GENERAL BIOLOGY
EVOLUTION. EVOLUTIONARY TEACHING
EVIDENCE OF EVOLUTION
Biological evolution is the historical process of development of the organic world, which is accompanied by changes in organisms, the extinction of some and the appearance of others. Modern science operates with many facts that indicate evolutionary processes.
Embryological evidence of evolution.
In the first half of the 19th century. The theory of “germinal similarity” begins to develop. The Russian scientist Karl Baer (1792-1876) found that in the early stages of embryo development there is a great similarity between embryos of different species within the type.
The works of F. Müller and E. Haeckel gave them the opportunity to formulate the biogenetic law: “ontogenesis is a short and rapid repetition of phylogeny.” Later, the interpretation of the biogenetic law was developed and clarified by V.M. Severtsovim: “in ontogenesis, the embryonic stages of the ancestors are repeated.” The embryos at the early stages of development have the greatest similarity. General characteristics of a type are formed in the process of embryogenesis earlier than special ones. Thus, all vertebrate embryos at stage I have gill slits and a two-chambered heart. At the middle stages, characteristics characteristic of each class appear, and only at later stages the characteristics of the species are formed.
Comparative anatomical and morphological evidence of evolution.
Proof of the unity of origin of all living things is the cellular structure of organisms, a single structure plan of organs and their evolutionary changes.
Homologous organs have a similar structure, a common origin, and perform both the same and different functions. The presence of homologous organs makes it possible to prove the historical relationship of different species. Primary morphological similarity is replaced to varying degrees by differences acquired during the process of divergence. A typical example of homologous organs are the limbs of vertebrates, which have the same structural plan regardless of the functions they perform.
Some plant organs develop morphologically from germ layers and are modified leaves (antennae, spines, stamens).
Analogous organs are secondary, morphological similarities not inherited from common ancestors of organisms of different systematic groups. Similar organs are similar in their functions and develop through the process of convergence. They indicate the uniformity of adaptations that arise in the process of evolution under the same environmental conditions as a result of natural selection. For example, similar animal organs -butterfly and bird wings. This adaptation to flight in butterflies developed from the chitinous cover, and in birds - from the internal skeleton of the forelimbs and feather cover. Phylogenetically, these organs were formed differently, but perform the same function - animals are used for flight. Sometimes similar organs acquire exceptional similarities, such as the eyes of cephalopods and terrestrial vertebrates. They have the same general plan of structure, similar structural elements, although they develop from different embryonic leaves in ontogenesis and are completely unrelated to each other. The similarity is explained only by the physical nature of light.
An example of similar organs is the spines of plants, which protect them from being eaten by animals. Spines can develop from leaves (barberry), stipules (white acacia), shoots (hawthorn), bark (blackberry). They are similar only in appearance and in the functions they perform.
Vestigial organs, relatively simplified or underdeveloped structures that have lost their original purpose. They are laid during embryonic development, but do not fully develop. Sometimes rudiments perform different functions compared to homologous organs of other organisms. Thus, the rudimentary human appendix performs the function of lymph formation, in contrast to the homologous organ - the cecum in herbivores. Rudiments of the pelvic girdle of a whale and the limbs of a python confirm the fact that whales originated from terrestrial quadrupeds, and pythons - from ancestors with developed limbs.
Atavism is the phenomenon of a return to ancestral forms that is observed in individual individuals. For example, zebra-like coloring in foals, rich nipples in humans.
Biogeographic evidence for evolution.
The study of the flora and fauna of different continents makes it possible to reconstruct the general course of the evolutionary process and identify several zoogeographic zones with similar terrestrial animals.
1. The Holarctic region unites the Palearctic (Eurasia) and Neoarctic (North America) regions.
2. Neotropical region (South America).
3. Ethiopian region (Africa).
4. Indo-Malayan region (Indochina, Malaysia, Philippines).
5. Australian region.
In each of these areas there is a great similarity between the animal and plant worlds. The regions differ from each other by certain endemic groups.
