The offspring of living beings are very similar to their parents. However, if the environment of living organisms changes, they can also change significantly. For example, if the climate gradually becomes colder, then some species may acquire increasingly thick hair from generation to generation. This process is called evolution. Over millions of years of evolution, small changes, accumulating, can lead to the emergence of new species of plants and animals that differ sharply from their ancestors.
How does evolution happen?
Evolution is based on natural selection. It happens like this. All animals or plants belonging to the same species are still slightly different from each other. Some of these differences allow their owners to better adapt to living conditions than their relatives. For example, some deer has particularly fast legs, and every time he manages to escape from a predator. Such a deer has a better chance of surviving and having offspring, and the ability to run quickly can be passed on to its cubs, or, as they say, inherited by them.
Evolution has created countless ways to adapt to the difficulties and dangers of life on Earth. For example, horse chestnut seeds over time acquired a shell covered with sharp spines. The spines protect the seed as it falls from the tree to the ground.
What is the rate of evolution?
Previously, these butterflies had light wings. They hid from enemies on tree trunks with the same light bark. However, about 1% of these butterflies had dark wings. Naturally, the birds noticed them immediately and, as a rule, ate them before others
Usually evolution proceeds very slowly. But there are cases when a species of animal undergoes rapid changes and spends not thousands and millions of years on this, but much less. For example, some butterflies have changed their color over the past two hundred years to adapt to new living conditions in areas of Europe where many industrial enterprises have arisen.
About two hundred years ago in Western Europe began to build coal-fired factories. The smoke from the factory chimneys contained soot, which settled on the tree trunks, and they turned black. Now the light-colored butterflies are more noticeable. But few butterflies with dark wings survived, because the birds no longer noticed them. From them came other butterflies with the same dark wings. And now most butterflies of this species living in industrial areas have dark wings.
Why do some animal species become extinct?
Some living things are unable to evolve when their environment changes dramatically, and die out as a result. For example, huge hairy animals similar to elephants - mammoths, most likely became extinct because the climate on Earth at that time became more contrasting: it was too hot in summer and too cold in winter. In addition, their numbers decreased due to intensive hunting of them by primitive man. And after the mammoths, saber-toothed tigers also became extinct - after all, their huge fangs were adapted to hunting only large animals like mammoths. Smaller animals were inaccessible to saber-toothed tigers, and, left without prey, they disappeared from the face of our planet.
How do we know that man also evolved?
Most scientists believe that humans evolved from tree-dwelling animals similar to modern monkeys. The proof of this theory is provided by certain structural features of our bodies, which allow us, in particular, to assume that our ancestors were once vegetarians and ate only fruits, roots and stems of plants.
At the base of your spine there is a bone formation called the tailbone. This is all that remains of the tail. Most of the hair covering your body is just soft fuzz, but our ancestors had much thicker hair. Each hair is equipped with a special muscle and stands on end when you are cold. It’s the same with all mammals with hairy skin: it retains air, which prevents the animal’s heat from escaping.
Many adults have wide outer teeth—they are called “wisdom teeth.” Now there is no need for these teeth, but at one time our ancestors used them to chew the tough plant foods they ate. The appendix is a small tube connected to the intestines. Our distant ancestors used it to digest plant foods that were poorly digestible by the body. Now it is no longer needed and is gradually becoming less and less. In many herbivores - for example, rabbits - the appendix is very well developed.
Can humans control evolution?
People drive evolution some animals have been around for over 10,000 years. For example, many modern breeds of dogs, in all likelihood, descended from wolves, packs of which roamed around the camps of ancient people. Gradually, those of them that began to live with people evolved into the new kind animals, that is, they became dogs. Then people began to specifically raise dogs for specific purposes. This is called selection. As a result, there are over 150 different dog breeds in the world today.
- Dogs that could be trained different teams, like this English Sheepdog, were bred to herd livestock.
- Dogs that could run fast were used to chase game. This greyhound has powerful legs and runs with huge leaps.
- Dogs with a good sense of smell were bred specifically for tracking game. This smooth-haired dachshund can tear apart rabbit holes.
Natural selection usually proceeds very slowly. Selective selection allows you to dramatically speed it up.
What is genetic engineering?
In the 70s XX century scientists have invented a way to change the properties of living organisms by interfering with them genetic code. This technology is called genetic engineering. Genes carry a kind of biological code contained in every living cell. It determines the size and appearance of every living creature. By using genetic engineering you can breed plants and animals that, say, grow faster or are less susceptible to some disease
In the article we will consider in detail the types of evolution, and also talk about this process in general, trying to comprehensively understand the topic. We will learn about how the doctrine of evolution originated, what ideas it is represented by, and what role the species plays in it.
Introduction to the topic
Evolution organic world is a rather complex and lengthy process that simultaneously takes place at different levels of organization of living matter. At the same time, it always touches on many areas. It so happened that the development of living nature occurs from lower to higher forms. Everything simple becomes more complicated over time and takes on a more interesting form. In certain groups of organisms, adaptation skills develop that allow living beings to better exist in their specific conditions. For example, some aquatic animals evolved membranes between their toes.
Three directions
Before talking about the types of evolution, let's consider the three main directions highlighted by the influential Russian scientists I. Shmalhausen and A. Severtsov. In their opinion, there is aromorphosis, idioadaptation, and degeneration.
