An interesting service has appeared on the global network (dinosaurpictures.org), which allows you to see what our planet looked like 100, 200, ... 600 million years ago. A list of events occurring in the history of our planet is given below.

Nowadays
. There are practically no places left on Earth that are not affected by human activity.

20 million years ago
Neogene period. Mammals and birds are beginning to resemble modern species. The first hominids appeared in Africa.

35 million years ago
The middle stage of the Pleistocene in the era of the Quaternary period. In the course of evolution, small and simple forms of mammals evolved into larger, more complex and diverse species. Primates, cetaceans and other groups of living organisms develop. The earth is cooling, and deciduous trees are spreading. The first species of herbaceous plants evolve.

50 million years ago
Beginning of the tertiary period. After an asteroid destroyed the dinosaurs, surviving birds, mammals and reptiles evolved to occupy the vacated niches. A group of cetacean ancestors branches off from land mammals and begins to explore the oceans.

65 million years ago
Late Cretaceous. Mass extinction of dinosaurs, marine and flying reptiles, as well as many marine invertebrates and other species. Scientists are of the opinion that the cause of the extinction was the fall of an asteroid in the area of ​​the present Yucatan Peninsula (Mexico).

90 million years ago
Cretaceous period. Triceratops and Pachycephalosaurs continue to roam the Earth. The first species of mammals, birds and insects continue to evolve.

105 million years ago
Cretaceous period. Triceratops and Pachycephalosaurs walk around the Earth. The first species of mammals, birds and insects appear.

120 million years ago
Early Cretaceous. The land is warm and humid, and there are no polar ice caps. The world is dominated by reptiles; the first small mammals lead a semi-hidden lifestyle. Flowering plants evolve and spread throughout the Earth.

150 million years ago
The end of the Jurassic period. The first lizards appeared, primitive placental mammals evolved. Dinosaurs dominate all land. The world's oceans are inhabited by marine reptiles. Pterosaurs become the dominant vertebrates in the air.

170 million years ago
Jurassic period. Dinosaurs are thriving. The first mammals and birds evolve. Ocean life is diverse. The climate on the planet is very warm and humid.

200 million years ago
Late Triassic. As a result of mass extinction, 76% of all species of living organisms disappear. Population sizes of surviving species are also greatly reduced. Species of fish, crocodiles, primitive mammals, and pterosaurs were less affected. The first real dinosaurs appear.

220 million years ago
Middle Triassic. The Earth is recovering from the Permian-Triassic extinction event. Small dinosaurs begin to appear. Therapsids and Archosaurs appeared along with the first flying invertebrates.

240 million years ago
Early Triassic. Due to the death of a large number of land plant species, there is a low oxygen content in the planet's atmosphere. Many species of corals have disappeared, and many millions of years will pass before coral reefs begin to rise above the surface of the Earth. Small ancestors of dinosaurs, birds and mammals survive.

260 million years ago
Late Perm. The largest mass extinction in the history of the planet. About 90% of all species of living organisms disappear from the face of the Earth. The disappearance of most plant species leads to the starvation of a large number of species of herbivorous reptiles, and then predators. Insects are deprived of their habitat.

280 million years ago
Permian period. The landmasses merge together to form the supercontinent Pangea. Climatic conditions are deteriorating: polar ice caps and deserts are beginning to grow. The area suitable for plant growth is sharply reduced. Despite this, four-legged reptiles and amphibians are diverging. The oceans abound with various species of fish and invertebrates.

300 million years ago
Late Carboniferous. Plants develop a developed root system, which allows them to successfully colonize hard-to-reach areas of land. The area of ​​the Earth's surface occupied by vegetation is increasing. The oxygen content in the planet's atmosphere is also increasing. Life begins to actively develop under the canopy of ancient vegetation. Evolving the first reptiles. A wide variety of giant insects appear.

340 million years ago
Carboniferous (Carboniferous period). There is a mass extinction of marine organisms on Earth. Plants develop a more advanced root system, which allows them to more successfully invade new land areas. The concentration of oxygen in the planet's atmosphere is increasing. The first reptiles evolve.