Endemics are species, genera, families of plants or animals, the distribution of which is limited to a small geographical area, that is, flora or fauna specific to a given area. The development of endemicity is most often associated with geographic isolation. For example, the earliest separation of Australia from the southern continent of Gondwana (more than 120 million years) led to the independent development of a number of animals. Without feeling pressure from predators, which are absent in Australia, monotreme mammals - primal beasts - have been preserved here: the platypus and the echidna; marsupials: kangaroo, koala.
The flora and fauna of the Palearctic and Neoarctic regions, on the contrary, are similar to each other. For example, closely related trees include American and European maples, ash trees, pine trees, and spruce trees. Mammals such as moose, martens, minks, and polar bears live in North America and Eurasia. The American bison is represented by a family species - the European bison. Such similarities indicate the long-term unity of the two continents.
Paleontological evidence of evolution.
Paleontology studies fossil organisms and allows us to establish the historical process and causes of change in the organic world. Based on paleontological finds, a history of the development of the organic world has been compiled.
Fossil transitional forms are forms of organisms that combine ancient and modern groups. They help restore the phylogeny of individual groups. Representatives: Archeopteryx - a transitional form between reptiles and birds; Inostrantseviya is a transitional form between reptiles and mammals; psilophytes are a transitional form between algae and terrestrial plants.
Paleontological series are composed of fossil forms and reflect the course of phylogenesis (historical development) of the species. Such rows exist for horses, elephants, and rhinoceroses. The first paleontological series of horses was compiled by V. A. Kovalevsky (1842-1883).
Relics are rare species of plants or animals that have remained to exist in a given territory and have been preserved from past geological times. They are characterized by signs of extinct groups of past eras. The study of relict forms allows us to restore the appearance of missing organisms, recreate their living conditions and way of life. Hatteria is a representative of ancient primitive reptiles. Such reptiles lived in the Jurassic and Cretaceous periods. The cross-finned fish coelacanth has been known since the Early Devonian. These animals gave rise to land vertebrates. Ginkgo is the most primitive form of gymnosperm. The leaves are large, fan-shaped, November plants. On the territory of Ukraine, among the relict plants, yellow azalea, chalk pine, and thousand berry have been preserved. Among the relict animals there are the common muskrat, the bandage and other animals.
Comparison of modern primitive and progressive forms of organisms makes it possible to restore some of the characteristics of the supposed ancestors of the progressive form and to analyze the course of the evolutionary process.
II. Embryological evidence (embryology studies the embryonic development of an organism).
1. Similarity of embryos.
a) The structure of the chordate embryo consistently resembles the body of other types of animals:
oocyte - protozoa;
· gastrula – coelenterates;
· roundworms;
· representatives of the Skullless subtype.
b) This indicates the common origin of all chordates.
2. Divergence of embryonic characteristics (embryonic divergence).
a) As development progresses, the similarities between embryos of different species weaken.
b) Characteristics of the genus appear first, and then the species.
· The initial similarity in the structure of the head between a child and a baby monkey gradually disappears.
3. Haeckel-Müller biogenetic law: each individual in individual development (ontogenesis) briefly and concisely repeats the history of the development of its species (phylogeny).
a) Examples in animals:
· The vessels of the embryos of land vertebrates are similar to the vessels of fish;
· The human embryo has gill slits.
· Butterfly caterpillars and beetle larvae are similar in structure to annelids.
· Amphibian tadpoles are similar to fish.
b) Examples in plants:
· Bud scales in plant buds develop like leaves.
· The petals of the buds are green at first, and then acquire their characteristic color.
· From a moss spore, a green thread first appears, similar to a filamentous algae (pregrown).
c) Amendments to the biogenetic law.
· In embryos, the repetition of phylogeny may be disrupted due to adaptations to living conditions during ontogenesis. Appear: embryonic membranes, a yolk sac in fish eggs, external gills in a tadpole, a cocoon in a silkworm.