Aromorphosis
Aromorphosis, or arogenesis, is a serious evolutionary change that generally leads to a complication of the structure and functions of some organisms. This process allows you to fundamentally change some aspects of life, for example, habitats. Also, aromorphosis helps to increase the competitiveness of specific organisms to survive in environment. The main point aromorphoses consists in the conquest of new adaptation zones. That is why such processes occur quite rarely, but if they do happen, they are of a fundamental nature and influence all further development.
In this case, it is necessary to understand such a concept as the adaptation level. This is a specific habitat zone with a characteristic climate and environmental conditions that are characteristic of certain group organisms. For example, for birds, the adaptive zone is the air space, which protects them from predators and allows them to learn new ways of hunting. In addition, movement in the air makes it possible to overcome large obstacles and carry out long-distance migrations. That is why flight is rightfully considered an important evolutionary aromorphosis.
The most striking aromorphoses in nature are multicellularity and the sexual method of reproduction. Thanks to multicellularity, the process of complicating the anatomy and morphology of almost all organisms began. Thanks to sexual reproduction, adaptive abilities have significantly expanded.
In animals, such processes contributed to the creation of more effective ways nutrition and improvement of metabolism. At the same time, the most significant aromorphosis in the animal world is considered warm-blooded, thanks to which survival has greatly increased in different conditions.
In plants, similar processes are manifested in the emergence of a general and conductive system that connects all their parts into a single whole. This increases pollination efficiency.
For bacteria, aromorphosis is an autotrophic mode of nutrition, thanks to which they were able to conquer a new adaptation zone, which may be deprived of organic food sources, but the bacteria will still survive there.
Idiomatic adaptation
Without this process it is impossible to imagine the evolution of biological species. It involves specific adaptations to specific environmental conditions. In order to better understand what this process is, let's think a little. Idioadaptation is small changes that significantly improve the life of organisms, but do not bring them to new level organizations. Let's consider this information using birds as an example. The wing is a consequence of the process of aromorphosis, but the shape of the wings and methods of flight are already idioadaptations that do not change the anatomical structure of birds, but are at the same time responsible for their survival in a certain environment. Such processes also include the coloring of animals. Because they significantly affect only a group of organisms, they are considered characteristics of species and subspecies.
Degeneration, or catagenesis
Macro- and microevolution
Now let's move directly to the topic of our article. What types of this process are there? This is micro and macro evolution. Let's talk about them in more detail. Macroevolution is the process of formation of the largest systematic units: species, new families, and so on. The main driving forces of macroevolution lie in microevolution.
Firstly, there is heredity, natural selection, variability and reproductive isolation. Divergent character is characteristic of micro- and macroevolution. At the same time, these concepts that we are talking about now have received a lot of different interpretations, but a final understanding has not yet been achieved. One of the most popular is that macroevolution is a change of a systemic nature that does not require large quantity time.
However, when it comes to learning this process, it takes a lot of time. Moreover, macroevolution is global in nature, so it is very difficult to master all its diversity. An important method for studying this area is computer modelling, which began to develop especially actively in the 1980s.
Types of Evidence for Evolution
Now let's talk about what evidence there is for macroevolution. Firstly, this is a comparative anatomical system of inferences, which is based on the fact that all animals have a single type of structure. This is what indicates that we all have common origin. Here, much attention is paid to homologous organs, as well as atavisms. Human atavisms are the appearance of a tail, multiple nipples and continuous hair. An important piece of evidence for macroevolution is the presence vestigial organs, which are no longer needed by a person and gradually disappear. The rudiments are the appendix, hairline and the remains of the third eyelid.
Now consider the embryological evidence, which is that all vertebrates have similar embryos to early stages development. Of course, over time, this similarity becomes less and less noticeable, as character traits for a certain type.
Paleontological evidence of the process of evolution of species lies in the fact that the remains of some organisms can be studied transitional forms other extinct creatures. Thanks to fossil remains, scientists can learn that transitional forms existed. For example, such a form of life existed between reptiles and birds. Also, thanks to paleontology, scientists were able to construct phylogenetic series in which one can clearly trace the sequence of successive species developing in the process of evolution.
Biochemical evidence is based on the fact that all living organisms on earth have a uniform chemical composition and genetic code, which should also be noted. Moreover, we are all similar in energy and plastic metabolism, as well as the enzymatic nature of some processes.
Biogeographical evidence is based on the fact that the process of evolution is perfectly reflected in the nature of the distribution of animals and plants on the surface of the Earth. Thus, scientists conditionally divided the planet’s massif into 6 geographical zones. We will not consider them in detail here, but we will note that there is a very close connection between the continents and related species of living organisms.
Through macroevolution, we can understand that all species evolved from previously living organisms. This reveals the essence of the development process itself.
Transformations at the intraspecific level
Microevolution refers to small changes in alleles in a population over generations. We can also say that these transformations occur at the intraspecific level. The reasons lie in mutation processes, artificial and natural drift and gene transfer. All these changes lead to speciation.
We have examined the main types of evolution, but we do not yet know that microevolution is divided into some branches. Firstly, this is population genetics, thanks to which the mathematical calculations necessary to study many processes are made. Secondly, this is environmental genetics, which allows us to observe development processes in reality. These 2 types of evolution (micro- and macro-) have great value and make a certain contribution to the development processes as a whole. It is worth noting that they are often contrasted with each other.
Evolution of modern species
First, let's note that this is an ongoing process. In other words, it never stops. All living organisms evolve from at different speeds. However, the problem is that some animals live for a very long time, so it is very difficult to notice any changes. Hundreds or even thousands of years must pass before they can be tracked.