370 million years ago
Late Devonian. As plants develop, life on land becomes more complex. A large number of insect species appear. Fish develop strong fins that eventually develop into limbs. The first vertebrates crawl onto land. The oceans abound with corals, various species of fish, including sharks, as well as sea scorpions and cephalopods. The first signs of a mass extinction of marine life are beginning to appear.

400 million years ago
Devonian. Plant life on land becomes more complex, accelerating the evolution of terrestrial animal organisms. Insects diverge. The species diversity of the World Ocean is increasing.

430 million years ago
Silur. The mass extinction wipes out half of the species diversity of marine invertebrates from the face of the planet. The first plants begin to colonize the land and populate the coastal strip. Plants begin to develop a conducting system that accelerates the transport of water and nutrients to tissues. Marine life is becoming more diverse and abundant. Some organisms leave reefs and settle on land.

450 million years ago
Late Ordovician. The seas are teeming with life, and coral reefs appear. Algae are still the only multicellular plants. There is no complex life on land. The first vertebrates appear, including jawless fish. The first harbingers of mass extinction of marine fauna appear.

470 million years ago
Ordovician. Marine life becomes more diverse and corals appear. Seaweeds are the only multicellular plant organisms. The simplest vertebrates appear.

500 million years ago
Late Cambrian. The ocean is simply teeming with life. This period of rapid evolutionary development of many forms of marine organisms was called the “Cambrian Explosion”.

540 million years ago
Early Cambrian. Mass extinction is taking place. During evolutionary development, marine organisms develop shells and an exoskeleton. Fossil remains indicate the beginning of the Cambrian Explosion.

One of the curves showing sea level fluctuations over the past 18,000 years (the so-called eustatic curve). In the 12th millennium BC. sea ​​level was about 65 m lower than today, and in the 8th millennium BC. - already at less than 40 m. The rise in level occurred quickly, but unevenly. (According to N. Morner, 1969)

The sharp drop in sea level was associated with the widespread development of continental glaciation, when huge masses of water were withdrawn from the ocean and concentrated in the form of ice in the high latitudes of the planet. From here, glaciers slowly spread towards the middle latitudes in the northern hemisphere on land, in the southern hemisphere - along the sea in the form of ice fields that overlapped the shelf of Antarctica.

It is known that in the Pleistocene, the duration of which is estimated at 1 million years, three phases of glaciation are distinguished, called in Europe Mindel, Ries and Würm. Each of them lasted from 40-50 thousand to 100-200 thousand years. They were separated by interglacial eras, when the climate on Earth became noticeably warmer, approaching the modern one. In some episodes, it became even 2-3° warmer, which led to the rapid melting of ice and the release of vast areas on land and in the ocean. Such dramatic climate changes were accompanied by equally dramatic fluctuations in sea level. During the era of maximum glaciation, it decreased, as already mentioned, by 90-110 m, and during interglacial periods it increased to +10... 4-20 m compared to the current one.

The Pleistocene is not the only period during which significant fluctuations in sea levels occurred. Essentially, they mark almost all geological epochs in the history of the Earth. Sea level has been one of the most unstable geological factors. Moreover, this has been known for quite a long time. After all, ideas about transgressions and regressions of the sea were developed back in the 19th century. And how could it be otherwise, if in many sections of sedimentary rocks on platforms and in mountainous folded areas, clearly continental sediments are replaced by marine ones and vice versa. Sea transgression was judged by the appearance of remains of marine organisms in the rocks, and regression was judged by their disappearance or the appearance of coals, salts or red flowers. By studying the composition of faunal and floristic complexes, they determined (and are still determining) where the sea came from. The abundance of thermophilic forms indicated the invasion of waters from low latitudes, the predominance of boreal organisms indicated transgression from high latitudes.

