Embryonic evidence. Embryological, paleontological and morphological evidence of the evolution of the organic world. III. Introduction to the topic
The doctrine of evolution causes a lot of controversy. Some believe that God created the world. Others argue with them, saying Darwin was right. They cite numerous paleontological studies that most convincingly support his theory.
The remains of animals and plants, as a rule, decompose and then disappear without a trace. However, sometimes minerals replace biological tissues, resulting in the formation of fossils. Scientists usually discover fossilized shells or bones, that is, skeletons, the hard parts of organisms. Sometimes they find traces of animal activity or prints of their tracks. It's even rarer to spot entire animals. They are found in permafrost ice, as well as in amber (ancient plant resin) or asphalt (a natural resin).
Science paleontology
Paleontology is the science that studies fossil remains. Sedimentary rocks usually occur in layers, which is why the deep layers contain information about the past of our planet. Scientists are able to determine the relative age of certain fossils, that is, understand which organisms lived on our planet earlier and which later. This allows us to draw conclusions about the directions of evolution.
Fossil record
If we look at the fossil record, we will see that life on the planet has changed significantly, sometimes beyond recognition. The first simple unicellular organisms (prokaryotes), which did not have a cell nucleus, arose on Earth approximately 3.5 billion years ago. About 1.75 billion years ago, single-celled eukaryotes appeared. A billion years later, about 635 million years ago, multicellular animals appeared, the first of which were sponges. After another few tens of millions of years, the first mollusks and worms were discovered. 15 million years later, primitive vertebrates appeared, resembling modern lampreys. Gnatched fishes arose about 410 million years ago, and insects appeared about 400 million years ago.
Over the next 100 million years, mostly ferns covered the land, which was inhabited by amphibians and insects. From 230 to 65 million years ago, dinosaurs dominated our planet, and the most common plants at that time were cycads, as well as other groups of gymnosperms. The closer to our time, the more similarities are observed between fossil fauna and flora with modern ones. This picture confirms evolutionary theory. It has no other scientific explanation.
There are various paleontological evidence for evolution. One of them is an increase in the lifespan of families and clans.
Increasing the duration of existence of families and genera
According to available data, more than 99% of all species of living organisms that have ever lived on the planet are extinct species that have not survived to our time. Scientists have described about 250 thousand fossil species, each of which is found exclusively in one or more adjacent layers. Judging by the data obtained by paleontologists, each of them existed for about 2-3 million years, but some were much longer or much less.
The number of fossil genera described by scientists is about 60 thousand, and families - 7 thousand. Each family and each genus, in turn, has a strictly defined distribution. Scientists have found that births live for tens of millions of years. As for families, the duration of their existence is estimated at tens or even hundreds of millions of years.
Analysis of paleontological data shows that over the past 550 million years, the duration of the existence of families and genera has steadily increased. This fact can perfectly explain the gradual accumulation of the most “hardy”, stable groups of organisms in the biosphere. They die out less often because they tolerate environmental changes better.
There are other proofs of evolution (paleontological). By tracing the distribution of organisms, scientists obtained very interesting data.
Distribution of organisms
The distribution of individual groups of living organisms, as well as all of them taken together, also confirms evolution. Only the teachings of Charles Darwin can explain their spread across the planet. For example, “evolutionary series” are found in almost any group of fossils. This is the name given to gradual changes observed in the structure of organisms, which gradually replace each other. These changes often appear to be directional; in some cases we can speak of more or less random fluctuations.
Presence of intermediate forms
Numerous paleontological evidence of evolution includes the existence of intermediate (transitional) forms of organisms. Such organisms combine the characteristics of different species or genera, families, etc. When talking about transitional forms, as a rule, they mean fossil species. However, this does not mean that intermediate species must necessarily become extinct. The theory of evolution, based on the construction of a phylogenetic tree, predicts which of the transitional forms actually existed (and therefore can be discovered) and which did not.
Many such predictions have now come true. For example, knowing the structure of birds and reptiles, scientists can determine the characteristics of the intermediate form between them. It is possible to discover the remains of animals that are similar to reptiles, but have wings; or similar to birds, but with long tails or teeth. It can be predicted that transitional forms between mammals and birds will not be discovered. For example, there have never been mammals that had feathers; or bird-like organisms that have middle ear bones (this is typical for mammals).
Discovery of Archeopteryx
Paleontological evidence of evolution includes many interesting finds. The first skeleton of a representative of the species Archeopteryx was discovered shortly after the publication of the work of Charles Darwin. This work contains theoretical evidence of the evolution of animals and plants. Archeopteryx is a form intermediate between reptiles and birds. His plumage was developed, which is typical for birds. However, in terms of skeletal structure, this animal was practically no different from dinosaurs. Archeopteryx had a long bony tail, teeth, and claws on its forelimbs. As for the skeletal features characteristic of birds, he did not have many of them (fork, hook-shaped processes on the ribs). Later, scientists found other forms intermediate between reptiles and birds.
Discovery of the first human skeleton
Paleontological evidence of evolution also includes the discovery of the first human skeleton in 1856. This event occurred 3 years before the publication of On the Origin of Species. At the time the book was published, scientists knew of no other fossil species that could confirm that chimpanzees and humans descended from a common ancestor. Since then, paleontologists have discovered a large number of skeletons of organisms that are transitional forms between chimpanzees and humans. This is important paleontological evidence for evolution. Examples of some of them will be given below.