IN modern world African elephants are actively evolving. True, with human assistance. Thus, the length of the tusk in these animals quickly decreases. The fact is that hunters have always hunted elephants, which had massive tusks. At the same time, they were much less interested in other individuals. Thus, their chances of survival and also of passing on their genes to other generations increased. That is why, over the course of several decades, a gradual decrease in the length of the tusks was observed.
It is very important to understand that the absence of external signs does not mean the end of the evolutionary process. For example, very often different researchers are mistaken about the lobe-finned fish coelacanth. There is an opinion that it has not evolved for millions of years, but this is not true. Let us add that today the coelacanth is the only living representative of the coelacanth order. If you compare the first representatives of this species and modern individuals, you can find many significant differences. The only similarity is in external signs. That is why it is very important to look at evolution comprehensively and not judge it solely by external signs. Interestingly, modern coelacanth has more similarities with the herring than with its ancestor, the coelacanth.
Factors
As we know, species arose through evolution, but what factors contributed to this? Firstly, hereditary variability. The fact is that various mutations and new combinations of genes create the basis for hereditary diversity. Note: the more active the mutation process, the more effective natural selection will be.
The second factor is the random preservation of features. To understand the essence of this phenomenon, let's understand concepts such as genetic drift and population waves. The latter are fluctuations that occur in periods and affect the population size. For example, every four years there are a lot of hares, and immediately after that their numbers drop sharply. But what is genetic drift? This means the preservation or disappearance of any signs in a random order. That is, if as a result of some events the population decreases greatly, then some characteristics will be preserved in whole or in part in a chaotic manner.
The third factor we will consider is the struggle for existence. Its reason lies in the fact that many organisms are born, but only some of them are able to survive. Moreover, there will not be enough food and territory for everyone. In general, the concept of the struggle for existence can be described as the special relationship of an organism with the environment and other individuals. There are several forms of struggle. It can be intraspecific, which occurs between individuals of the same species. The second form is interspecific, when representatives fight for survival different types. The third form is the fight against environmental conditions, when animals need to adapt to them or die. At the same time, the struggle within species is rightfully considered the most brutal.
We now know that the role of species in evolution is enormous. It is from one representative that mutation or degeneration can begin. However, the evolutionary process is regulated by itself, since the law of natural selection operates. So, if new signs are ineffective, then individuals that have them will die sooner or later.
Let's consider another important concept that is characteristic of all driving types of evolution. This is isolation. This term implies the accumulation of certain differences between representatives of the same population, which for a long time was isolated from each other. As a result, this can lead to the fact that individuals simply cannot interbreed with each other, thus creating two completely different species.
Anthropogenesis
Now let's talk about types of people. Evolution is a process characteristic of all living organisms. The part of biological evolution that led to the emergence of humans is called anthropogenesis. Thanks to this, separation occurred human species from great apes, mammals and hominids. What types of people do we know? Evolutionary theory divides them into Australopithecines, Neanderthals, etc. The characteristics of each of these species are familiar to us from school.
So we got acquainted with the main types of evolution. Biology can sometimes tell a lot about the past and present. That is why it is worth listening to her. Note: some scientists believe that 3 types of evolution should be distinguished: macro-, micro- and human evolution. However, such opinions are isolated and subjective. In this material, we presented to the reader 2 main types of evolution, thanks to which all living things develop.
To summarize the article, let's say that the evolutionary process is a real miracle of nature, which itself regulates and coordinates life. In the article we looked at the main theoretical concepts, but in practice everything is much more interesting. Every biological species is a unique system capable of self-regulation, adaptation and evolution. This is the beauty of nature, which took care not only of the created species, but also of those into which they can mutate.
Evolutionary doctrine
Evolutionary doctrine (theory of evolution)- a science that studies the historical development of life: causes, patterns and mechanisms. There are micro- and macroevolution.
Microevolution- evolutionary processes at the population level, leading to the formation of new species.
Macroevolution- evolution of supraspecific taxa, as a result of which larger systematic groups are formed. They are based on the same principles and mechanisms.
Development of evolutionary ideas
Heraclitus, Empidocles, Democritus, Lucretius, Hippocrates, Aristotle and other ancient philosophers formulated the first ideas about the development of living nature.
Carl Linnaeus believed in the creation of nature by God and the constancy of species, but allowed the possibility of the emergence of new species through crossing or under the influence of environmental conditions. In the book “System of Nature” C. Linnaeus substantiated the species as universal unit and the basic form of existence of living things; assigned a double designation to each species of animal and plant, where the noun is the name of the genus, the adjective is the name of the species (for example, Homo sapiens); described a huge number of plants and animals; developed the basic principles of taxonomy of plants and animals and created their first classification.
Jean Baptiste Lamarck created the first holistic evolutionary teaching. In his work “Philosophy of Zoology” (1809), he identified the main direction of the evolutionary process - the gradual complication of organization from lower to higher forms. He also developed a hypothesis about the natural origin of man from ape-like ancestors who switched to a terrestrial lifestyle. Lamarck considered the driving force of evolution to be the desire of organisms for perfection and argued for the inheritance of acquired characteristics. That is, organs necessary in new conditions develop as a result of exercise (giraffe’s neck), and unnecessary organs atrophy due to lack of exercise (mole’s eyes). However, Lamarck was unable to reveal the mechanisms of the evolutionary process. His hypothesis about the inheritance of acquired characteristics turned out to be untenable, and his statement about the internal desire of organisms for improvement was unscientific.