The history of each specific region had its own series of transgressions and regressions of the sea, since it was believed that they were caused by local tectonic events: the invasion of sea waters was associated with the subsidence of the earth's crust, their departure with its uplifting. When applied to the platform areas of the continents, on this basis a theory of oscillatory movements was even created: cratons either sank or rose in accordance with some mysterious internal mechanism. Moreover, each craton obeyed its own rhythm of oscillatory movements.

It gradually became clear that transgressions and regressions in many cases occurred almost simultaneously in different geological regions of the Earth. However, inaccuracies in paleontological dating of certain groups of layers did not allow scientists to come to a conclusion about the global nature of most of these phenomena. This conclusion, unexpected for many geologists, was made by American geophysicists P. Weil, R. Mitchum and S. Thompson, who studied seismic sections of the sedimentary cover within the continental margins. Comparison of sections from different regions, often very distant from one another, helped to reveal the confinement of many unconformities, breaks, accumulation or erosional forms to several time ranges in the Mesozoic and Cenozoic. According to these researchers, they reflected the global nature of ocean level fluctuations. The curve of such changes, constructed by P. Weil et al., makes it possible not only to identify epochs of high or low standing, but also to estimate, of course to a first approximation, their scale. As a matter of fact, this curve summarizes the work experience of geologists of many generations. Indeed, you can learn about the Late Jurassic and Late Cretaceous transgressions of the sea or its retreat at the Jurassic-Cretaceous boundary, in the Oligocene and Late Miocene, from any textbook on historical geology. What was new, perhaps, was that these phenomena were now associated with changes in the level of ocean waters.

The scale of these changes was surprising. Thus, the most significant marine transgression, which flooded most of the continents in Cenomanian and Turonian times, is believed to have been caused by a rise in the level of ocean waters by more than 200-300 m above the modern one. The most significant regression that occurred in the Middle Oligocene is associated with a drop in this level by 150-180 m below the modern one. Thus, the total amplitude of such fluctuations in the Mesozoic and Cenozoic was almost 400-500 m! What caused such enormous fluctuations? They cannot be attributed to glaciations, since during the late Mesozoic and the first half of the Cenozoic the climate on our planet was exceptionally warm. However, many researchers still associate the mid-Oligocene minimum with the onset of a sharp cooling in high latitudes and with the development of the glacial shell of Antarctica. However, this alone was probably not enough to reduce the sea level by 150 m at once.

The reason for such changes was tectonic restructuring, which entailed a global redistribution of water masses in the ocean. Now we can only offer more or less plausible versions to explain fluctuations in its level in the Mesozoic and Early Cenozoic. Thus, analyzing the most important tectonic events that occurred at the turn of the Middle and Late Jurassic; as well as the Early and Late Cretaceous (which are associated with a long rise in water levels), we find that it was these intervals that were marked by the opening of large oceanic depressions. The Late Jurassic saw the emergence and rapid expansion of the western arm of the ocean, the Tethys (the region of the Gulf of Mexico and the Central Atlantic), and the end of the Early Cretaceous and most of the Late Cretaceous eras were marked by the opening of the southern Atlantic and many trenches of the Indian Ocean.

How could the formation and spreading of the bottom in young ocean basins affect the position of the water level in the ocean? The fact is that the depth of the bottom in them at the first stages of development is very insignificant, no more than 1.5-2 thousand m. The expansion of their area occurs due to a corresponding reduction in the area of ​​ancient oceanic reservoirs, which are characterized by a depth of 5-6 thousand. m, and in the Benioff zone, areas of the bed of deep-sea abyssal basins are absorbed. The water displaced from disappearing ancient basins raises the overall ocean level, which is recorded in land sections of the continents as sea transgression.

Thus, the breakup of continental megablocks should be accompanied by a gradual rise in sea level. This is exactly what happened in the Mesozoic, during which the level rose by 200-300 m, and perhaps more, although this rise was interrupted by eras of short-term regressions.