Transitional forms between chimpanzees and humans
Charles Darwin (his portrait is shown above), unfortunately, did not learn about the many finds discovered after his death. He would probably be interested to know that this evidence of the evolution of the organic world supported his theory. According to it, as is known, we all descended from monkeys. Since the common ancestor of chimpanzees and humans walked on four limbs, and its brain size was no larger than that of a chimpanzee, in the process of evolution, according to the theory, upright walking should have developed over time. In addition, the brain volume should have increased. Thus, any of three variants of the transitional form must have existed:
- large brain, undeveloped upright posture;
- developed upright posture, brain size like that of a chimpanzee;
- developing upright posture, brain volume is intermediate.
Australopithecus remains
In Africa in the 1920s. The remains of an organism were found that was named Australopithecus. This name was given to it by Raymond Dart. This is further proof of evolution. Biology has accumulated information about many similar finds. Scientists later discovered other remains of such creatures, including the skull of AL 444-2 and the famous Lucy (pictured above).
Australopithecus lived in northern and eastern Africa between 4 and 2 million years ago. They had a slightly larger brain than chimpanzees. The structure of their pelvic bones was close to human ones. The structure of the skull is characteristic of upright animals. This can be determined by the hole in the occipital bone, which connects the cranial cavity to the spinal canal. Moreover, “human” traces were found in volcanic fossilized ash in Tanzania, which were left approximately 3.6 million years ago. Australopithecines are thus an intermediate form of the second of the above types. Their brain is approximately the same as that of a chimpanzee, and they have a developed upright posture.
Remains of Ardipithecus
Later, scientists discovered new paleontological finds. One of them is the remains of Ardipithecus, who lived about 4.5 million years ago. After analyzing its skeleton, they found out that Ardipithecus walked on the ground on two hind limbs, and also climbed trees on all four. They had a poorly developed upright posture compared to subsequent hominid species (australopithecines and humans). Ardipithecus could not move over significant distances. They are a transitional form between the common ancestor of chimpanzees and humans and Australopithecus.
Numerous pieces of evidence were found. We have only talked about some of them. Based on the information received, scientists have formed an idea of how hominids have changed over time.
Hominid evolution
It should be noted that many people are still not convinced by the evidence of evolution. The table with information about human origins, which is presented in every school biology textbook, haunts people, causing numerous disputes. Can this information be included in the school curriculum? Should children study evidence of evolution? The table, which is for informational purposes only, outrages those who believe that man was created by God. One way or another, we will present information about the evolution of hominids. And you decide how to treat her.
In the course of evolution, hominids first developed an upright posture, and the volume of their brains was significantly increased much later. In Australopithecines, who lived 4-2 million years ago, it was approximately 400 cm³, almost like that of chimpanzees. After them, the species inhabited our planet. Its bones, whose age is estimated at 2 million years, were discovered, and more ancient stone tools were found. About 500-640 cm³ was the size of his brain. Further in the course of evolution, the Working Man arose. His brain was even larger. Its volume was 700-850 cm³. The next species, Homo erectus, was even more similar to modern humans. The volume of his brain is estimated to be 850-1100 cm³. Then a species appeared. Its brain size had already reached 1100-1400 cm³. Next came the Neanderthals, who had a brain with a volume of 1200-1900 cm³. Homo sapiens arose 200 thousand years ago. It is characterized by a brain size of 1000-1850 cm³.
So, we have presented the main evidence for the evolution of the organic world. How you treat this information is up to you. The study of evolution continues to this day. It is likely that new interesting discoveries will be discovered in the future. Indeed, the science of paleontology is currently actively developing. The evidence of evolution that it provides is actively discussed by both scientists and non-scientific people.
Scientific evidence of evolution (embryological, morphological, paleontological, biogeographical, etc.)
Embryological evidence
In all vertebrates, there is a significant similarity of embryos in the early stages of development: they have a similar body shape, there are rudiments of gill arches, there is a tail, one circle of blood circulation, etc. However, as development progresses, the similarity between the embryos of different systematic groups gradually decreases, and they begin to predominate features characteristic of their classes, orders, families, genera, and, finally, species.
Evolutionary changes can affect all phases of ontogenesis, that is, they can lead to changes not only in mature organisms, but also in embryos, even in the first stages of development. However, earlier phases of development should be more conservative than later ones, since changes at earlier stages of development should in turn lead to greater changes during later development. For example, a change in the type of cleavage will cause changes in the process of gastrulation, as well as in all subsequent stages. Therefore, changes that appear in the early stages are much more likely to be lethal than changes that occur in later periods of ontogenesis.
Thus, the early stages of development change relatively rarely, which means that by studying embryos of different species, it is possible to draw conclusions about the degree of evolutionary relatedness.
In 1837, embryologist Karl Reichert discovered from which embryonic structures the quadrate and articular bones in the jaw of reptiles develop. The same structures are found in mammalian embryos, but they develop into the malleus and incus of the middle ear. The fossil record also confirms the origin of parts of the mammalian ear from the jaw bones reptiles.
There are many other examples of how the evolutionary history of an organism is revealed during its development. Mammalian embryos at early stages have gill sacs, indistinguishable in structure from the gill sacs of aquatic vertebrates. This is explained by the fact that the ancestors of mammals lived in water and breathed with gills. Of course, the gill pouches of mammalian embryos do not develop into gills during development, but into structures that evolved from gill slits or the walls of gill pouches, such as the eustachian tubes, middle ear, tonsils, parathyroid glands and thymus.
