About six centuries ago, the bubonic plague known as Black death claimed tens of millions of lives in a short period of time in Europe and North Africa. This great plague wiped out up to 60% of Europe’s population at that time.
At that time medical technology was still simple. Only people who can adapt are able to survive in the midst of a plague caused by bacteria Yersinia pestis that. This leaves an observable trail of natural selection by scientists today in the human population.
Research on malaria cases in Africa also shows the process of natural selection. Some populations survive the attack of this disease, some die and are replaced.
Will a similar story of natural selection occur in the COVID-19 pandemic which in the last year and a half has claimed a number of victims? more than 4.1 million people around the world? Could COVID-19 be a triggering factor for natural selection in humans? May be.
A latest study published In early May, involving nearly 50,000 COVID-19 patients from nineteen countries, they mapped a significant association between clinical symptom severity and a cluster of genetic variants associated with at least eight genes in the human genome.
The results of this research suggest certain variations in these genes that can “make” us susceptible to severe illness, or we can survive.
Plague and natural selection
From about 192 million people who are now infected with COVID-19, the majority of cases have mild symptoms. Only about 15% have severe symptoms causing acute respiratory syndrome with Irregular immune response.
The largest proportion of deaths related to COVID-19 is indeed in elderly patients or patients who have comorbid conditions. However, many deaths also occur in adults and children without comorbidities.
Although the mechanism of susceptibility to COVID-19 is still not fully understood, host (human) immune and genetic factors may play a role in causing differences in the level of infection. disease severity COVID-19. For example, people who have an immune response Interferon tipe I stronger, can better defend against acute infection.
Like the plague influenza pada 1918, host genetic factors play an important role in defense against flu viruses currently observable in European populations. Certain genetic variants found abundantly in Western European populations in the gene IFITM3 aids resistance to infection with the influenza A virus, whose pathology is very similar to that of the H1N1 virus infection of the 1918 outbreak.
Meanwhile, a genomic study in the Rroma gypsy population in Europe sheds light on the evidence genetic adaptation to bubonic plague. The researchers compared autosomal genetics in a Romanian Rroma gypsy population isolated from the general European population, with a European (non-gypsy) Romanian population. The bacteria that caused the bubonic plague also infected the Rroma population in Europe at the time, but not in its native India.
The estimated Roma gypsy population come from South Asia, to be precise in northern India, at ~1,500 years ago. They migrated to Europe about five centuries later.
The Rroma gypsy population has a different genetic background from the European Romanian population, but has the same exposure to the bubonic plague. Interestingly, genetic studies have shown that there is evidence of natural selection in four genes in the genome of the Rroma population that are similar to the current European Romanian population. However, evidence of natural selection was not observed in its native population in northern India.
Three of them are gene complexes TLR, who can recognize Yersinia pestis (causes bubonic plague) and plays a role in defense against pathogens.
Black death occurred in the middle of the 14th century. Bacteria Yersinia pestis which causes the paste to be spread by fleas (Xenopsylla cheopsis) in rats carried on slave ships, originating in the Crimea, and traveling around the Mediterranean region.
We are survivors
Humans have walked on this earth for at least 300,000 thousand years, a journey that is not short.
Humans leave Africa around 60,000-50,000 years ago, through various geographical and climatic conditions.
Since then, humans have (and continue to) undergo intense biological adaptations to their environment. Researchers have been able to decipher evidence of the natural selection process in human DNA.
Only people who have survivor DNA can survive in the environment they are in. They live, reproduce, and pass their DNA on to their offspring. Others will die or be knocked out and move on.
In addition to geographical conditions, the endemicity of diseases and pandemics in the past has become one of the determining factors for the direction of human evolution.
In addition to the pandemics caused by viruses and bacteria above, the pressure of malaria endemicity in Africa has shaped the genomes of human populations in sub-Saharan Africa to date.
The Plasmodium parasite, the cause of malaria spread by the Anopheles mosquito, has been living side by side with humans for ~100,000 years. The increase in malaria deaths in the last ~10,000 years as a result of the spread of agricultural culture eventually led to the apparent evolution and natural selection of human populations.
Currently, according to WHO report, 94% of the total cases due to malaria in 2019 in the world occurred in Africa, as many as 215 million cases.
However, populations in Africa, especially the sub-Saharan population, also have a high frequency of red blood cell disorders, such as Sickle-cell Trait (sickle-shaped red blood cell disorder), thalassemia, and hemoglobinopati (red blood cell disorders related to hemoglobin production). This is what gave birth “malaria hypothesis” from JBS Haldane, one of the pioneers of modern population genetics in 1949. He revealed that the high frequency of red blood cell disorders Sickle Cell is a natural selection response to malaria stress.
Several years after, AC Allison confirmed the hypothesis and states that individuals with Sickle Cell resistant to malaria. The cause, a nucleotide mutation in the gene HBB change the structure of red blood cells. This change can inhibits adhesion Plasmodium falciparum to blood cells and prevent infection.
Natural selection work
If a human pair had four children, the population would double in 25-30 years. Their number will continue to increase exponentially.
However, there are external factors that suppress the population, such as disasters, environmental changes, and disease outbreaks.
This “environmental pressure” factor is one of the factors that maintains the sustainability of the population. Certain types of species can survive despite environmental pressures, while others are eliminated, disappear, and die.
Of the many findings in observations during his exploration, Alfred R. Wallace dan Charles Darwin concluded that only those who can adapt to their environment can survive. Survival of the fittest, once we get to know him.
With so many variations in physical and genetic characteristics within the same species, the environment will play a role in determining which variations are suitable for living in it.
Nature chooses, nature chooses. That’s what happened in the case of the bubonic plague, malaria, and maybe later the COVID-19 pandemic.
However, the COVID-19 pandemic is not over yet so it is not possible to know for sure the “power” of natural selection caused by this pandemic in humans. Is current vaccine technology actually slowing down the pace of natural selection due to COVID-19?
The next generation of researchers who can examine the phenomena of natural selection and human evolution due to COVID-19.
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