Over time, the bottom of young oceans became deeper and deeper as the new crust cooled and its area increased (the Slater-Sorokhtin law). Therefore, their subsequent opening had much less influence on the position of the ocean water level. However, it would inevitably lead to a reduction in the area of ​​the ancient oceans and even to the complete disappearance of some of them from the face of the Earth. In geology, this phenomenon is called the “collapsing” of the oceans. It is realized in the process of the rapprochement of continents and their subsequent collision. It would seem that the slamming of ocean basins should cause a new rise in water levels. In fact, the opposite happens. The point here is a powerful tectonic activation that covers converging continents. Mountain-building processes in the zone of their collision are accompanied by a general uplift of the surface. In the marginal parts of the continents, tectonic activation manifests itself in the collapse of blocks of the shelf and slope and their lowering to the level of the continental foot. Apparently, these subsidences also cover adjacent areas of the ocean floor, as a result of which it becomes much deeper. The overall level of ocean waters is falling.

Since tectonic activation is a one-act event and covers a short period of time, the drop in level occurs much faster than its increase during spreading of young oceanic crust. This is precisely what can explain the fact that sea transgressions on the continent develop relatively slowly, while regressions usually occur abruptly.

Map of possible flooding of Eurasian territory at various values ​​of the probable rise in sea level. The scale of the disaster (with the sea level expected to rise by 1 m during the 21st century) will be much less noticeable on the map and will have almost no impact on the lives of most states. The areas of the coasts of the North and Baltic Seas and southern China are enlarged. (The map can be enlarged!)

Now let's look at the issue of AVERAGE SEA LEVEL.

Surveyors leveling on land determine the height above “mean sea level.” Oceanographers who study sea level fluctuations compare them with elevations on the shore. But, alas, even the “long-term average” sea level is far from a constant value and, moreover, is not the same everywhere, and the sea coasts rise in some places and fall in others.

An example of modern land subsidence is the coasts of Denmark and Holland. In 1696, in the Danish city of Agger, there was a church 650 m from the shore. In 1858, the remains of this church were finally swallowed up by the sea. During this time, the sea advanced on land at a horizontal speed of 4.5 m per year. Now on the western coast of Denmark the construction of a dam is being completed, which should block the further advance of the sea.

The low-lying coasts of Holland are exposed to the same danger. The heroic pages of the history of the Dutch people are not only the struggle for liberation from Spanish rule, but also an equally heroic struggle against the advancing sea. Strictly speaking, here the sea does not advance so much as the sinking land recedes before it. This can be seen from the fact that the average high water level on the island. The Nordstrand in the North Sea rose by 1.8 m from 1362 to 1962. The first benchmark (altitude mark above sea level) was made in Holland on a large, specially installed stone in 1682. From the 17th to the mid-20th century, The soil subsidence on the Dutch coast occurred at an average rate of 0.47 cm per year. Now the Dutch are not only defending the country from the advance of the sea, but also reclaiming the land from the sea by building grandiose dams.

There are, however, places where the land rises above the sea. The so-called Fenno-Scandinavian shield, after being freed from the heavy ice of the Ice Age, continues to rise in our time. The coast of the Scandinavian Peninsula in the Gulf of Bothnia is rising at a rate of 1.2 cm per year.

Alternating lowering and rising of coastal land is also known. For example, the shores of the Mediterranean Sea sank and rose in places by several meters even in historical times. This is evidenced by the columns of the Temple of Serapis near Naples; marine elasmobranch molluscs (Pholas) have made passages in them to the height of human height. This means that from the time the temple was built in the 1st century. n. e. the land sank so much that part of the columns was immersed in the sea, and probably for a long time, since otherwise the mollusks would not have had time to do so much work. Later, the temple with its columns again emerged from the waves of the sea. According to 120 observation stations, over 60 years the level of the entire Mediterranean Sea has risen by 9 cm.