The embryos of many species of snakes and legless lizards (for example, the brittle spindle) develop the rudiments of limbs, but then they are resorbed. Similarly, whales, dolphins and porpoises do not have hind limbs, but cetacean embryos begin to grow hind legs, develop bones, nerves, blood vessels, and then all these tissues are resorbed.
Darwin cited the presence of teeth in the embryos of baleen whales as an example.
Biogeographical evidence
Among Australia's mammals, marsupials predominate. Placental mammals include cetaceans, pinnipeds and bats (which could have moved to Australia relatively easily), as well as rodents, which appear in the fossil record in the Miocene, when Australia approached New Guinea. At the same time, the natural conditions of Australia are favorable for other species of mammals. For example, rabbits introduced to the continent quickly multiplied, spread widely and continue to displace native species. In Australia and New Guinea, in the south of South America and Africa, flightless ratites, whistlers (toothed toads) and lungfishes are found; in other parts of the world they are absent. Living conditions in the deserts of Africa, America and Australia are very similar, and plants from one desert grow well in another. However, cacti have only been found in America (with the exception of Rhipsalis baccifera, apparently brought to the Old World by migratory birds). Many African and Australian succulents (that is, plants with special tissues for storing water) superficially resemble cacti due to convergent evolution, but belong to different orders. The marine life of the eastern and western coasts of South America is different, with the exception of some mollusks, crustaceans and echinoderms, but about 30% of the same fish species live on opposite shores of the Isthmus of Panama, which is explained by the recent emergence of the isthmus (about 3 million years ago). Most oceanic islands (that is, islands that have never been connected to the mainland) lack land mammals, amphibians and other animals that are unable to overcome significant water obstacles. The species composition of the fauna of such islands is poor and is the result of the accidental introduction of some species, usually birds, reptiles, and insects.
The geographical distribution of species in the past, which can be partially reconstructed from fossil remains, must also correspond to the phylogenetic tree. The theory of continental drift and the theory of evolution make it possible to predict where certain fossil remains should be found. The first fossils of marsupials were found in North America, their age is about 80 million years. 40 million years ago, marsupials were already common in South America, but in Australia, where they now dominate, marsupials appeared only about 30 million years ago. Evolutionary theory predicts that Australian marsupials are descended from American marsupials. According to the theory of continental drift, 30-40 million years ago, South America and Australia were still part of Gondwana, a large continent in the southern hemisphere, and between them was the future Antarctica. Based on two theories, researchers predicted that marsupials migrated from South America to Australia via Antarctica 30-40 million years ago. This prediction came true: since 1982, more than ten fossil marsupials aged 35-40 million years have been found on Seymour Island, located near Antarctica.
The closest relatives of modern humans - gorillas and chimpanzees - live in Africa. Based on this, in 1872 Charles Darwin suggested that the ancient ancestors of man should be sought in Africa. Many researchers, such as Louis, Mary and Richard Leakey, Raymond Dart and Robert Broome, followed Darwin's advice, and starting in the 1920s, many intermediate forms between humans and apes were found in Africa. If fossil australopithecines had been discovered, for example, in Australia, and not in Africa, then ideas about the evolution of hominids would have to be revised.
Morphological evidence
In the course of evolution, each new organism is not designed from scratch, but is derived from an old one through a sequence of small changes. The structures formed in this way have a number of characteristic features that indicate their evolutionary origin. Comparative anatomical studies make it possible to identify such features.
In particular, evolutionary origin excludes the possibility of purposefully borrowing successful designs from other organisms. Therefore, different, not closely related species use different organs to solve similar problems. For example, the wing of a butterfly and the wing of a bird develop from different germ layers, the wings of birds are modified forelimbs, and the wings of a butterfly are folds of chitinous cover. The similarity between these organs is superficial and is a consequence of their convergent origin. Such organs are called analogous.
The opposite situation is observed in closely related species: organs with similar structures are used for completely different tasks. For example, the forelimbs of vertebrates perform a variety of functions, but at the same time they have a common structural plan, occupy a similar position and develop from the same rudiments, that is, they are homologous. The similarity in the structure of a bat's wing and a mole's paw cannot be explained in terms of utility. At the same time, the theory of evolution provides an explanation: four-legged vertebrates inherited a single limb structure from a common ancestor.
Each species inherits from the ancestral species most of its properties - including sometimes those that are useless for the new species. Changes usually occur due to the gradual sequential transformation of the characteristics of the ancestral species. The similarity of homologous organs, not related to the conditions of their functioning, is evidence of their development during evolution from a common prototype present in the ancestral species. Other examples of evolutionary changes in morphology are rudiments, atavisms, as well as numerous cases of specific imperfections in the structure of organisms.
Homologous organs
Homology (biology)
Five-fingered limb
Using mammals as an example:
In monkeys, the forelimbs are elongated, the hands are adapted for grasping, which makes climbing trees easier.
The pig's first toe is missing, and the second and fifth are reduced. The remaining two fingers are longer and harder than the others, the terminal phalanges are covered with hooves.
The horse also has a hoof instead of claws, the leg is elongated due to the bones of the middle finger, which contributes to high speed of movement.
Moles have shortened and thickened fingers, which help with digging.
The anteater uses its large middle finger to dig out anthills and termite nests.
In whales, the forelimbs are fins. Moreover, the number of phalanges of the fingers is increased compared to other mammals, and the fingers themselves are hidden under soft tissues.
In the bat, the forelimbs are modified into wings by significantly elongating the four digits, and the hook-shaped first digit is used to hang on trees.
