What is the significance of the study of phylogenetic series. What is the significance of the reconstruction of phylogenetic series: modern phylogenetics
The methods of phylogenetic research are organically linked with the methods of studying the facts of evolution. Until now, the morphological method must be considered the main method of phylogenetic research, since transformations of the form of an organism remain the most obvious fact and make it possible to trace the phenomena of transformation of species with a great degree of success.
It does not follow from this, of course, that other methods - physiological, ecological, genetic, etc. - are not applicable to phylogenetic studies. The form and function of an organism are inextricably linked. Any organism is formed under the influence of specific environmental factors, it interacts with it, it is in certain relationships with other organisms. However, the form of an organism, its structure, always remains a sensitive indicator of all these connections and serves as a guiding thread for the researcher of phylogenetic questions. The morphological method of research occupies a leading position in the study of phylogeny, and its conclusions have generally been confirmed when they were verified by other methods. The great advantage of the morphological method is the availability of its combination with the comparative method of research, without which it is impossible to detect the very fact of the transformation of living systems. The validity of the morphological method is greatly enhanced by the fact that it is essentially deeply self-critical, since it can be applied in various directions.
If we have a large paleontological material at our disposal (for example, the evolution of a horse), we can apply the comparative morphological method to the successive series of ancestors and descendants and thus identify the directions and methods of evolution of a given group. The figure gives an idea of the essence of the comparative morphological method as applied to the ancestors of the horse. The successive reduction of the lateral fingers and the development of the middle (III) finger show the direction of the evolutionary development of the "horse series".
Comparison of the limbs of jerboas with a decreasing number of fingers and increasing specialization. 1 - small jerboa Allactaga elator, 2 - Salpingotas Koslovi, 3 - upland Dipus sagitta. I-V - fingers from the first to the fifth (According to Vinogradov)
Further, paleontological data are in harmony with comparative anatomical studies of modern forms. The figure compares the limbs of three forms with a decreasing number of fingers. Although this is not a phylogenetic series, the idea is nevertheless created that all three limbs are the result of the manifestation of similar processes that have reached different stages of development. Therefore, the comparative morphological method and in relation to modern forms, regardless of paleontology, makes it possible to assume that, for example, the one-toed foot must have developed from the polydactyl. When the facts of comparative embryology are added to these conclusions, showing that, for example, in the horse embryo, the lateral fingers are laid, and then they are gradually reduced, then our conclusion about the origin of the one-toed horse from the polydactyl ancestor becomes even more probable.
The coincidence of these data shows that the facts of paleontology, comparative anatomy of adult forms and comparative embryology mutually control and complement each other, forming in their totality a synthetic triple method of phylogenetic studies proposed by Haeckel (1899) and which has not lost its significance even now. It is accepted that the coincidence of the data of paleontology, comparative anatomy and embryology, to a certain extent, serves as proof of the correctness of phylogenetic constructions.
These are the most general principles of phylogenetic research.
Let us now consider the briefly described elements of the unified method of phylogenetic studies.
Paleontological evidence is the most convincing. However, they have a major defect, namely, the paleontologist deals only with morphological features and, moreover, incomplete ones. The organism as a whole is beyond paleontological research. In view of this, it is especially important for a paleontologist to take into account all the signs of animals available to him, with the remains of which he is dealing. Otherwise, his phylogenetic conclusions may be erroneous.
Let us assume that the forms A, B, C, D, E, E replace each other in successive geological horizons, and that the paleontologist has the opportunity to observe a certain sum of their features - a, b, c, etc. Let us further assume that the form A has features a 1, b 1, c 1, and in forms B, C, D, ... these signs are changed (respectively a 2, b 2, c 2 .. a 3, b 3, c 3 ..., it. d .). Then in time we get such a series of data
This tablet corresponds, for example, to the "series" of equine ancestors, where from the eopippus to the horse we have a successive change in the development of a number of characters. The table shows the successive development for all leading features. Each subsequent feature (for example, a 4) is derived from each previous one (for example, a 3). In such cases, it becomes probable that the series A, B, C, D, E, E forms phylogenetic series, i.e., a series of ancestors and their descendants. Such is the series from Eogippus to the horse, and some others.
