants of Homo sapiens, who arrived on the North American continent about 13,000 years ago. Years ago, when lower sea levels in the last ice age made it possible to cross from the Chukchi Peninsula into Alaska via a land bridge called Beringia. 11 thousand years ago, Beringia disappeared after being submerged by rising ocean waters. – There were a relatively small number of people who moved to the new land, and then were cut off from the rest of the world for thousands of years – explains Dr. Molak.
The presence of a very small set of genes in the population also increases the risk of genetic diseases. This is what happened to the isolated Native Americans living in what is now the province of Quebec. – In this population, a rare genetic condition called lipoprotein lipase deficiency is 100 times more common than in people in other parts of the world. In genetics, we call this founder effect. It arises when the entire population comes from a small number of ancestors, which often happens after a bottleneck effect – says the professor. Ewa Bartnik.
The emergence of both influences was facilitated by the increasing additional migrations of Homo sapiens around the world, but also by a culture that prohibited interbreeding with people outside a given group. Therefore, in the last 10 thousand years ago, many genetically homogeneous societies appeared in the world – as the professor proved. Priya Moorjani of the University of California, Berkeley. Perhaps the best scientifically studied example is the Ashkenazi Jews, whose number declined to only 1,000 people about 1,000 years ago. Today this group includes more than 10 million descendants. Ashkenazi Jews currently make up 80 percent. The number of Jewish population in the world, and before World War II, the percentage was 92 percent. As genetic research proves, although they live in many places in the world, they are still genetically homogeneous.
They include populations that have recovered from an episode with very low numbers – according to the results of Prof. Moorjani – also Finns or the indigenous people of Easter Island, who experienced a sharp population decline in the 17th century when European colonists arrived on Rapa Nui. – We discovered the founding influence in many peoples that we had not suspected, for example in the inhabitants of ancient Morocco or Siberia. As a Frenchman, I was surprised to find this effect in the Basques, says geneticist Remy Tournebez of the University of Berkeley, co-author of this study.
The bubonic plague epidemic of the 14th century was one of the last events to significantly reduce the population, and according to today’s estimates up to 60 percent lost their lives at that time. Population of Europe, and it took 150 years to rebuild the population. Although it was not a suffocation episode, thanks to evolutionary mechanisms, humanity emerged from this disaster with additional advantages that facilitated survival. This was discovered by geneticists from McMaster University in Canada, who analyzed DNA samples of people who lived before, during and after the plague pandemic – for a hundred years. They identified four genes that protect against the disease. One of these genes was the ERAP2 gene, two identical copies of which provided double the chance of survival compared to other variants, because they made the immune system more effective at killing the Yersinia pestis bacillus that causes plague. Those with protective variants in their genes survived. Genes that protect against plague have survived in the DNA of Europeans to this day.
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