Moreover, all these limbs contain a similar set of bones with the same relative arrangement. The unity of structure cannot be explained in terms of utility, since the limbs are used for completely different purposes.
Parts of insect mouthparts
The main parts of the oral apparatus of insects are the upper lip, a pair of mandibles (upper jaws), the subpharynx, two maxillae (lower jaws) and the lower lip (fused second maxillae). These components vary in shape and size in different species, and in many species some of the parts are lost. The structural features of the oral apparatus allow insects to use various food sources (see figure):
In their original form (for example, in a grasshopper), strong mandibles and maxillae are used for biting and chewing.
The honey bee uses its lower lip to collect nectar, and uses its mandibles to crush pollen and knead wax.
In most butterflies, the upper lip is reduced, mandibles are absent, and the maxillae form a proboscis.
In female mosquitoes, the upper lip and maxillae form a tube, and the mandibles are used to pierce the skin.
Similar bodies
Externally similar organs or parts thereof, originating from different initial rudiments and having a different internal structure, are called analogous. External similarity arises in the course of convergent evolution, that is, in the course of independent adaptation to similar conditions of existence.
The wings of birds are modified forelimbs, the wings of insects are folds of chitinous cover.
The gills of fish are formations associated with the internal skeleton, the gills of many crustaceans are outgrowths of the limbs, the ctenidial gills of mollusks develop in the mantle cavity, and the gills of nudibranchs are outgrowths of the integument of the dorsal side of the body.
Streamlined body shape in aquatic mammals - whales, dolphins - and fish.
The spines of barberry and cactus are modified leaves; the spines of hawthorn develop from shoots.
Grape tendrils (formed from shoots) and pea tendrils (modified leaves).
The shape of various succulents (plants that have special tissues to store water), such as cacti and milkweed.
The complete absence of purposeful borrowing of successful designs distinguishes evolution from conscious design. For example, a feather is a good design that helps with flight, but mammals (including bats) do not have feathers. Gills are extremely useful for aquatic animals, but mammals (such as cetaceans) lack them. To falsify the theory of evolution, it is enough to discover feathers or gills in any species of mammals.
Rudiments
Rudiments are organs that have lost their basic significance in the process of evolutionary development of the organism. If a rudiment turns out to be functional, then it performs relatively simple or unimportant functions with the help of structures intended for more complex purposes
For example, a bird's wing is an extremely complex anatomical structure specially adapted for active flight, but ostrich wings are not used for flight. These vestigial wings can be used for relatively simple tasks, such as maintaining balance while running and attracting mates. In comparison, the winged penguin is of great importance, acting as a fin, and therefore cannot be considered a vestigial.
The eyes of some cave and burrowing animals, such as proteus, mole rat, mole, and Astyanax mexicanus, blind cave fish. Often the eyes are hidden under the skin.
Tibia in birds.
Remains of hair and pelvic bones in some cetaceans.
Some snakes, including the python, have hind limb bones. These bones are not attached to the spine and move relatively freely in the abdominal cavity.
In many beetle species, such as Apterocyclus honoluluensis, the wings lie under fused elytra.
In humans, the rudiments include, in particular, the caudal vertebrae, the hair of the body, the ear muscles, the tubercle of the auricle, and the Morganian ventricles of the larynx.
The vermiform appendix of the cecum (appendix) in some herbivores is used to digest plant food and is long. For example, a koala's appendix is 1 to 2 meters long. The human appendix has a length of 2 to 20 centimeters and is not involved in the breakdown of food. Contrary to popular belief, the presence of secondary functions in the appendix does not mean that it is not a vestige.
Atavisms
Atavism is the appearance in an individual of characteristics characteristic of distant ancestors, but absent in nearby ones. The appearance of atavisms is explained by the fact that the genes responsible for this trait are preserved in DNA, but normally do not form structures typical of ancestors.
Examples of atavisms:
Caudal appendage in humans;
Continuous hair on the human body;
Additional pairs of mammary glands;
The hind legs of whales;
The hind fins of dolphins;
Hind legs of snakes;
Extra toes in horses
The arguments for evolution are similar to those for vestiges.
Paleontological evidence
As a rule, the remains of plants and animals decompose and disappear without a trace. But sometimes biological tissues are replaced by minerals, and fossils are formed. Usually found are fossilized bones or shells, that is, solid parts of living organisms. Sometimes prints of animal tracks or traces of their vital activity are found. It is even less common to find an entire animal - frozen into ice in areas of modern permafrost, trapped in the later fossilized resin of ancient plants (amber) or in another natural resin - asphalt.
Paleontology is the study of fossil remains. Typically, sedimentary rocks are deposited in layers, so deeper layers contain fossils from an earlier period (superposition principle). This means that by comparing fossil forms from successive strata, we can draw conclusions about the main directions of the evolution of living organisms. Numerous geochronological techniques are used to estimate the age of fossils.