· Ontogenesis does not fully reflect phylogeny due to the appearance of mutations that change the course of development of the embryo (in the snake embryo, all vertebrae are formed at once, i.e., their number does not increase gradually; in birds, the five-fingered stage of limb development has fallen; the embryo develops 4 fingers, not 5, only 3 fingers grow in the wing).
· In ontogenesis, there is a repetition of the embryonic stages of development, and not of the adult forms (Lancelet repeats in ontogenesis the general stages with the free-swimming larva of the ascidian, and not with its adult, fixed form).
d) Modern ideas about the biogenetic law.
· Severtsov showed that due to changes in development, some stages of embryo development can be lost; changes in the organs of the embryo occur that were not present in the ancestors; new species arise; new characteristics are revealed (for example, tailed (newts) and tailless (frogs) amphibians descended from the same ancestor: the newt larva is long, because it has many vertebrae, in the frog larva the number of vertebrae has decreased due to mutation; the lizard embryo has fewer vertebrae, than in the snake embryo, due to developmental mutations).
III. Biogeographical evidence (Biogeography studies the distribution of animals and plants on Earth).
1. There are 5 zoogeographic zones that do not differ in classes and types of animals:
a) Holarctic;
b) Indo-Malaysian;
c) Ethiopian;
d) Australian;
e) Neotropical zone.
2. Zones differ by families, orders and genera.
a) In Australia, all mammals are marsupials.
b) New Zealand is home to the only representative of the order of beak-headed lizards - the hatteria.
c) There are American and European species of maple, ash, and pine.
3. Reasons for the similarities and differences between fauna and flora.
a) Isolation of habitats.
· If the isolation occurred recently, then there are more similarities than differences: the Bering Strait was formed recently, so the fauna of Asia differs little from the fauna of America; North and South America recently united, so their faunas are different; Australia separated from the rest of the continents a long time ago, therefore it has a unique flora and fauna; evolution was slow, since Australia is relatively small; The fauna and flora of islands and closed reservoirs are unique.
4. The modern geographical distribution of animals and plants can only be explained from an evolutionary point of view.
IV. Paleontological (Palaeontology studies fossil organisms, their living conditions and burials).
1. Change of fauna and flora on Earth.
a) In the most ancient layers, only invertebrates were found.
b) The younger the layer, the closer the remains are to modern species.
c) With the help of paleontological finds, it was possible to establish phylogenetic series and transitional forms.
2. Fossil transitional forms– forms of organisms that combine the characteristics of older and younger forms.
a) Animal-toothed reptiles were discovered on the Northern Dvina (genus Inostrantseviya). They were similar to mammals in the structure of the following organs: skull; spine; limbs located not on the sides of the body, as in reptiles, but under the body, as in mammals; teeth differentiated into canines, incisors and molars.
b) Archeopteryx- a transitional form between birds and reptiles, discovered in the layers of the Jurassic period (150 million years ago).
· Signs of birds: hind limbs with tarsus, wings and feathers, external resemblance.
· Signs of reptiles: long tail consisting of vertebrae; abdominal ribs; presence of teeth; claws on the forelimb.
· It flew poorly for the following reasons: the sternum was without a keel, i.e. pectoral muscles were weak; the spine and ribs were not rigidly supported, as in birds.
V) Psilophytes– a transitional form between algae and land plants.
· Derived from green algae.
· Higher spore-bearing vascular plants - mosses, horsetails, and ferns - originated from psilophytes.
· Appeared in the Silurian and spread in the Devonian.
· Differences from algae and higher spores: psilophytes – herbaceous and woody plants growing along the shores of the seas; had a branched stem with scales; the skin had stomata; the underground stem resembled rhizomes with rhizoids; the stem was differentiated into conductive, integumentary and mechanical tissues.
3. Phylogenetic series– series of certain forms that successively replaced each other during evolution (phylogeny).
a) V.O. Kovalevsky restored the evolution of the horse, constructing its phylogenetic series.
· Eohippus, who lived in the Paleogene, was the size of a fox, had a four-toed forelimb and a three-toed hind limb. The teeth were tuberculate (a sign of omnivory).