Suppose now that we are dealing with the following data,
i.e., we state a number of forms that successively replace each other in time, and according to one of the signs (b) we get a picture of sequential development from b 1 to b 5. Nevertheless, our series is not a phylogenetic series, since, for example, with respect to characters a and b, we do not observe consistent specialization. For example, type A has the formula A (a 1, b 1, b 1), but type B is clearly not its direct descendant, since it has the formula B (a 4, b 2, b 2), etc. Obviously, we are dealing here with successive "fragments" of a phylogenetic tree, many branches of which have not been found. Therefore, the series A, B, C, D, D, E is actually A, B 1, C 2, G 3, D 1. Such a series is called stepped. To clarify the differences between it and the phylogenetic series, we will use a figure showing the evolution of the horse. Here the following series will be phylogenetic: eogippus, orogippus, mesogippus, paragippus, merigippus, pliogippus, plesippus, horse. For example, the following series of forms would be stepped: hyracotherium, epigippus, myohippus, anchiterium, hipparion, hippidium, horse. All these are not ancestors and descendants, but successive, but scattered lateral branches of the phylogenetic tree.
As you can see, the step row is of great operational importance, since, based on it, one could conclude that the horse descended from a polydactyl ancestor.
Finally, you may encounter adaptive range, showing the development of any adaptation. Such a series may be part of a phylogenetic series, for example, the adaptation of a horse's foot to running, but often this is not the case, and an adaptive series can be compiled even at the expense of modern forms that do not form a phylogenetic series at all. As you can see, the paleontologist has to face great difficulties. His material is fragmentary, not complete.
Some compensation for the incompleteness of paleontological data, however, is the possibility of extending ecological data to paleontology. A certain form of an organ (the structure of the leg, the structure of the dental apparatus, etc.) allows one to draw conclusions about the lifestyle and even about the composition of the food of extinct animals. This gives rise to the possibility of reconstructing their ecological relations. The corresponding field of knowledge laid down in the works of V. O. Kovalevsky was called paleobiology (Abel, 1912). It compensates for the fragmentary nature of the paleontologist's ideas about extinct animals. With regard to forms devoid of a skeleton, paleontology provides only insignificant material on phylogenetics, and in these cases comparative morphology comes first with its method of comparative study of the homologous structures of adult and embryonic forms of geological modernity. The lack of paleontological data makes drawing phylogenetic inferences much more difficult. Therefore, our phylogenetic constructions are most reliable for those forms for which paleontological material is known.
Nevertheless, the researcher does not remain unarmed even in the absence of paleontological data. In this case, he uses a different method, namely, the study of the stages of ontogenetic development.
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One of the most famous and most studied of them is the phylogenetic series of modern ungulates. Multiple paleontological finds and identified transitional forms create a scientific evidence base for this series. Described by the Russian biologist Vladimir Onufrievich Kovalevsky back in 1873, the phylogenetic series of the horse remains today an “icon” of evolutionary paleontology.
Evolution through the ages
In evolution, phylogenetic series are transitional forms that successively replaced each other, leading to the formation of modern species. By the number of links, the series can be complete or partial, however, the presence of successive transitional forms is a prerequisite for their description.
The phylogenetic series of the horse is referred to as evidence of evolution precisely because of the presence of such successive forms that replace each other. The multiplicity of paleontological finds endows it with a high degree of reliability.
Examples of phylogenetic series
The number of horses is not the only one among the examples described. The phylogenetic series of whales and birds is well studied and has a high degree of reliability. And controversial in scientific circles and most used in various populist insinuations is the phylogenetic series of modern chimpanzees and humans. Disputes about the intermediate links missing here do not subside in the scientific community. But no matter how many points of view there are, the significance of phylogenetic series as evidence of the evolutionary adaptability of organisms to changing environmental conditions remains indisputable.
Linking horse evolution to the environment
Multiple studies of paleontologists have confirmed the theory of O. V. Kovalevsky about the close relationship between changes in the skeleton of the ancestors of horses and changes in the environment. The changing climate led to a decrease in forest areas, and the ancestors of modern single-toed ungulates adapted to living conditions in the steppes. The need for rapid movement provoked modifications in the structure and number of fingers on the limbs, changes in the skeleton and teeth.
First link in the chain
In the early Eocene, more than 65 million years ago, the first great ancestor of the modern horse lived. This is a “low horse” or Eohippus, which was the size of a dog (up to 30 cm), relied on the entire foot of the limb, on which there were four (front) and three (rear) fingers with small hooves. Eohippus fed on shoots and leaves and had tuberculate teeth. Brown coloring and sparse hair on a mobile tail - such is the distant ancestor of horses and zebras on Earth.