Charles Darwin created an evolutionary theory based on the concepts of the struggle for existence and natural selection. The prerequisites for the emergence of the teachings of Charles Darwin were the following: the accumulation by that time of rich material on paleontology, geography, geology, biology; selection development; advances in taxonomy; appearance cell theory; the scientist's own observations during circumnavigation on the Beagle. Charles Darwin outlined his evolutionary ideas in a number of works: “The Origin of Species by Natural Selection”, “Changes in Domestic Animals and Cultivated Plants under the Influence of Domestication”, “The Origin of Man and Sexual Selection”, etc.
Darwin's teaching boils down to this:
- each individual of a particular species has individuality (variability);
- Personality traits (although not all) can be inherited (heredity);
- individuals produce more offspring than survive to puberty and the beginning of reproduction, that is, in nature there is a struggle for existence;
- the advantage in the struggle for existence remains with the most adapted individuals, who have a greater chance of leaving behind offspring (natural selection);
- As a result of natural selection, the levels of organization of life gradually become more complex and species emerge.
Factors of evolution according to Charles Darwin- This
- heredity,
- variability,
- struggle for existence,
- natural selection.
Heredity
- the ability of organisms to transmit their characteristics from generation to generation (features of structure, development, function).
Variability
- the ability of organisms to acquire new characteristics.
Struggle for existence
- the whole complex of relationships between organisms and environmental conditions: with inanimate nature (abiotic factors) and with other organisms (biotic factors). The struggle for existence is not a "struggle" in literally words, in fact it is a survival strategy and a way of existence of an organism. There are intraspecific struggles, interspecific struggles and struggles against unfavorable environmental factors. Intraspecific struggle- fight between individuals of the same population. It is always very stressful, since individuals of the same species need the same resources. Interspecies fight
- struggle between individuals of populations of different species. It occurs when species compete for the same resources or when they are connected by predator-prey relationships. Struggle with unfavorable abiotic environmental factors especially manifests itself when environmental conditions deteriorate; intensifies intraspecific struggle. In the struggle for existence, the individuals most adapted to the given living conditions are identified. The struggle for existence leads to natural selection.
Natural selection- a process as a result of which predominantly individuals with hereditary changes that are useful under given conditions survive and leave behind offspring.
All biological and many other natural sciences were restructured on the basis of Darwinism.
Currently the most generally accepted is synthetic theory of evolution (STE). Comparative characteristics main provisions evolutionary doctrine Ch. Darwin and STE are given in the table.
Comparative characteristics of the main provisions of the evolutionary teachings of Charles Darwin and the synthetic theory of evolution (STE)
| Signs | Evolutionary theory of Charles Darwin | Synthetic theory of evolution (STE) |
| Main results of evolution | 1) Increasing the adaptability of organisms to environmental conditions; 2) increasing the level of organization of living beings; 3) increase in the diversity of organisms | |
| Unit of evolution | View | Population |
| Factors of evolution | Heredity, variability, struggle for existence, natural selection | Mutational and combinative variability, population waves and genetic drift, isolation, natural selection |
| Driving factor | Natural selection | |
| Interpretation of the term natural selection | Survival of the more fit and death of the less fit | Selective reproduction of genotypes |
| Forms of natural selection | Propulsive (and sexual as its variety) | Moving, stabilizing, disruptive |
The emergence of devices. Each adaptation is developed on the basis of hereditary variability in the process of struggle for existence and selection over a series of generations. Natural selection supports only expedient adaptations that help an organism survive and produce offspring.
The adaptability of organisms to the environment is not absolute, but relative, since environmental conditions can change. Many facts prove this. For example, fish are perfectly adapted to aquatic environment habitat, but all these adaptations are completely unsuitable for other habitats. Moths collect nectar from light-colored flowers, which are clearly visible at night, but often fly into the fire and die.
Elementary factors of evolution- factors that change the frequency of alleles and genotypes in a population ( genetic structure populations).
There are several basic elementary factors of evolution:
mutation process;
population waves and genetic drift;
insulation;
natural selection.
Mutational and combinative variability.
Mutation process leads to the emergence of new alleles (or genes) and their combinations as a result of mutations. As a result of mutation, a transition of a gene from one allelic state to another (A→a) or a change in the gene in general (A→C) is possible. The mutation process, due to the randomness of mutations, has no direction and cannot direct change without the participation of other evolutionary factors natural population. It only supplies elementary evolutionary material for natural selection. Recessive mutations in the heterozygous state constitute a hidden reserve of variability that can be used by natural selection when conditions of existence change.
Combinative variability arises as a result of the formation in descendants of new combinations of already existing genes inherited from their parents. The sources of combinative variability are the crossing of chromosomes (recombination), random divergence of homologous chromosomes in meiosis, and random combination of gametes during fertilization.
Population waves and genetic drift.
Population waves(waves of life) - periodic and non-periodic fluctuations in population size, both upward and downward. Population waves may be caused by periodic changes environmental factors environment (seasonal fluctuations in temperature, humidity, etc.), non-periodic changes (natural disasters), colonization of new territories by the species (accompanied by a sharp increase in numbers).