· In the Neogene, the climate became more arid, the vegetation changed, Eohippus evolved through a number of forms: Eohippus, Merigippus, Hipparion, modern horse.
· The signs of eohippus have changed: the legs have lengthened; the claw turned into a hoof; the support surface was reduced, so the number of fingers was reduced to one; fast running led to strengthening of the spine; the transition to roughage led to the formation of folded teeth.
The evidence for the animal origin of man is based on evidence for the evolution of the organic world.
I. Paleontological evidence
1. Fossil forms.
2. Transitional forms.
3. Phylogenetic series.
Paleontological finds make it possible to restore the appearance of extinct animals, their structure, similarities and differences with modern species. This makes it possible to trace the development of the organic world over time. For example, in ancient geological strata the remains of only representatives of invertebrates were found, in later ones - chordates, and in young sediments - animals similar to modern ones.
Paleontological finds confirm the existence of continuity between various systematic groups. In some cases, it was possible to find fossil forms (for example, Sinanthropus), in others, transitional forms, combining the characteristics of ancient and historically younger representatives.
In anthropology, such forms are: dryopithecines, australopithecines, etc.
In the animal world, such forms are: Archeopteryx - a transitional form between reptiles and birds; inostracevia - a transitional form between reptiles and mammals; psilophytes - between algae and land plants.
Based on such finds, it is possible to establish phylogenetic (paleontological) series - forms that successively replace each other in the process of evolution.
Thus, paleontological finds clearly indicate that as we move from more ancient earth layers to modern ones, there is a gradual increase in the level of organization of animals and plants, bringing them closer to modern ones.
II. Biogeographical evidence
1. Comparison of species composition with the history of territories.
2. Island forms.
3. Relics.
Biogeography studies the patterns of distribution of plant (flora) and animal (fauna) worlds on Earth.
It has been established: the earlier the isolation of individual parts of the planet occurred, the greater the differences between the organisms inhabiting these territories - island forms.
Thus, the fauna of Australia is very peculiar: many Eurasid animal groups are absent here, but those that are not found in other regions of the Earth have been preserved, for example, oviparous marsupial mammals (platypus, kangaroo, etc.). At the same time, the fauna of some islands is similar to the mainland (for example, the British Isles, Sakhalin), which indicates their recent isolation from the continent. Consequently, the distribution of animal and plant species on the surface of the planet reflects the process of the historical development of the Earth and the evolution of living things.
Relics are living species with a complex of characteristics characteristic of long-extinct groups of past eras. Relict forms indicate the flora and fauna of the Earth's distant past.
Examples of relict forms are:
1. Hatteria is a reptile native to New Zealand. This species is the only living representative of the Proto-Lizard subclass in the Reptile class.
2. Coelacanth (coelocanthus) is a lobe-finned fish that lives in deep-sea areas off the coast of East Africa. The only representative of the lobe-finned fish order, closest to terrestrial vertebrates.
3. Ginkgo biloba is a relict plant. Currently common in China and Japan only as an ornamental plant. The appearance of ginkgo allows us to imagine tree forms that became extinct in the Jurassic period.
In anthropology, a relict hominid means the mythological “Bigfoot”.
III. Comparative embryological
1. K. Baer’s law of germinal similarity.
2. Haeckel-Müller biogenetic law.
3. The principle of recapitulation.
Embryology is a science that studies the embryonic development of organisms. Data from comparative embryology indicate similarities in the embryonic development of all vertebrates.
Karl Baer's law of germline similarity(1828) (Darwin gave this name to the law), indicates a common origin: embryos of different systematic groups are much more similar to each other than adult forms of the same species.
In the process of ontogenesis, the characteristics of the type appear first, then the class, the order, and the last to appear are the characteristics of the species.
Main provisions of the law:
1) In embryonic development, embryos of animals of the same type successively go through stages - zygote, blastula, hastrula, histogenesis, organogenesis;
2) embryos in their development move from
more general characteristics to more specific ones;
3) embryos of different species gradually separate from each other, acquiring individual characteristics.