Intermediates
About 25 million years ago, the climate on the planet changed, and steppe expanses began to replace forests. In the Miocene (20 million years ago), mesogippus and parahippus appear, already more similar to modern horses. And the first herbivorous ancestor in the phylogenetic series of the horse is considered to be merikgippus and pliogippus, which enter the arena of life 2 million years ago. Hipparion - the last three-toed link
This ancestor lived in the Miocene and Pliocene on the plains of North America, Asia and Africa. This three-toed horse, resembling a gazelle, did not yet have hooves, but could run fast, ate grass, and it was she who occupied vast territories.
One-toed horse - pliogippus
These one-toed representatives appear 5 million years ago in the same territories as the hipparions. Environmental conditions are changing - they are becoming even drier, and the steppes are growing significantly. This is where single-fingeredness turned out to be a more important sign for survival. These horses were up to 1.2 meters high at the withers, had 19 pairs of ribs and strong leg muscles. Their teeth acquire long crowns and folds of enamel with a developed cement layer.
The familiar horse
The modern horse as the final stage of the phylogenetic series appeared at the end of the Neogene, and at the end of the last ice age (about 10 thousand years ago) millions of wild horses were already grazing in Europe and Asia. Although the efforts of primitive hunters and the reduction of pastures made a wild horse a rarity already 4 thousand years ago. But its two subspecies - the tarpan in Russia and the Przewalski's horse in Mongolia - managed to hold out much longer than all the others.
wild horses
Today, there are practically no real wild horses left. The Russian tarpan is considered an extinct species, and the Przewalski's horse does not occur naturally. Herds of horses that graze freely are feral domesticated forms. Such horses, although quickly returning to wild life, are still different from truly wild horses.
They have long manes and tails and are variegated. The exceptionally tan horses of Przewalski and the mouse tarpans have, as it were, trimmed bangs, manes and tails.
In Central and North America, wild horses were completely exterminated by the Indians and appeared there only after the arrival of Europeans in the 15th century. The feral descendants of the horses of the conquistadors gave rise to numerous herds of mustangs, the number of which is now controlled by shooting.
In addition to mustangs, there are two types of wild island ponies in North America - on the islands of Assateague and Sable. Semi-wild herds of Camargue horses are found in the south of France. In the mountains and swamps of Britain, you can also find some wild ponies.
Our favorite horses
Man tamed the horse and brought out more than 300 of its breeds. From heavyweights to miniature ponies and handsome race breeds. About 50 breeds of horses are bred in Russia. The most famous of them is the Oryol trotter. Exceptionally white color, excellent trot and agility - these qualities were so appreciated by Count Orlov, who is considered the founder of this breed.
Question 1. What is the difference between macro- and microevolution?
By microevolution we mean the formation of new species.
The concept of macroevolution denotes the origin of supraspecific taxa (genus, order, clan, type).
Nevertheless, there are no fundamental differences between the processes of formation of new species and the processes of formation of higher taxonomic groups. The term "microevolution" in the modern sense was introduced by N. V. Timofeev-Resovsky in 1938.
Question 2. What processes are the driving forces of macroevolution? Give examples of macroevolutionary changes.
In macroevolution, the same processes operate as in speciation: the formation of phenotypic changes, the struggle for existence, natural selection, the extinction of the least adapted forms.
The result of macroevolutionary processes is significant changes in the external structure and physiology of organisms, such as, for example, the formation of a closed circulatory system in animals or the appearance of stomata and epithelial cells in plants. Fundamental evolutionary acquisitions of this kind include the formation of inflorescences or the transformation of the forelimbs of reptiles into wings and a number of others.
Question 3. What facts underlie the study and evidence of macroevolution?
The most compelling evidence for macroevolutionary processes comes from paleontological data. Paleontology studies the fossil remains of extinct organisms and establishes their similarities and differences with modern organisms. From the remains, paleontologists reconstruct the appearance of extinct organisms, learn about the flora and fauna of the past. Unfortunately, the study of fossil forms gives us an incomplete picture of the evolution of flora and fauna. Most of the remains consist of solid parts of organisms: bones, shells, external supporting tissues of plants. Of great interest are fossils that have preserved traces of burrows and passages of ancient animals, prints of limbs or whole organisms left on once soft deposits.
Question 4. What is the significance of the study of phylogenetic series?material from the site
The study of phylogenetic series built on the basis of data from paleontology, comparative anatomy and embryology is important for the further development of the general theory of evolution, the construction of a natural system of organisms, and the reconstruction of a picture of the evolution of a specific systematic group of organisms.
Currently, to build phylogenetic series, scientists are increasingly using data from such sciences as genetics, biochemistry, molecular biology, biogeography, ethology, etc.