Population waves act as an evolutionary factor in small populations where genetic drift may occur. Genetic drift- random non-directional change in allele and genotype frequencies in populations. In small populations the effect random processes leads to noticeable consequences. If the population is small in size, then as a result random events some individuals, regardless of their genetic constitution, may or may not leave offspring, as a result of which the frequencies of some alleles can change dramatically over one or several generations. Thus, with a sharp reduction in population size (for example, due to seasonal fluctuations, reduction in food resources, fire, etc.), among the few surviving individuals there may be rare genotypes. If in the future the number is restored due to these individuals, this will lead to a random change in allele frequencies in the gene pool of the population. Thus, population waves are a supplier of evolutionary material.
Insulation is caused by the emergence of various factors that prevent free crossing. The exchange of genetic information between the resulting populations ceases, as a result of which the initial differences in the gene pools of these populations increase and become fixed. Isolated populations can undergo various evolutionary changes and gradually turn into different species.
There are spatial and biological isolation. Spatial (geographical) isolation associated with geographical obstacles (water barriers, mountains, deserts, etc.), and for sedentary populations and simply with long distances. Biological isolation is caused by the impossibility of mating and fertilization (due to changes in the timing of reproduction, structure or other factors that prevent crossing), death of zygotes (due to biochemical differences in gametes), sterility of the offspring (as a result of impaired chromosome conjugation during gametogenesis).
The evolutionary significance of isolation is that it perpetuates and enhances genetic differences between populations.
Natural selection. Changes in the frequencies of genes and genotypes caused by the evolutionary factors discussed above are random and non-directional. The guiding factor of evolution is natural selection.
Natural selection- a process as a result of which predominantly individuals with properties useful for the population survive and leave behind offspring.
Selection operates in populations; its objects are the phenotypes of individual individuals. However, selection based on phenotypes is a selection of genotypes, since it is not traits, but genes that are passed on to descendants. As a result, in the population there is an increase in the relative number of individuals possessing a certain property or quality. Thus, natural selection is the process of differential (selective) reproduction of genotypes.
Not only properties that increase the likelihood of leaving offspring are subject to selection, but also traits that are not directly related to reproduction. In some cases, selection may be aimed at creating mutual adaptations of species to each other (plant flowers and insects visiting them). Characters can also be created that are harmful to an individual, but ensure the survival of the species as a whole (a bee that stings dies, but by attacking an enemy, it saves the family). In general, selection plays creative role in nature, since from undirected hereditary changes those are fixed that can lead to the formation of new groups of individuals, more perfect in the given conditions of existence.
There are three main forms of natural selection: stabilizing, driving and disruptive (disruptive) (table).
Forms of natural selection
| Form | Characteristic | Examples |
| Stabilizing | Aimed at preserving mutations leading to less variability in the average value of a trait. It operates under relatively constant environmental conditions, that is, as long as the conditions that led to the formation of a particular characteristic or property remain. | Preservation of flower size and shape in insect-pollinated plants, since flowers must correspond to the body size of the pollinating insect. Conservation of relict species. |
| Moving | Aimed at preserving mutations that change the average value of a trait. Occurs when environmental conditions change. Individuals of a population have some differences in genotype and phenotype, and with long-term changes external environment an advantage in life activity and reproduction may be obtained by some individuals of the species with some deviations from average norm. The variation curve shifts in the direction of adaptation to new conditions of existence. | The emergence of resistance to pesticides in insects and rodents, and to antibiotics in microorganisms. Darkening of the color of the birch moth (butterfly) in developed industrial areas England (industrial melanism). In these areas, tree bark becomes dark due to the disappearance of lichens sensitive to air pollution, and dark moths are less visible on tree trunks. |
| Tearing (disruptive) | Aimed at preserving mutations that lead to the greatest deviation from the average value of the trait. Discontinuous selection occurs when environmental conditions change in such a way that individuals with extreme deviations from the average norm gain an advantage. As a result of discontinuous selection, population polymorphism is formed, that is, the presence of several groups that differ in some characteristic. | With frequent strong winds On oceanic islands, insects with either well-developed wings or rudimentary wings are preserved. |
A Brief History of the Evolution of the Organic World
The age of the Earth is about 4.6 billion years. Life on Earth originated in the ocean more than 3.5 billion years ago.
Short story development of the organic world is presented in the table. The phylogeny of the main groups of organisms is shown in the figure.
The history of the development of life on Earth is studied from the fossil remains of organisms or traces of their vital activity. They are found in rocks of different ages.
The geochronological scale of Earth's history is divided into eras and periods.