German scientists F. Müller (1864) and E. Haeckel (1866) independently formulated a biogenetic law, which was called the Haeckel-Müller Law: the embryo in the process of individual development (ontogenesis) briefly repeats the history of the development of the species (phylogeny).
The repetition of structures characteristic of ancestors in the embryogenesis of descendants was called - recapitulations.
Examples of recapitulation are: notochord, five pairs of nipples, a large number of hair buds, cartilaginous spine, gill arches, 6-7 finger buds, general stages of intestinal development, the presence of a cloaca, the unity of the digestive and respiratory systems, phylogenetic development of the heart and main vessels, gill slits , all stages of development of the intestinal tube, recapitulation in the development of the kidney (prerenal, primary, secondary), undifferentiated gonads, gonads in the abdominal cavity, paired Müllerian canal from which the oviduct, uterus, vagina is formed; main stages of phylogenesis of the nervous system (three brain vesicles).
Not only morphological characteristics recapitulate, but also biochemical and physiological ones - the release of ammonia by the embryo, and in the later stages of development - uric acid.
According to comparative embryological data, in the early stages of embryonic development, the human embryo develops signs characteristic of the Chordata type, later the characters of the Vertebrates subtype are formed, then the Mammals class, the Placental subclass, and the Primates order.
IV. Comparative anatomical
1. General plan of the body structure.
2. Homologous organs.
3. Rudiments and atavisms.
Comparative anatomy studies the similarities and differences in the structure of organisms. The first convincing proof of the unity of the organic world was the creation of the cell theory.
Unified building plan: all chordates are characterized by the presence of an axial skeleton - the notochord; above the notochord there is a neural tube, under the notochord there is a digestive tube, and on the ventral side there is a central blood vessel.
Availability homologous organs - organs that have a common origin and a similar structure, but perform different functions.
Homologous are the forelimbs of a mole and a frog, the wings of birds, the flippers of seals, the forelegs of a horse and human hands.
In humans, like in all chordates, organs and organ systems have a similar structure and perform similar functions. Like all mammals, humans have a left aortic arch, a constant body temperature, a diaphragm, etc.
Organs that have different structures and origins, but perform the same functions are called similar(eg butterfly and bird wings). To establish the relationship between organisms and prove evolution, similar organs are not important.
Rudiments- undeveloped organs that, during the process of evolution, lost their significance, but were present in our ancestors. The presence of rudiments can only be explained
the fact that in our ancestors these organs functioned and were well developed, but during the process of evolution they lost their importance.
In humans, there are about 100 of them: wisdom teeth, poorly developed hair, muscles that move the auricle, tailbone, auricles, appendix, male uterus, muscles that raise the hair; rudiments of vocal sacs in the larynx; brow ridges; 12-pair of ribs; wisdom teeth, epicanthus, variable number of coccygeal vertebrae, brachiocephalic trunk.
Many rudiments exist only in the embryonic period and then disappear.
The rudiments are characterized by variability: from complete absence to significant development, which is of practical importance for the doctor, especially the surgeon.
Atavisms- manifestation in descendants of characteristics characteristic of distant ancestors. Unlike rudiments, they are deviations from the norm.
Possible reasons for the formation of atavisms: mutations of regulatory genes of morphogenesis.
There are three types of atavisms:
1) underdevelopment of organs when they were at the stage of recapitulation - three-chamber heart, “cleft palate”;
2) preservation and further development of recapitulation characteristic of ancestors - preservation of the right aortic arch;
3) violation of the movement of organs in ontogenesis - the heart in the cervical region, undescended testicles.