When looking at the fossil record, we can conclude that life on Earth has changed significantly. The deeper we look into the past, the less we see in common with the modern biosphere. The first prokaryotes (the simplest single-celled organisms that do not have a formed cell nucleus) appear approximately 3.5 billion years ago. The first unicellular eukaryotes appear 2.7-1.75 billion years ago. About a billion years later, 840 million years ago, the first multicellular animals, representatives of the Hainan fauna, appear in the fossil record. According to a study published in 2009, multicellular organisms belonging to one of the modern types, sponges, probably already existed more than 635 million years ago. During the “Cambrian explosion”, 540-530 million years ago, in a geologically short period of time, remains of representatives of most modern types with skeletons appear in the geological record, and after another 15 million years - the first primitive vertebrates, similar to modern lampreys. Jawed fishes appeared 410 million years ago, insects - 400 million years ago, and for another 100 million years ferns dominated on land, and insects and amphibians remained the main groups of terrestrial fauna. From 250 to 65 million years ago on Earth, the dominant position of “top predators” and large herbivores was occupied by dinosaurs and other reptiles; the most common plants were cycads and other groups of gymnosperms. The first fossil remains of flowering plants appear 140-130 million years ago, and the beginning of their widespread distribution dates back to the mid-Cretaceous period (about 100 million years ago). The observed picture corresponds to the origin of all species from single-celled organisms and has no other scientific explanation.
Well-known evidence of evolution is the presence of so-called intermediate forms, that is, organisms that combine the characteristic features of different species. As a rule, when talking about intermediate (or “transitional”) forms, they mean fossil species, although intermediate species do not always go extinct. Based on the phylogenetic tree, the theory of evolution predicts which intermediate forms can be found and which cannot. According to the scientific method, predictions that come true confirm the theory. For example, knowing the structure of the organisms of reptiles and birds, one can predict some features of the transitional form between them. One can predict the possibility of finding the remains of animals similar to reptiles, but with feathers, or the remains of animals similar to birds, but with teeth, or with long tails with a skeleton of unfused vertebrae. It can be predicted that transitional forms between birds and mammals will not be found, for example - fossil mammals with feathers or bird-like fossils with middle ear bones like mammals.
Shortly after the publication of The Origin of Species, the remains of Archeopteryx, an intermediate form between reptiles and birds, were discovered. Archeopteryx is characterized by differentiated plumage (a typical bird feature), and in terms of skeletal structure it differed little from dinosaurs from the group of compsognaths. It had claws on the forelimbs, teeth and a long tail with a skeleton of unfused vertebrae, and the supposed unique "avian" skeletal features were subsequently identified in other reptiles. Later, other transitional forms between reptiles and birds were found.
Many other transitional forms are known, including from invertebrates to fish, from fish to tetrapods, from amphibians to reptiles, and from reptiles to mammals.
In some cases, fossil transitional forms could not be found, for example, there are no traces of the evolution of chimpanzees (presumably due to the lack of conditions for the formation of fossils in the forests where they live), there are no traces of ciliated worms, and this class unites more than 3,500 species. Of course, to falsify the theory of evolution, it is not enough to point out such gaps in the fossil record. To refute the doctrine of evolution, it would be necessary to present a skeleton that does not correspond to the phylogenetic tree or does not fit into the chronological sequence. Thus, in response to a question about what discovery could falsify evolutionary theory, John Haldane snapped: “Fossil rabbits in the Precambrian!” Millions of fossils have been found [about 250,000 fossil species, and each find is a test of the theory of evolution, and the test passed confirms the theory.
In cases where the fossil record turns out to be particularly complete, it becomes possible to construct so-called phylogenetic series, that is, series of species (genera, etc.), successively replacing each other in the process of evolution. The best known are the phylogenetic series of humans and horses (see below), and the evolution of cetaceans can also be cited as an example.
Embryological evidence of evolution
All multicellular animals go through the blastula and gastrula stages during individual development. The similarity of embryonic stages within individual species and classes is particularly clear. For example, in all terrestrial vertebrates, as well as in fish, the formation of gill arches is found, although these formations have no functional significance in adult organisms. This similarity of embryonic embryonic stages is explained by the unity of origin of all living organisms.
Morphological evidence of evolution
The existence of forms combining the characteristics of several systematic units indicates that in previous geological eras there lived organisms that were the ancestors of several systematic groups. Based on Kovalevsky’s research, the entire group of animals was added to the vertebrates and this type was given the name chordate. The connection between different classes of animals also well illustrates their common origin. The structure of the forelimbs of some vertebrates, despite the performance of completely different functions by these organs, is generally similar. Some bones in the skeleton of the limbs may be absent, others may be fused, but their homology is quite obvious. Organs that develop from the same embryonic rudiments in a similar way are called homologous. Some organs do not function in adult animals and are redundant - these are rudiments. The presence of rudiments as well as homologous organs is evidence of a common origin
Paleontological features
Paleontological data indicate a change in animals and plants over time. Paleontology also points to the causes of evolutionary transformations. The richest paleontological material is one of the most convincing evidence of the evolutionary process.
Biogeographic evidence for evolution
A clear indication of the evolutionary changes that have occurred and are ongoing is the distribution of various animals and plants throughout the planet. A. Wallace managed to compile the biogeography of the regions:
1) Palearctic
2) Neoarctic
3) Indo-Malayan
4) Ethiopian
5) Neotropical
6) Australian.
Comparison of the animal and plant worlds between zones provides rich material for evidence of the evolutionary process. The distribution of animal and plant species over the surface of the planet and their grouping into biogeographic zones reflects the process of the historical development of the Earth and the evolution of animals
Island flora and fauna.
To understand the evolutionary process, the fauna and flora of the islands are of interest. The composition of their F and F depends entirely on the origin of these islands. Islands can be of continental origin or oceanic. Mainland islands are characterized by flora and fauna similar in composition to that of the mainland. The older the island and the more significant the water barrier, the more differences are found. When examining oceanic islands, it was found that their species composition is very poor. There are no land mammals or amphibians. The entire fauna of oceanic islands is the result of accidental settlement. A huge number of various factors indicate that the characteristics of the distribution of living beings on the planet are closely related to the transformation of the earth's crust and the evolutionary change of species.