Climbers say: “We stormed a peak so many meters above sea level.” Not only surveyors and climbers, but also people completely unrelated to such measurements are accustomed to the concept of height above sea level. It seems to them unshakable. But, alas, this is far from the case. Ocean levels are constantly changing. It is fluctuated by tides caused by astronomical reasons, wind waves excited by the wind, and changeable like the wind itself, wind surges and water surges off the coast, changes in atmospheric pressure, the deflecting force of the Earth's rotation, and finally, the heating and cooling of ocean water. In addition, according to the research of Soviet scientists I.V. Maksimov, N.R. Smirnov and G.G. Khizanashvili, the ocean level changes due to episodic changes in the speed of rotation of the Earth and movement of its axis of rotation.

If you heat only the top 100 m of ocean water by 10°, the sea level will rise by 1 cm. Heating the entire thickness of ocean water by 1° raises its level by 60 cm. Thus, due to summer warming and winter cooling, sea level in the middle and high latitudes subject to noticeable seasonal fluctuations. According to the observations of the Japanese scientist Miyazaki, the average sea level off the western coast of Japan rises in the summer and falls in the winter and spring. The amplitude of its annual fluctuations is from 20 to 40 cm. The level of the Atlantic Ocean in the northern hemisphere begins to rise in the summer and reaches a maximum in winter; in the southern hemisphere, its reverse trend is observed.

The Soviet oceanographer A. I. Duvanin distinguished two types of fluctuations in the level of the World Ocean: zonal, as a result of the transfer of warm waters from the equator to the poles, and monsoon, as a result of prolonged surges excited by monsoon winds that blow from the sea to land in the summer and in in the opposite direction in winter.

A noticeable slope of sea level is observed in areas covered by ocean currents. It is formed both in the direction of the flow and across it. The transverse slope at a distance of 100-200 miles reaches 10-15 cm and changes with changes in current speed. The reason for the transverse inclination of the flow surface is the deflecting force of the Earth's rotation.

The sea also noticeably reacts to changes in atmospheric pressure. In such cases, it acts as an “inverted barometer”: more pressure means lower sea level, less pressure means higher sea level. One millimeter of barometric pressure (more precisely, one millibar) corresponds to one centimeter of sea level height.

Changes in atmospheric pressure can be short-term and seasonal. According to the research of the Finnish oceanologist E. Lisitsyna and the American one J. Patullo, level fluctuations caused by changes in atmospheric pressure are isostatic in nature. This means that the total pressure of air and water on the bottom in a given section of the sea tends to remain constant. Heated and rarefied air causes the level to rise, cold and dense air causes the level to fall.

It happens that surveyors conduct leveling along the seashore or overland from one sea to another. Having arrived at the final destination, they discover a discrepancy and begin to look for the error. But in vain they rack their brains - there may not be a mistake. The reason for the discrepancy is that the level surface of the sea is far from equipotential. For example, under the influence of prevailing winds between the central part of the Baltic Sea and the Gulf of Bothnia, the average difference in level, according to E. Lisitsyna, is about 30 cm. Between the northern and southern parts of the Gulf of Bothnia, at a distance of 65 km, the level changes by 9.5 cm. Between On the sides of the English Channel the difference in level is 8 cm (Creese and Cartwright). The slope of the sea surface from the Channel to the Baltic, according to Bowden's calculations, is 35 cm. The level of the Pacific Ocean and the Caribbean Sea at the ends of the Panama Canal, which is only 80 km long, differs by 18 cm. In general, the level of the Pacific Ocean is always slightly higher than the level of the Atlantic. Even if you move along the Atlantic coast of North America from south to north, a gradual rise in level of 35 cm is found.

Without dwelling on the significant fluctuations in the level of the World Ocean that occurred in past geological periods, we will only note that the gradual rise in sea level, which was observed throughout the 20th century, averages 1.2 mm per year. It is apparently caused by the general warming of the climate of our planet and the gradual release of significant masses of water that had been bound by glaciers until that time.

So, neither oceanographers can rely on the marks of surveyors on land, nor surveyors on the readings of tide gauges installed off the coast at sea. The level surface of the ocean is far from an ideal equipotential surface. Its exact definition can be achieved through the joint efforts of geodesists and oceanologists, and even then not before at least a century of simultaneous observations of vertical movements of the earth’s crust and sea level fluctuations at hundreds, even thousands of points have been accumulated. In the meantime, there is no “average level” of the ocean! Or, what is the same thing, there are many of them - each point has its own shore!