Atavisms can be neutral: strong protrusion of the fangs, strong development of the muscles that move the auricle; and can manifest themselves in the form of developmental anomalies or deformities: hypertrichosis (increased hairiness), cervical fistula, diaphragmatic hernia, patent ductus botallus, hole in the interventricular septum. Polynipple, polymastia - an increase in the number of mammary glands, non-fusion of the spinous processes of the vertebrae (spina bifida), caudal spine, polydactyly, flat feet, narrow chest, clubfoot, high scapula, non-fusion of the hard palate - “cleft palate”, atavisms of the dental system, bifurcated tongue, neck fistulas, shortening of the intestine, preservation of the cloaca (common opening for the rectum and genitourinary opening), fistulas between the esophagus and trachea, underdevelopment and even aplasia of the diaphragm, two-chambered heart, heart septal defects, preservation of both arches, preservation of the ductus bollus, transposition vessels (the left arch departs from the right ventricle, and the right aortic arch departs from the left ventricle), pelvic location of the kidney, hermaphroditism, cryptorchidism, bicornuate uterus, uterine duplication, undeveloped cerebral cortex (proencephaly), agyria (absence of brain convolutions).
Comparative anatomical study of organisms made it possible to identify modern transitional forms. For example, the first animals (echidna, platypus) have a cloaca, lay eggs like reptiles, but feed their young with milk like mammals. The study of transitional forms makes it possible to establish kinship between representatives of different systematic groups.
V. Molecular genetic evidence
1. The universality of the genetic code.
2. Similarity to proteins and nucleotide sequences.
Similarities between humans and apes (similarities between pongids and hominids) There is much evidence of the relationship between humans and modern apes. Humans are closest to gorilla and chimpanzee
I. General anatomical features
Humans and gorilla have 385 common anatomical features, humans and chimpanzees have 369, humans and orangutans have 359: - binocular vision, progressive development of vision and touch with weakening of the sense of smell, development of facial muscles, grasping type limbs, opposition of the thumb to the rest, reduction caudal spine, the presence of an appendix, a large number of convolutions in the cerebral hemispheres, the presence of papillary patterns on the fingers, palms and soles, fingernails, developed collarbones, a wide flat chest, nails instead of claws, a shoulder joint that allows movement with a range of up to 180° .
II Similarity of karyotypes
■ All great apes have a diploid chromosome number of 2/n = 48. In humans, 2n = 46.
It has now been established that the 2nd pair of human chromosomes is a product of the fusion of two monkey chromosomes (interchromosomal aberration - translocation).
■ Homology of 13 pairs of chromosomes between pongidae and humans has been revealed, which is manifested in the same pattern of chromosome striations (the same arrangement of genes).
■ The cross-striation of all chromosomes is very similar. The percentage of gene similarity in humans and chimpanzees reaches 91, and in humans and apes it reaches 66.
■ Analysis of the amino acid sequences in human and chimpanzee proteins shows that they are 99% identical.
III. Morphological similarities
The structure of proteins is similar: for example, hemoglobin. The blood groups of gorillas and chimpanzees are very close to the ABO system group of apes and humans, the blood of the pygmy chimpanzee Bonobos corresponding to humans.
The Rh factor antigen has been found in both humans and the lower ape, the rhesus macaque.
Similarities are observed in the course of various diseases, which is especially valuable in biological and medical research.
The similarity is based on Vavilov’s law of homologous series. In experiments, diseases such as syphilis, typhoid fever, cholera, tuberculosis, etc. were obtained in apes.
Apes are close to humans in terms of the duration of pregnancy, limited fertility, and timing of puberty.
Differences between humans and apes
1. The most characteristic feature that distinguishes humans from apes is the progressive development of the brain. In addition to its greater mass, the human brain has other important features:
The frontal and parietal lobes are more developed, where the most important centers of mental activity and speech are concentrated (the second signaling system);
The number of small furrows has significantly increased;
A significant part of the human cerebral cortex is associated with speech. New properties have emerged - sound and written language, abstract thinking.
2. Upright walking (bipedia) with a heel-to-toe position and work activity required the restructuring of many organs.
Humans are the only modern mammals that walk on two limbs. Some monkeys are also capable of walking upright, but only for a short time.
Adaptations to bipedal locomotion.