Geochronological scale and history of the development of living organisms
| Era, age (million years) | Period, duration (million years) | Animal world | World of plants | The most important aromorphoses |
| Cenozoic, 62–70 | Anthropogen, 1.5 | Modern animal world. Evolution and human dominance | Modern vegetable world | Intensive development of the cerebral cortex; bipedalism |
| Neogene, 23.0 Paleogene, 41±2 | Mammals, birds, and insects dominate. The first primates (lemurs, tarsiers) appear, later Parapithecus and Dryopithecus. Many groups of reptiles and cephalopods are disappearing | Flowering plants, especially herbaceous ones, are widespread; the flora of gymnosperms is declining | ||
| Mesozoic, 240 | Mel, 70 | Bony fish, protobirds, and small mammals predominate; Placental mammals and modern birds appear and spread; giant reptiles are dying out | Angiosperms appear and begin to dominate; Ferns and gymnosperms are declining | The emergence of flower and fruit. Appearance of the uterus |
| Yura, 60 | Giant reptiles, bony fish, insects, and cephalopods dominate; Archeopteryx appears; ancient cartilaginous fish are dying out | Modern gymnosperms dominate; ancient gymnosperms are dying out | ||
| Triassic, 35±5 | Amphibians, cephalopods, herbivores and predatory reptiles predominate; teleost fish, oviparous and marsupial mammals appear | Ancient gymnosperms predominate; modern gymnosperms appear; seed ferns are dying out | The appearance of a four-chambered heart; complete separation of arterial and venous blood flow; the appearance of warm-bloodedness; appearance of mammary glands | |
| Paleozoic, 570 | ||||
| Perm, 50±10 | Marine invertebrates, sharks, dominate; reptiles and insects develop rapidly; animal-toothed and herbivorous reptiles appear; Stegocephalians and trilobites become extinct | Rich flora of seed and herbaceous ferns; ancient gymnosperms appear; tree-like horsetails, mosses and ferns are dying out | Pollen tube and seed formation | |
| Carbon, 65±10 | Amphibians, mollusks, sharks, and lungfish dominate; winged forms of insects, spiders, and scorpions appear and quickly develop; the first reptiles appear; trilobites and stegocephals noticeably decrease | Abundance of tree ferns forming “coal forests”; seed ferns emerge; psilophytes disappear | The appearance of internal fertilization; the appearance of dense egg shells; keratinization of the skin | |
| Devon, 55 | Armored shellfish, mollusks, trilobites, and corals predominate; Lobe-finned, lungfish and ray-finned fish, stegocephals appear | Rich flora of psilophytes; mosses, ferns, mushrooms appear | Dismemberment of the plant body into organs; transformation of fins into terrestrial limbs; appearance of air breathing organs | |
| Silur, 35 | Rich fauna of trilobites, mollusks, crustaceans, corals; armored fish and the first terrestrial invertebrates (centipedes, scorpions, wingless insects) appear | Abundance of algae; plants come to land - psilophytes appear | Differentiation of plant body into tissues; division of the animal body into sections; formation of jaws and limb girdles in vertebrates | |
| Ordovician, 55±10 Cambrian, 80±20 | Sponges, coelenterates, worms, echinoderms, and trilobites predominate; jawless vertebrates (scutellates), mollusks appear | Prosperity of all departments of algae | ||
| Proterozoic, 2600 | Protozoa are widespread; all types of invertebrates and echinoderms appear; primary chordates appear - subtype Cranial | Widespread blue-green and green algae, bacteria; red algae appears | The emergence of bilateral symmetry | |
| Archeyskaya, 3500 | Origin of life: prokaryotes (bacteria, blue-green algae), eukaryotes (protozoa), primitive multicellular organisms | The emergence of photosynthesis; the appearance of aerobic respiration; emergence of eukaryotic cells; the appearance of the sexual process; emergence of multicellularity | ||
Evolution is a development process consisting of gradual changes, without sudden leaps (as opposed to revolution). Most often, when speaking about evolution, they mean biological evolution.
Biological evolution is the irreversible and directional historical development of living nature, accompanied by changes in the genetic composition of populations, the formation of adaptations, the formation and extinction of species, the transformation of ecosystems and the biosphere as a whole. Biological evolution is the study of evolutionary biology.
There are several evolutionary theories, which have in common the assertion that living forms of life are descendants of other life forms that existed previously. Evolutionary theories differ in their explanation of the mechanisms of evolution. IN this moment the most common is the so-called. synthetic theory of evolution, which is a development of Darwin's theory.
Genes that are passed on to offspring, as a result of expression, form the sum of the characteristics of an organism (phenotype). When organisms reproduce, their descendants develop new or changed characteristics that arise through mutation or the transfer of genes between populations or even species. In species that reproduce sexually, new combinations of genes arise through genetic recombination. Evolution occurs when heritable differences become more common or rare in a population.
Evolutionary biology studies evolutionary processes and puts forward theories to explain their causes. The study of fossils and species diversity had convinced most scientists by the mid-19th century that species change over time. However, the mechanism of these changes remained unclear until the publication in 1859 of the book On the Origin of Species by the English scientist Charles Darwin about natural selection as the driving force of evolution. Darwin and Wallace's theory was eventually accepted scientific community. In the 1930s, the idea of Darwinian natural selection was combined with Mendel's laws, which formed the basis of the synthetic theory of evolution (STE). STE made it possible to explain the connection between the substrate of evolution (genes) and the mechanism of evolution (natural selection).
Heredity
Heredity, the inherent property of all organisms to repeat the same signs and developmental features over a number of generations; is caused by the transfer during the process of reproduction from one generation to another of the material structures of the cell, containing programs for the development of new individuals from them. Thus, heredity ensures the continuity of the morphological, physiological and biochemical organization of living beings, their character individual development, or ontogeny. As a general biological phenomenon, heredity is the most important condition for the existence of differentiated forms of life, impossible without relative constancy characteristics of organisms, although it is disrupted by variability - the emergence of differences between organisms. Affecting a wide variety of traits at all stages of the ontogenesis of organisms, heredity manifests itself in the patterns of inheritance of traits, i.e., their transmission from parents to descendants.
Sometimes the term “Heredity” refers to the transmission from one generation to another of infectious principles (the so-called infectious heredity) or learning skills, education, traditions (the so-called social, or signaling, heredity). Such an expansion of the concept of heredity beyond its biological and evolutionary essence is controversial. Only in cases where infectious agents are able to interact with host cells up to the point of inclusion in their genetic apparatus, is it difficult to separate infectious inheritance from normal one. Conditioned reflexes are not inherited, but are developed anew by each generation, but the role of heredity in the speed of consolidation conditioned reflexes and behavioral characteristics are indisputable. Therefore, signal heredity includes a component of biological heredity.