Philosophers and geographers of hoary antiquity, who had to use only speculative methods for solving geophysical problems, were also very interested in the problem of ocean level, although in a different aspect. We find the most specific statements on this matter in Pliny the Elder, who, by the way, shortly before his death while observing the eruption of Vesuvius, wrote rather arrogantly: “There is nothing in the ocean at present that we cannot explain.” So, if we discard the disputes of Latinists about the correctness of the translation of some of Pliny’s arguments about the ocean, we can say that he considered it from two points of view - the ocean on a flat Earth and the ocean on a spherical Earth. If the Earth is round, Pliny reasoned, then why don’t the waters of the ocean on its reverse side flow into the void; and if it is flat, then for what reason the ocean waters do not flood the land, if everyone standing on the shore can clearly see the mountain-like bulge of the ocean, behind which ships are hidden on the horizon. In both cases he explained it this way; water always tends to the center of the land, which is located somewhere below its surface.

The problem of sea level seemed insoluble two thousand years ago and, as we see, remains unresolved to this day. However, the possibility cannot be ruled out that the features of the level surface of the ocean will be determined in the near future by geophysical measurements made using artificial Earth satellites.

Gravity map of the Earth compiled by the GOCE satellite.
These days …

Oceanologists re-examined the already known data on sea level rise over the past 125 years and came to an unexpected conclusion - if throughout almost the entire 20th century it rose noticeably slower than we previously thought, then in the last 25 years it has grown at a very rapid pace, says the paper. article published in the journal Nature.

A group of researchers came to such conclusions after analyzing data on fluctuations in the levels of the Earth's seas and oceans during high and low tides, which have been collected in different parts of the planet using special tide gauge instruments for a century. Data from these instruments, as scientists note, are traditionally used to estimate sea level rise, but this information is not always absolutely accurate and often contains large time gaps.

“These averages do not reflect how the sea actually grows. Tire gauges are usually located along the coast. Because of this, large areas of the ocean are not included in these estimates, and if they are included, they usually contain large “holes,” Carling Hay from Harvard University (USA) is quoted in the article.

As another author of the article, Harvard oceanographer Eric Morrow, adds, until the early 1950s, humanity did not conduct systematic observations of sea levels at the global level, which is why we have almost no reliable information about how quickly the global sea level was rising. ocean in the first half of the 20th century.

Our planet is more than 4.5 billion years old. At the moment it appeared, it looked completely different. What happened in ancient times on the territory of modern Russia, and how it changed over the years - in the book “Ancient Monsters of Russia”.

3000 million years ago

In the first millions of years of its life, the Earth was like hell. There was constant acid rain here, and hundreds of volcanoes erupted. There were many more asteroids. Endless meteorite showers formed the planet - they crashed and became part of it. Some meteorites reached the size of modern cities.

One day, the Earth collided with another planet, one part of which joined us, and the second flew into orbit and over the years turned into the modern Moon.

Illustration from the book

3 billion years ago, a day lasted only 5 hours, and there were 1500 days in a year. A lunar eclipse occurred once every 50 hours, and a solar eclipse occurred once every 100 hours. It probably looked very beautiful, but there was no one yet to admire natural phenomena.

American biologists seem to have figured out why 100-74 thousand years ago humanity went through a bottleneck - its numbers sharply declined. Bacterial infections were to blame for this, killing people in infancy. Our ancestors managed to cope with them only by losing two genes that carried out “treacherous” activities.

It is possible that the influence of bacteria and viruses on the evolution of mammals and, in particular, humans is also significant. At least, according to scientists, they once helped us overcome the so-called “bottleneck.” Let me remind you that this is the name for a situation in which, for a variety of reasons, the population size and, accordingly, its genetic diversity sharply decrease. It is believed that this happened to people about 100-74 thousand years ago.