71. Evidence of evolution: comparative anatomical, embryological, paleontological, etc.
Paleontological evidence of evolution. Fossil remains are the basis for restoring the appearance of ancient organisms. The similarity between fossils and modern organisms is proof of their relationship. Conditions for the preservation of fossil remains and imprints of ancient organisms. The distribution of ancient, primitive organisms in the deepest layers of the earth's crust, and highly organized ones in the later layers.
Transitional forms (Archaeopteryx, wild-toothed lizard), their role in establishing connections between systematic groups. Phylogenetic series - series of successively replacing each other (for example, the evolution of a horse or elephant).
2. Comparative anatomical evidence of evolution:
1) cellular structure of organisms. Similarity in the structure of cells of organisms of different kingdoms;
2) general plan of the structure of vertebrate animals - bilateral symmetry of the body, spine, body cavity, nervous, circulatory and other organ systems;
3) homologous organs, a single structure plan, common origin, performance of various functions (skeleton of the forelimb of vertebrates);
4) similar organs, similarity of functions performed, differences in general structure and origin (gills of fish and crayfish). Lack of relationship between organisms with similar organs;
5) rudiments - disappearing organs that, in the process of evolution, have lost their significance for the preservation of the species (the first and third fingers in the wing of birds, the second and fourth fingers of a horse, the pelvic bones of a whale);
6) atavisms - the appearance of signs of ancestors in modern organisms (highly developed hair, multiple nipples in humans).
3. Embryological evidence for evolution:
1) during sexual reproduction, the development of organisms from a fertilized egg;
2) the similarity of the embryos of vertebrate animals in the early stages of their development. Formation of characteristics of a class, order, and then genus and species in embryos as they develop;
3) the biogenetic law of F. Muller and E. Haeckel - each individual in ontogenesis repeats the history of the development of its species (the body shape of the larvae of some insects is evidence of their origin from worm-like ancestors).
72. A.I. Severtsov’s teaching on phylembryogenesis.
PHYLEMBRYOGENESIS- an evolutionary change in the ontogenesis of organs, tissues and cells, associated with both progressive development and reduction. The doctrine of phylembryogenesis was developed by the Russian evolutionary biologist A.N. Severtsov. The modes (methods) of phylembryogenesis differ in the time of occurrence during the development of these structures. If the development of a certain organ in descendants continues after the stage at which it ended in the ancestors, anabolia occurs (from the Greek anabole - rise) - an extension of the final stage of development. An example is the formation of a four-chambered heart in mammals. Amphibians have a three-chambered heart: two atria and one ventricle. In reptiles, a septum develops in the ventricle (first anabolia), but in most of them this septum is incomplete - it only reduces the mixing of arterial and venous blood. In crocodiles and mammals, the development of the septum continues until the complete separation of the right and left ventricles (second anabolia). In children, sometimes, as an atavism, the interventricular septum is underdeveloped, which leads to a serious illness requiring surgical intervention.
Prolonging the development of an organ does not require profound changes in the previous stages of its ontogenesis, therefore anabolism is the most common method of phylembryogenesis. The stages of organ development preceding anabolism remain comparable to the stages of ancestral phylogeny (i.e., they are recapitulations) and can serve for its reconstruction (see Biogenetic Law). If the development of an organ at intermediate stages deviates from the path along which its ontogenesis took place in its ancestors, deviation occurs. For example, in fish and reptiles, scales appear as thickenings of the epidermis and the underlying connective tissue layer of the skin - the corium. Gradually thickening, this anlage bends outward. Then in fish the corium ossifies, the forming bone scales pierce the epidermis and move to the surface of the body. In reptiles, on the contrary, bone is not formed, but the epidermis becomes keratinized, forming the horny scales of lizards and snakes. In crocodiles, the corium can ossify, forming the bony basis of the horny scales. Deviations lead to a more profound restructuring of ontogenesis than anabolism, so they are less common.
Changes in the primary organ rudiments—archallaxis—occur least often. In case of deviation, recapitulation can be traced from the origin of the organ to the moment of developmental deviation. In archallaxis there is no recapitulation. An example is the development of vertebral bodies in amphibians. In fossil amphibians - stegocephalians and in modern tailless amphibians, the vertebral bodies are formed around a chord of several, usually three on each side of the body, separate anlage, which then merge to form the vertebral body. In tailed amphibians these anlages do not appear. Ossification grows above and below, covering the notochord, so that a bone tube is immediately formed, which, thickening, becomes the vertebral body. This archallaxis is the reason for the still debated question of the origin of tailed amphibians. Some scientists believe that they descended directly from lobe-finned fish, regardless of other land vertebrates. Others say that tailed amphibians diverged very early from other amphibians. Still others, neglecting the development of the vertebrae, prove the close relationship of tailed and tailless amphibians.
Organ reduction, which have lost their adaptive significance, also occurs through phylembryogenesis, mainly through negative anabolism - loss of the final stages of development. In this case, the organ either underdevelops and becomes a rudiment, or undergoes reverse development and completely disappears. An example of a rudiment is the human appendix - an underdeveloped cecum; an example of complete disappearance is the tail of frog tadpoles. Throughout its life in water, the tail grows, new vertebrae and muscle segments are added at its end. During metamorphosis, when the tadpole turns into a frog, the tail dissolves, and the process occurs in the reverse order - from the end to the base. Phylembryogenesis is the main method of adaptive changes in the structure of organisms during phylogenesis.