Variability
Variability is the variety of characters and properties in individuals and groups of individuals of any degree of kinship. Inherent in all living organisms. Variation is distinguished between hereditary and non-hereditary, individual and group, qualitative and quantitative, directed and non-directed. Hereditary variability is caused by the occurrence of mutations, while non-hereditary variability is caused by the influence of environmental factors. The phenomena of heredity and variability underlie evolution.
Mutation
Mutation is a random, persistent change in the genotype that affects entire chromosomes, their parts or individual genes. Mutations can be large and clearly visible, for example, lack of pigment (albinism), lack of plumage in chickens, short toes, etc. However, most often mutational changes are small, barely noticeable deviations from the norm.
Mutations are a fairly rare event. The frequency of occurrence of individual spontaneous mutations is expressed by the number of gametes of one generation carrying a certain mutation, relative to total number gametes.
Mutations arise mainly as a result of two reasons: spontaneous errors in the replication of a nucleotide sequence and the action of various mutagenic factors causing replication errors.
Mutations caused by the action of mutagens (irradiation, chemical substances, temperature, etc.) are called induced, in contrast to spontaneous mutations that occur as a result of random errors in the action of enzymes that ensure replication, and/or as a result of thermal vibrations of atoms in nucleotides.
Types of mutations. Based on the nature of changes in the genetic apparatus, mutations are divided into genomic, chromosomal and gene, or point. Genomic mutations involve changing the number of chromosomes in the cells of the body. These include: polyploidy - an increase in the number of sets of chromosomes, when instead of the usual 2 sets of chromosomes for diploid organisms there can be 3, 4, etc.; haploidy - instead of 2 sets of chromosomes there is only one; aneuploidy - one or more pairs of homologous chromosomes are absent (nullisomy) or are represented not by a pair, but by only one chromosome (monosomy) or, conversely, by 3 or more homologous partners (trisomy, tetrasomy, etc.). Chromosome mutations, or chromosomal rearrangements, include: inversions - a section of a chromosome is turned 180°, so that the genes it contains are arranged in the reverse order compared to normal; translocations - exchange of sections of two or more non-homologous chromosomes; deletions - loss of a significant portion of a chromosome; deficiencies (small deletions) - loss of a small section of a chromosome; duplication - doubling of a chromosome section; fragmentation - breaking a chromosome into 2 or more parts. Gene mutations are permanent changes chemical structure individual genes and, as a rule, are not reflected in the morphology of chromosomes observed under a microscope. Mutations of genes localized not only in chromosomes, but also in some self-reproducing organelles of the cytoplasm (for example, mitochondria, plastids) are also known.
Causes of mutations and their artificial induction. Polyploidy most often occurs when the chromosomes are separated at the beginning of cell division - mitosis, but for some reason cell division does not occur. Polyploidy can be induced artificially by influencing a cell that has entered mitosis with substances that disrupt cytotomy. Less commonly, polyploidy occurs as a result of the fusion of 2 somatic cells or the participation of 2 sperm in the fertilization of an egg. Haploidy - for the most part a consequence of the development of the embryo without fertilization. It is caused artificially by pollinating plants with dead pollen or pollen of another species (distant). The main cause of aneuploidy is the random nondisjunction of a pair of homologous chromosomes during meiosis, as a result of which both chromosomes of this pair end up in one sex cell or none of them hits it. Less commonly, aneuploids arise from the few viable germ cells formed by unbalanced polyploids.
Causes of chromosomal rearrangements and the most important category mutations - gene mutations - remained unknown for a long time. This gave rise to erroneous autogenetic concepts, according to which spontaneous gene mutations arise in nature, supposedly without the participation of environmental influences. Only after the development of methods for quantitatively recording gene mutations, it became clear that they could be caused by various physical and chemical factors— mutagens.