Then, according to anthropologists, the human population, which was already approaching a million, suddenly dropped sharply to 10-20 thousand individuals. And, what’s most interesting, almost all other representatives of the genus became extinct at the same time Homo, except for Neanderthals, and possibly Denisovans. It is still not entirely clear why this suddenly happened, although there were many versions. The most popular of them are the extinction of large ungulates that people hunted, as well as the consequences of the eruption of the Toba supervolcano on the island of Sumatra.

The last version, despite the fact that it is often presented on the pages of popular science books, is the weakest reasoned. Yes, of course, the eruption that happened 77.5 thousand years ago was powerful - the volcano threw out 800 cubic kilometers of ash alone. However, anthropologists have found traces of human settlements in East and South Asia after this event. That is, even the people who lived next to the volcano did not die out immediately. And besides, the decline in the number of the human race was not sharp - it began about 100 thousand years ago, that is, long before the eruption itself. So it could only hasten the extinction of many human groups, but was clearly not its cause.

As for the hypothesis that the “bottleneck” effect was associated with the extinction of large ungulates that were hunted by people, there is also some kind of temporary discrepancy. It is known that several such extinctions occurred during the Quaternary period, but none of them occurred at the indicated time. And besides, during the previous extinctions of large ungulates, no reduction in the number of people was observed - and in theory, it should have been if these two processes are related. In addition, anthropologists' data show that 100 thousand years ago, people still mainly hunted small animals, and not large ones.

So why did the population of people in those distant times decline so much? Biologists from the University of California at San Diego (USA) believe that the cause of this was epidemics caused by bacterial infections. However, according to their data, after a few tens of thousands of years, people were able to defeat these diseases - due to the fact that the genome of our ancestors got rid of two “traitor” genes that collaborated with harmful microorganisms.

Researchers were interested in two immune genes - Siglec-13 and Siglec-17. These DNA sequences help the immune system decide which immune cells to send to fight the pathogen. Both of these genes are known to be active in chimpanzees and gorillas, but they do not work in humans, since Siglec-17 is “turned off” as a result of a mutation, and its colleague number 13 is completely cut out from the genome.

After scientists synthesized the proteins encoded by these genes, they discovered an interesting thing - both proteins prevented antibodies from binding to antigens on the membranes of group B streptococci ( Streptococcus) and Escherichia coli K1 ( Escherichia coli). It turns out that if these proteins are present in immune cells, they will no longer recognize these bacteria as a potential threat to the body. And this led to catastrophic consequences. The fact is that the above-mentioned streptococci B and E. coli K1 are aggressive microbes that are very dangerous for newborns. After they enter the body, the child most often dies, and only modern medicines, which had not yet been invented 100 thousand years ago, can save him.

So, it turns out that about 400 thousand years ago, representatives of the genus Homo first became “acquainted” with these diseases. (This may have been due to changes in diet or habitat.) As a result, the population of our ancestors began to decline sharply, since most of them simply died in infancy. However, natural selection was also not asleep - according to genetic analysis, the “treacherous” genes Siglec-13 and Siglec-17 began to turn off between 400 and 270 thousand years ago, that is, even before modern humans split off from the branches of Neanderthals and Denisovans.

Thus, somewhere 270-265 thousand years ago, a certain population was formed, which consisted of individuals devoid of these molecular “traitors”. However, the infection was not dormant either. As people spread beyond Africa, she traveled with them. As a result, the number of all groups, except for the one that did not have genes dangerous to health, steadily decreased. The most intense extinction occurred just 100-74 thousand years ago. By the way, it is quite possible that it was spurred on by the Toba eruption or the reduction in the number of animals that people ate, because in a stressful situation any disease becomes more dangerous.

However, even for a population whose members had previously gotten rid of harmful genes, it took time for this change to become the general norm. It is therefore not surprising that the last traces of the Siglec-17 gene are found in some people. However, there are no such things on the planet now. If suddenly a reverse mutation occurs, which “turns on” this section of DNA during the development of the child, then he will not live to see a year.