The more or less straightened position of the body and the transfer of the center also mainly to the hind limbs dramatically changed the relationship between all of us in the animal:
The chest became wider and shorter,
The spinal column gradually lost its arch shape, characteristic of all animals that move on four legs, and acquired a 3-shaped shape, which gave it flexibility (two lordosis and two kyphosis),
Displacement of the foramen magnum,
The pelvis is expanded, as it takes on the pressure of the internal organs, the chest is flattened, at more powerful lower limbs (bones and muscles of the lower limb (the femur can withstand a load of up to 1650 kg), arched foot (unlike the flat foot of monkeys),
Inactive first toe
The upper limbs, which ceased to function as supports when moving, became shorter and less massive. They began to make various movements. This turned out to be very useful, as it made it easier to get food.
3. Complex of the “labor hand” -
The muscles of the thumb are better developed,
Increased mobility and strength of the hand,
High degree of opposition of the thumb on the hand,
The parts of the brain that provide fine movements of the hand are well developed.
4. Changes in the structure of the skull are associated with the formation of consciousness and the development of the second signaling system.
In the skull, the brain section predominates over the facial section,
The brow ridges are less developed,
Reduced mass of the lower jaw,
The profile of the face is straightened,
Small size of teeth (especially canines compared to animals),
It is typical for humans to have a chin protuberance on the lower jaw.
5. Speech function
Development of cartilage and ligaments of the larynx,
The chin protrusion is pronounced. The formation of the chin is associated with the emergence of speech and concomitant changes in the bones of the facial skull.
The development of speech became possible thanks to the development of two parts of the nervous system: Broca's area, which made it possible to quickly and relatively accurately describe accumulated experience with ordered sets of words, and Wernicke's area, which allows us to just as quickly understand and adopt this experience conveyed by speech - the result of which was the acceleration of verbal exchange of information and simplifying the acquisition of new concepts.
6. A person has experienced hair loss.
7. The fundamental difference between Homo sapiens and all animals is the ability to purposefully manufacture tools of labor (purposeful labor activity), which allows modern man to move from subjugating nature to intelligently managing it.
Signs such as:
1- upright posture (bipedia),
2- hand adapted to work and
3- highly developed brain - called the hominid triad. It was in the direction of its formation that the evolution of the human hominid line went.
All of the above examples indicate that, despite the presence of a number of similar characteristics, a person is significantly different from co temporary monkeys.
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.
Similarity of embryos. Biogenetic law
The study of embryonic and postembryonic development of animals made it possible to find common features in these processes and formulate the law of embryonic similarity (K. Baer) and the biogenetic law (F. Müller and E. Haeckel), which are of great importance for understanding evolution.
All multicellular organisms develop from a fertilized egg. The processes of embryo development in animals belonging to the same type are largely similar. In all chordates, in the embryonic period, an axial skeleton is formed - the notochord, and a neural tube appears. The structural plan of chordates is also the same. In the early stages of development, vertebrate embryos are extremely similar (Fig. 24).
These facts confirm the validity of the law of embryonic similarity formulated by K. Baer: “Embryos exhibit, already from the earliest stages, a certain general similarity within the type.” The similarity of the embryos serves as evidence of their common origin. Subsequently, the structure of the embryos reveals characteristics of class, genus, species, and, finally, characteristics characteristic of a given individual. The divergence of characteristics of embryos during development is called embryonic divergence and reflects the evolution of a particular systematic group of animals.
The great similarity of embryos in the early stages of development and the appearance of differences in later stages has its own explanation. The study of embryonic variability shows that all stages of development are variable. The mutation process also affects genes that determine the structural and metabolic features of the youngest embryos. But the structures that arise in early embryos (ancient characteristics characteristic of distant ancestors) play a very important role in the processes of further development. Changes in the early stages usually lead to underdevelopment and death. On the contrary, changes in later stages may be beneficial for the organism and are therefore picked up by natural selection.
The appearance in the embryonic period of development of modern animal characters characteristic of distant ancestors reflects evolutionary transformations in the structure of organs.
In its development, the organism passes through a single-celled stage (zygote stage), which can be considered as a repetition of the phylogenetic stage of the primitive amoeba. In all vertebrates, including their highest representatives, a notochord is formed, which is then replaced by a spine, and in their ancestors, judging by the lancelet, the notochord remained throughout their lives.