Recombination
Recombination is the redistribution of genetic material of parents in offspring, leading to hereditary combinative variability in living organisms. In the case of unlinked genes (lying on different chromosomes), this redistribution can be carried out by freely combining chromosomes in meiosis, and in the case of linked genes, usually by crossing chromosomes - crossing over. Recombination is a universal biological mechanism characteristic of all living systems - from viruses to higher plants, animals and humans. At the same time, depending on the level of organization of a living system, the process of recombination (genetic) has a number of features. Recombination occurs most simply in viruses: when a cell is jointly infected with related viruses that differ in one or more characteristics, after cell lysis, not only the original viral particles are detected, but also recombinant particles with new gene combinations appearing at a certain average frequency. In bacteria, there are several processes that end in recombination: conjugation, i.e., the union of two bacterial cells by a protoplasmic bridge and the transfer of a chromosome from a donor cell to a recipient cell, after which individual sections of the recipient chromosome are replaced with corresponding donor fragments; transformation - the transfer of characteristics by DNA molecules penetrating from the environment through cell membrane; transduction is the transfer of genetic substance from a donor bacterium to a recipient bacterium, carried out by a bacteriophage. In higher organisms, recombination occurs in meiosis during the formation of gametes: homologous chromosomes come together and are positioned side by side with great precision (the so-called synapsis), then chromosomes break at strictly homologous points and reunite the fragments crosswise (crossing over). The result of recombination is detected by new combinations of characteristics in the offspring. The probability of crossing over between two chromosome points is approximately proportional to physical distance between these points. This makes it possible, based on experimental data on recombination, to build genetic maps of chromosomes, i.e., graphically arrange genes in linear order in accordance with their location in the chromosomes, and, moreover, on a certain scale. Molecular mechanism recombination has not been studied in detail, but it has been established that enzymatic systems that ensure recombination also take part in such an important process as the correction of damage that occurs in the genetic material. After synapsis, endonuclease, an enzyme that carries out primary breaks in DNA strands, comes into action. Apparently, these breaks in many organisms occur in structurally determined areas - recombinators. Next, double or single strands of DNA are exchanged and, finally, special synthetic enzymes - DNA polymerases - fill the gaps in the strands, and the ligase enzyme closes the last covalent bonds. These enzymes have been isolated and studied only in some bacteria, which has allowed us to get closer to creating a model of recombination in vitro (in vitro). One of the most important consequences of recombination is the formation of reciprocal offspring (i.e., in the presence of two allelic forms of the genes AB and aw, two recombination products should be obtained - aB and aB in equal quantities). The principle of reciprocity is observed when recombination occurs between sufficiently distant points on the chromosome. During intragenic recombination, this rule is often violated. The latter phenomenon, studied mainly in lower fungi, is called gene conversion. The evolutionary significance of recombination lies in the fact that it is often not individual mutations that are beneficial for the organism, but their combinations. However, the simultaneous occurrence of a favorable combination of two mutations in one cell is unlikely. As a result of recombination, mutations belonging to two independent organisms are combined, thereby accelerating the evolutionary process.
Mechanisms of evolution
Natural selection
There are two main evolutionary mechanisms. The first is natural selection, that is, the process by which hereditary traits favorable for survival and reproduction spread throughout the population, while unfavorable ones become rarer. This occurs because individuals with favorable traits are more likely to reproduce, so more individuals in the next generation have the same traits. Adaptations to the environment arise as a result of the accumulation of successive, small, random changes and the natural selection of the variant most adapted to the environment.
Genetic drift
The second main mechanism is genetic drift, an independent process of random variation in the frequency of traits. Genetic drift occurs as a result of probabilistic processes that cause random changes in the frequency of traits in a population. Although changes due to drift and selection within a single generation are quite small, differences in frequencies accumulate in each successive generation and lead to significant changes in living organisms over time. This process may culminate in the formation of a new species. Moreover, the biochemical unity of life indicates the origin of all known species from a common ancestor (or gene pool) through a process of gradual divergence.
There are three main directions of evolution - aromorphosis, idioadaptation and general degeneration. All of them lead to biological progress, i.e., the prosperity of species and larger taxa, when a group increases its numbers and species diversity, and expands its range.
Biological progress is contrasted with biological regression, when the number, range of a species(s), as well as the number of species of a taxon decrease due to the inability of the group to adapt to changing environmental conditions. In other words, biological regression occurs when the historical development of a taxon does not follow any of the directions of evolution.
Aromorphosis
Aromorphosis refers to major evolutionary transformations, usually leading to the emergence of large taxa, for example, classes in animals. Aromorphoses increase general level organizations, making it more complex, are the main path of evolution. They occur rarely, significantly change the morphophysiology of organisms, and allow them to colonize new habitats.
Aromorphosis is complex and affects different organ systems. So the appearance of the lungs “pulled” the appearance of a three-chambered heart. The emergence of a four-chambered heart and the complete separation of blood circulation played a role important role in the appearance of warm-bloodedness.
Examples of aromorphoses: the appearance of photosynthesis, multicellularity, sexual reproduction, the internal skeleton, the development of the lungs, the appearance of warm-bloodedness in animals, the formation of roots and conducting tissues in plants, the appearance of flowers and fruits.
The appearance of lungs allowed organisms to reach land, that is, to populate a habitat with new environmental conditions. The warm-blooded nature that arose in birds and mammals gave them the opportunity to be less dependent on temperature and to inhabit habitats inaccessible to amphibians and reptiles.
Thanks to the appearance of roots that anchor the plant in the soil and absorb water, as well as a conductive system that delivers water to all cells, plants were able to grow on land. Their biomass has reached enormous levels here.
Idiomatic adaptation
Idioadaptation is a small evolutionary change, allowing the species to adapt to specific features habitat and narrow ecological niche. These are private adaptations that do not change the overall level of the organization.
Idioadaptation ensures the emergence of various adaptive forms within one level of organization.
So all mammals have similarities internal structure. However, the diversity of species adapted to different habitats and feeding methods was achieved through such a direction of evolution as idioadaptation.
Angiosperms have many different species, a number of life forms (grasses, shrubs, trees). They are very different in appearance, but their morphology and physiology have the same level of organization.
As a result of idioadaptations, characters that are insignificant for a large taxon change. For example, all birds have a beak; its appearance was ensured by aromorphosis. But each species has its own beak shape and size, adapted to specific feeding methods. This was provided by idioadaptations.
General degeneration
An example of degeneration in the plant world is the dodder, which does not have its own chlorophyll and feeds on other angiosperms.
Apparently, general degeneration in importance should be placed on par with aromorphosis, and not idioadaptation, since it usually affects significant changes in the body. For example, loss the whole system or even organ systems is a major change.
Minor private degenerations leading to a simplification of the structure of an organ, for example, loss good vision in animals leading an underground lifestyle should be considered as an idioadaptation.