How did people come about?
From the book by Andrey Sokolov and Tatiana Sokolova "The world and humans for students and their parents".
How did people come about?
People appeared on Earth as a result of evolution, just like all other living organisms that surround us: grasses and mushrooms, snakes and lizards, crocodiles and turtles, whales and penguins, apple and pine trees, roses and cacti.
What is evolution?
Evolution is a process that has been going on on Earth for over 4 billion years and will continue as long as life exists on our planet.
Evolution is a process as a result of which from microscopic bubbles that could multiply and create living organisms similar to themselves, flowers, trees, birds, fish, animals and humans arose.
Evolution is a constant process of random changes in any living organism, leading either to the disappearance (extinction) of this living organism, or to the appearance in the organism of new useful signs that allow it to successfully survive. In addition, it also happens that the ongoing changes do not have any significant impact on the survival of the organism.
Evolution is a process when, without any conception and plan, by trial and error, as a result of random changes inside the cells of the body and under the influence of all kinds of external factors, changes constantly occur in living organisms, leading to the disappearance of some living beings and the appearance of completely new that weren't there before.
Evolution is random changes in the structure of an organism that can be inherited by next generations. Moreover, in these generations, only such traits are fixed and transmitted further that do not interfere with the survival of the entire species as a whole. Sometimes new traits even help the species gain significant advantages over other types of living creatures, but this happens quite rarely.
The most ancient creatures on Earth are the ancestors of microscopic archaea, bacteria and unicellular eukaryotic organisms - our great-great-great-relatives. Scientists do not know what they looked like and can only roughly guess what kind of organic matter they were able to create. This knowledge in all living organisms is stored in special molecules - DNA (sometimes in RNA). Each such molecule has many small pieces (genes), each of which stores information on how to make a substance useful for this organism. And most importantly, living things are able to pass on this RNA or DNA by inheritance - to their children, grandchildren, great-grandchildren.
If you take a school ruler, a meter tape with divisions from a sewing kit, or even better - a large tape measure from a tool store, then on all of them you can see the same stripes denoting millimeters and centimeters. Imagine that each centimeter is a separate gene that contains information about a special substance - a protein that is required to create one of the parts of your body: hair, bone, skin, heart or brain.
In fact, everything, of course, is much more complicated and every cell of the skin, bone or heart consists of many substances and proteins, but it is important for us to understand the principle.
And if we go back to the tape measure, then the millimeter strips from 0 to 1 cm will contain instructions about one protein, and the stripes from 1 to 2 cm will contain instructions on another protein.
Of course, this analogy is also not entirely correct and is only a diagram. But a real RNA or DNA molecule is not a store tape.
By the way, the difference between RNA and DNA can also be explained by the example of a 30-centimeter school ruler. RNA is just one ruler. And DNA is two, placed side by side so that the 0 mark on one ruler is opposite the 30 mark on the other.
In order to understand how millimeter stripes on a tape measure or a ruler can contain information on how to build a cell, an organ and the entire body as a whole, we have to go back to the store and go to the checkout.
The salesperson at the checkout passes the item through a scanner, which reads the barcode placed on the purchase label. And while the parents are paying and checking the change, take a look at this barcode. These are just stripes of different thicknesses, located at different distances from each other. But these stripes, if you know how to read them, contain information about where and who made this product, what kind of product it is, what size, weight, color it is, what is it called and there is even a special strip for checking whether the scanner has correctly read all this information.
In DNA and RNA, everything is about the same. Each strip on the ruler is like a dash on a barcode, only in the case of a molecule - these dashes are pieces of DNA, denoted by the letters A, T, G and C, or RNA, where the letters will be A, U, G, C.
These letters, repeating and alternating, create a biological cipher, which contains all the information about how to build an organism and how to regulate its growth and development.
It may seem fantastic to us how you can write down information about every
living organism on Earth - a plant, a microbe or an animal - in four
letters. It seems impossible that just four letters would define all the
features and differences of an elephant from a hummingbird, a crocodile from
a person, a tree from a dolphin, a microscopic bacteria from a whale shark,
and an apricot from a mosquito.
But if we digress from the book for a minute and see if we have received an SMS, we will find that all the information that we now receive from the phone, smartphone, the Internet, everything that is stored by parents on the computer, everything that can be found on Facebook, Instagram or YouTube, everything that we watch on TV and much and much more is encrypted and transmitted to us with just two characters - zero and one. And now the possibilities of nature, encrypting its information with four symbols, no longer seem so unrealistic to us.
Now we know how our most ancient ancestors were able to convey information to us. More precisely, not exactly to us. They passed it on to their children, and those to their own. Etc. But the most tricky thing is that this information changed a little during the transmission. It is this process of change that is evolution.
How do these changes take place?
The fact is that when copying information from parents to children, from cell to cell as a result of reproduction and division, errors constantly occur. These mistakes can be neutral - and then nothing special happens. They can be dangerous - and then the new organism dies. May be helpful. And then the organism may develop adaptations useful for survival - eyes, horns, fangs or legs.
In addition, genes, the information code of living organisms are constantly influenced by all sorts of external influences, which also leads to a change in the sequence of letters in the cipher, and therefore to the emergence of new building molecules that can be neutral, fatal or useful.
This can be compared to copying homework from notebook to notebook. Every scribe may not be careful enough and make one or two mistakes. And someone may accidentally miss a letter or number. It can even change the meaning of the word. The next scribe may or may not notice the error and correct it.
In addition, in the process of such copying, especially if it is done not with a ballpoint pen, but with a fountain pen, then you can put a blot under which a letter or a word will disappear entirely.