During the embryonic development of birds and mammals, including humans, gill slits and corresponding septa appear in the pharynx. The fact of the formation of parts of the gill apparatus in the embryos of terrestrial vertebrates is explained by their origin from fish-like ancestors that breathed with gills. The structure of the heart of the human embryo during this period resembles the structure of this organ in fish.
Such examples indicate a deep connection between the individual development of organisms and their historical development. This connection is expressed in the biogenetic law formulated by F. Müller and E. Haeckel in the 19th century: ontogenesis (individual development) of each individual is a short and rapid repetition of phylogeny (historical development) of the species to which this individual belongs.
The biogenetic law played a prominent role in the development of evolutionary ideas. A major contribution to deepening the understanding of the evolutionary role of embryonic transformations belongs to A. N. Severtsov. He established that in individual development the characteristics are repeated not of adult ancestors, but of their embryos.
Phylogenesis is now considered not as a change in the sequences of a number of adult forms, but as a historical series of ontogenies selected by natural selection. Entire ontogenies are always subject to selection, and only those that, despite the influence of unfavorable environmental factors, survive at all stages of development, leaving viable offspring. Thus, the basis of phylogeny is the changes occurring in the ontogeny of individual individuals.
Paleontological evidence. A comparison of fossil remains from earth layers of different geological eras convincingly indicates changes in the organic world over time. Paleontological data provide a wealth of material about the successive connections between various systematic groups. In some cases, it was possible to establish transitional forms, in others - phylogenetic series, that is, series of species successively replacing one another.
Fossil transitional forms:
A) Archeopteryx- a transitional form between birds and reptiles, discovered in the layers of the Jurassic period (150 million years ago). Signs of birds: hind limbs with a tarsus, the presence of feathers, external resemblance, wings. Signs of reptiles: a long tail consisting of vertebrae, abdominal ribs, the presence of teeth, bones on the forelimb;
B) psilophytes- a transitional form between algae and terrestrial plants.
Phylogenetic series. V. O. Kovalsky restored the evolution of the horse, constructing its phylogenetic series (Fig. 25).
The evolution of the horse covers a fairly large period of time. The oldest ancestor of the horse dates back to the beginning of the Tertiary period, while the modern horse dates back to the Quaternary period. Species of the genus Eucus were small forest animals 30 cm high. They had four toes on their feet, which made it easier to walk and run on the marshy soil of forest swamps. Judging by the teeth, these animals ate soft plant foods. They belong to the lower Eocene of North America. This form is followed by the Middle Eocene Orohippus, in which four toes were still developed on the front legs. In the Middle Eocene, epihippus appears, in which the fourth digit is reduced. In the Oligocene, a descendant of previous forms lived - Mesohippus. He has only three toes on his feet, with the middle finger being noticeably more developed than the others. The height of the animals reaches 45 cm.
Changes in the dental system begin to appear. The tuberculated front teeth of Eohippus, adapted to soft plant foods, turn into teeth with grooves. Evolution also affects molars; they become more adapted to coarse steppe plant food. In the Upper Oligocene, mesohippus gives way to a number of forms: myochypus, and in the lower Miocene - para-hippus. Parahippus is the ancestor of the next stage of the horse series - merichippus. Meryhippus were undoubtedly inhabitants of open spaces, and in different species of this genus there was a process of shortening of the lateral fingers: in some species the fingers were longer, in others shorter, in the latter case approaching the fleet-footed one-toed horses.
Finally, in Pliohyppus, who lived in the Pliocene, this process ends with the formation of a new form, the ancient one-toed horse - Plesippus. In shape and size, the latter is close to the modern horse, known since the Pleistocene.
Originating in America, the modern form of the horse then spreads to Eurasia among several species. Ultimately, all American horses died out, but the European ones survived and then came to America a second time. This time they were brought here by Europeans at the beginning of the 16th century. Thus, the evolution of horses convincingly shows the process of evolution leading to the emergence of new species by transforming their ancestors.