] [ Belarusian language ] [ Russian literature ] [ Belarusian literature ] [ Ukrainian literature ] [ Fundamentals of health ] [ Foreign literature ] [ Natural history ] [ Man, Society, State ] [ Other textbooks ]
§ 17. Evidence of evolution
To substantiate the theory of evolution, Charles Darwin widely used numerous evidence from the fields of paleontology, biogeography, and morphology. Subsequently, facts were obtained that recreated the history of the development of the organic world and served as new evidence of the unity of the origin of living organisms and the variability of species in nature.
Paleontological finds- perhaps the most convincing evidence of the evolutionary process. These include fossils, imprints, fossil remains, fossil transitional forms, phylogenetic series, sequence of fossil forms. Let's take a closer look at some of them.
1. Fossil transitional forms- forms of organisms that combine the characteristics of older and younger groups.
Of particular interest among plants are psilophytes. They originated from algae, were the first of the plants to make the transition to land and gave rise to higher spore and seed plants. Seed ferns- a transitional form between ferns and gymnosperms, and cycads - between gymnosperms and angiosperms.
Among fossil vertebrates, one can distinguish forms that are transitional between all classes of this subtype. For example, the oldest group lobe-finned fish gave rise to the first amphibians - stegocephalus(Fig. 3.15, 3.16). This was possible due to the characteristic structure of the skeleton of the paired fins of lobe-finned fish, which had the anatomical prerequisites for their transformation into the five-fingered limbs of primary amphibians. Forms are known that form the transition between reptiles and mammals. These include beast lizards(foreigner disease) (Fig. 3.17). And the connecting link between reptiles and birds was per-bird(Archaeopteryx) (Fig. 3.18).
The presence of transitional forms proves the existence of phylogenetic connections between modern and extinct organisms and helps in building a natural system and family tree of the flora and fauna.
2. Paleontological series- series of fossil forms related to each other in the process of evolution and reflecting the course of phylogenesis (from the Greek. phylon- clan, tribe, genesis- origin). A classic example of the use of series of fossil forms to elucidate the history of a particular group of animals is the evolution of the horse. Russian scientist V.O. Kovalevsky (1842-1883) showed the gradual evolution of the horse, establishing that successive fossil forms became increasingly similar to modern ones (Fig. 3.20).
Modern one-toed animals descended from small five-toed ancestors who lived in forests 60-70 million years ago. Climate change has led to an increase in the area of steppes and the spread of horses across them. Movement over long distances in search of food and protection from predators contributed to the transformation of the limbs. At the same time, the size of the body and jaws increased, the structure of the teeth became more complex, etc.
To date, a sufficient number of paleontological series are known (proboscis, carnivores, cetaceans, rhinoceroses, some groups of invertebrates), which prove the existence of an evolutionary process and the possibility of the origin of one species from another.
Morphological evidence are based on the principle: the deep internal similarity of organisms can show the relationship of the compared forms, therefore, the greater the similarity, the closer their relationship.
1. Homology of organs. Organs that have a similar structure and common origin are called homologous. They occupy the same position in the animal’s body, develop from similar rudiments and have the same structural plan. A typical example of homology is the limbs of terrestrial vertebrates (Fig. 3.21). Thus, the skeleton of their free forelimbs necessarily has a humerus, a forearm, consisting of the radius and ulna, and a hand (wrist, metacarpus and phalanges of the fingers). The same pattern of homology is observed when comparing the skeleton of the hind limbs. In the horse, the stylus bones are homologous to the metacarpal bones of the second and fourth fingers of other ungulates. It is obvious that in the modern horse these toes have disappeared during the process of evolution.
It has been proven that the poisonous glands of snakes are a homologue of the salivary glands of other animals, the sting of a bee is a homologue of the ovipositor, and the sucking proboscis of butterflies is a homologue of the lower pair of jaws of other insects.
Plants also have homologous organs. For example, pea tendrils, cactus and barberry spines are modified leaves.
Establishing the homology of organs allows us to find the degree of relationship between organisms.
2. Analogy.Similar bodies- these are organs that are externally similar and perform the same functions, but have different origins. These organs indicate only a similar direction of adaptation of organisms, determined in
the process of evolution through the action of natural selection. The external gills of tadpoles, the gills of fish, polychaete annelids, and aquatic insect larvae (such as dragonflies) are similar. Walrus tusks (modified fangs) and elephant tusks (overgrown incisors) are typical analogous organs, since their functions are similar. In plants, barberry spines (modified leaves), white acacia spines (modified stipules) and rose hips (develop from bark cells) are similar.
- Rudiments.Vestigial(from lat. rudimentum- rudiment, primary basis) are organs that are formed during embryonic development, but later stop developing and remain in adult forms in an underdeveloped state. In other words, rudiments are organs that have lost their functions. Rudiments are the most valuable evidence of the historical development of the organic world and the common origin of living forms. For example, anteaters have rudimentary teeth, humans have ear muscles, skin muscles, the third eyelid, and snakes have limbs (Fig. 3.22).
- Atavisms. The appearance in individual organisms of any type of characteristics that existed in distant ancestors, but were lost during evolution, is called atavism(from lat. atavus- ancestor). In humans, atavisms are the tail, hair on the entire surface of the body, and multiple nipples (Fig. 3.23). Among thousands of one-toed horses, there are specimens with three-toed limbs. Atavisms do not carry any functions important for the species, but show the historical relationship between extinct and currently existing related forms.