As a rule, the result of such a rewriting, if it is done hundreds and thousands of times, will be that the first student will receive a good grade, and the one who copied the last will receive a bad one. In nature, this is most often the case. But sometimes a notebook falls into the hands of a good student and he not only corrects all the mistakes made by the scribes, but also finds a better solution for the entire homework, which at first, the very first student did not find. And it is in this case that significant beneficial changes occur in nature - elephants have a trunk, a giraffe has a long neck, monkeys understand how to walk on two legs, and human ancestors have a large brain and a special structure of the hand, which helps to firmly hold a hammer, bicycle steering wheel and ballpoint pen.
But how, as a result of these random changes, a person appeared from a microscopic bubble with a tiny DNA molecule?
First you need to understand that this process took many, many millions of years. More precisely, more than four billion years. And the result of this process - the appearance of man - is nothing more than a series of accidents that could well have not happened, and then there would be no man on Earth, but intelligent dinosaurs would live, playing on dinosaur computers and writing dinosaur poems. And maybe there would be no dinosaurs, but there would be a naked Earth and an ocean teeming with huge balls-colonies, similar to floating anthills and eating everything that comes their way.
But a series of random changes in the sequences and alternations of the letters A, T, G and C in the DNA molecule, over billions of years led not to the formation of six-legged furry unicorns, but to the appearance of man.
But first there was the ocean. And in the ocean lived microorganisms that did not even use the oxygen that we breathe, and without which we cannot live. On the contrary, these microorganisms excreted oxygen as an unnecessary and by-product of their life. Literally, they went to their ocean toilet and gave off oxygen.
Gradually, so much of this oxygen accumulated that those microorganisms survived and multiplied that learned not to emit this oxygen, but to use it. And this happened due to changes in the genetic barcode of their DNA. And it took evolution about one billion years.
Over the next billions and millions of years, microorganisms continued to change under the influence of external factors and errors in copying the genetic barcode. Some organisms remained unicellular, others gathered in colonies and gradually turned into multicellular algae and various marine animals, and still others, climbed inside these primitive animals and plants and learned to live and feed on another living creature, turning into parasites.
And all these billions of years, animals have been looking for food, multiplying, passing on traits and codes by inheritance and eating creatures of their own kind or completely different from themselves, but quite suitable for food. And those who, thanks to constant changes in the genome, could get more food for themselves, and those who, thanks to other changes in the genome, could effectively hide, protect themselves or run away from those who wanted to eat them, survived. The rest of the animal species died.
Plants, the genetic code of which also changed, changed in parallel. Some plants died out, others successfully multiplied and at some point, as a result of ebbs and flows, droughts and floods, ended up on land. First near the sea, then farther and farther from it. And the Earth became not only blue, but also green.
Following the plants, in search of food and safety, sea animals also began to get out on land. And after the herbivorous animals, predators also got out on land.
Of course, in order to make landfall, both plants and animals had to endure very great changes. Plants, for example, have a trunk, and animals have limbs.
And at first nothing foreshadowed the possibility of a man's appearance. The first rulers of the Earth for several hundred million years were reptiles and insects.
Now we are admiring dragonflies, brushing off flies and mosquitoes, catching butterflies and lizards. But 300 and even 60 million years ago everything would have been exactly the opposite. And it is unlikely that huge reptiles and giant insects would admire the little men on the shore of the pond. Rather, they would hunt them and chew them thoroughly.
And it is not known what would have happened if, as a result of another accident, giant reptiles, i.e. dinosaurs are not extinct.
Meanwhile, even during the reign of the dinosaurs, about 200 million years ago, small animals appeared - the ancestors of modern mammals.
For 140 million years, our four-legged ancestors hid from huge lizards and came out of hiding in search of food only at night.
But not only hiding. The evolution continued. And by the end of the reign of dinosaurs, our ancestors had already become very similar to modern animals, carrying their young inside the mother's body. And about 30 million years before the end of the dinosaur era, i.e. about 90 million years ago, our direct ancestors appeared - primates. We usually call them monkeys, but this is not quite the correct term. Monkeys are just one type of primate.
The extinction of the dinosaurs allowed mammals to finally come out of hiding places and turn into huge mammoths, elegant giraffes, agile monkeys and formidable lions.
Mammals, including our great-great-great-great-primate ancestors, have changed, multiplied, populated and left various geographic areas of the Earth for about another 40 million years. And so, about 18 million years ago, a species of primates appeared, which we now call hominids, i.e. humanoid. Four large groups of hominids have survived to this day: chimpanzees, gorillas, humans and orangutans.
Somewhere 11 million years after the appearance of the hominids, i.e. 7 million years ago, some of the groups of these animals learned to walk on two legs. But before the appearance of modern man, it was still far away. Evolution took another 5 million years for random changes to lead to the emergence of the genus Homo, i.e. people. It happened about 2 million years ago.
But even here the modern Homo Sapiens "Intelligent" or "Smart" - the species to which both the authors and readers of this book belong, did not appear immediately. Before us, evolution created Homo "Straight", who managed to tame fire and learned how to cook food on a fire, and Neanderthals, who invented the first clothes.
By the way, for the sake of justice, it should be noted that the first stone tools - scrapers, knives, etc. It was not we, Homo "Smart" who invented at all, but the Australopithecines, which appeared 3.5 million years ago, i.e. more than 3 million years before us.
Our species of hominids is Homo Sapiens, i.e. a kind of primates, narrow-nosed monkeys, appeared in Africa about 250-400 thousand years ago. And for some time we existed on Earth simultaneously with several other Homo species, including the Neanderthals. But then the rest of the species died out and about 40 thousand years ago we were left alone.