Embryological proof stva. In the first half of the 19th century. Russian embryologist K.M. Baer (1792-1876) formulated the law of germinal similarity: the earlier stages of individual development are studied, the more similarities are found between different organisms.
For example, in the early stages of development, vertebrate embryos do not differ from each other. Only at the middle stages do features characteristic of fish and amphibians appear, and at later stages do features of the development of reptiles, birds and mammals appear (Fig. 3.24). This pattern in the development of embryos indicates the relationship and sequence of divergences in the evolution of these groups of animals.
The deep connection between the individual and the historical is expressed in biogenetic law, established in the second half of the 19th century. German scientists E. Haeckel (1834-1919) and F. Müller (1821-1897). According to this law, each individual in its individual development (ontogenesis) repeats the history of the development of its species, or ontogenesis is short
and rapid repetition of phylogeny. For example, in all vertebrates, a notochord is formed during ontogenesis, a feature that was characteristic of their distant ancestors. The tadpoles of tailless amphibians develop a tail, which is a repetition of the characteristics of their tailed ancestors.
Subsequently, amendments and additions were made to the biogenetic law. A special contribution to elucidating the connections between onto- and phylogeny was made by the Russian scientist A.N. Severtsov (1866-1936).
It is clear that in such a short period of time as individual development, all stages of evolution cannot be repeated. Therefore, the repetition of the stages of the historical development of a species in embryonic development occurs in a compressed form, with the loss of many stages. At the same time, the embryos of organisms of one species are similar not to the adult forms of another species, but to their embryos. Thus, the gill slits in a one-month-old human embryo are similar to those in a fish embryo, but not in an adult fish. This means that during ontogenesis, mammals go through stages similar to fish embryos, and not to adult fish.
It should be noted that Charles Darwin drew attention to the phenomenon of repetition in ontogenesis of the structural features of ancestral forms.
All of the above information is of great importance for proving evolution and for elucidating related relationships between organisms.
Biogeographic evidence. Biogeography is the science of the patterns of modern settlement of animals and plants on Earth.
You already know from the physical geography course that modern geographic zones were formed during the historical development of the Earth, as a result of the action of climatic and geological factors. You also know that often similar natural zones turn out to be inhabited by different organisms, and different zones are similar. Explanations for these facts can only be found from the standpoint of evolution. For example, the originality of the flora and fauna of Australia is explained by its isolation in the distant past, and therefore the development of the animal and plant world occurred in isolation from other continents. Consequently, biogeography contributes much evidence to the evolution of the organic world.
Currently, methods of biochemistry and molecular biology, genetics, and immunology are widely used to prove evolutionary processes.
Thus, by studying the composition and sequence of nucleotides in nucleic acids and amino acids in proteins in different groups of organisms and detecting similarities, one can judge their relationship.
Biochemistry has research methods that can be used to determine the “blood relationship” of organisms. When comparing blood proteins, the ability of organisms to produce antibodies in response to the introduction of foreign proteins into the blood is taken into account. These antibodies can be isolated from blood serum and determined at what dilution this serum will react with the serum of the comparison organism. This analysis showed that the closest relatives of humans are the great apes, and the most distant of them are lemurs.
The evolution of the organic world on Earth is confirmed by many facts from all areas of biology: paleontology (phylogenetic series, transitional forms), morphology (homology, analogy, rudiments, atavisms), embryology (law of embryonic similarity, biogenetic law), biogeography, etc.
1. What does paleontology study and what paleontological evidence of evolution do you know? 2. How do homologous organs differ from similar ones and what is their significance in proving evolution? 3. Which of the listed organs are homologous and which are similar: gills of fish, crayfish; sepals, petals, stamens, pistil, leaves; barberry spines, pea tendrils, grape tendrils? 4. What do rudiments and atavisms indicate? 5. What is the essence and significance of the law of germinal similarity? 6. Why are marsupials found predominantly in Australia? 7. What methods are currently used to prove the relationship between organisms of different species?
General biology: Textbook for the 11th grade of an 11-year secondary school, for basic and advanced levels. N.D. Lisov, L.V. Kamlyuk, N.A. Lemeza et al. Ed. N.D. Lisova.- Mn.: Belarus, 2002.- 279 p.
Contents of the textbook General Biology: Textbook for 11th grade:
- § 2. Population is a structural unit of a species. Population characteristics
- § 6. Ecosystem. Connections of organisms in an ecosystem. Biogeocenosis, structure of biogeocenosis
- § 7. Movement of matter and energy in an ecosystem. Power circuits and networks
- § 9. The circulation of substances and the flow of energy in ecosystems. Productivity of biocenoses
- § 13. Prerequisites for the emergence of the evolutionary theory of Charles Darwin
- § 14. General characteristics of the evolutionary theory of Charles Darwin
- § 18. Development of evolutionary theory in the post-Darwinian period. Synthetic theory of evolution
- § 19. Population is an elementary unit of evolution. Prerequisites for evolution
- § 27. Development of ideas about the origin of life. Hypotheses about the origin of life on Earth
- § 32. The main stages of the evolution of flora and fauna
- § 33. The diversity of the modern organic world. Principles of taxonomy
Chapter 1. Species - a unit of existence of living organisms
Chapter 2. Relationships of species, populations with the environment. Ecosystems
Chapter 3. Formation of evolutionary views
Chapter 4. Modern ideas about evolution
Chapter 5. Origin and development of life on Earth
Chapter 6. Origin and evolution of man
