Evolution theory science explanation for origin of life and species
The term evolution refers to many concepts, will be taken here in the sense of biological evolution, precisely defined later. In this sense, it is a relatively recent employment. Neither Lamarck nor Darwin used it. In the eighteenth century, was called the first development phases through which the living pass before reaching his perfect form, it was somehow synonymous with development, it covers embryogenesis and postembryonic growth
(with or without transformation) to the adult form suitable for reproduction. Then, under the influence of preformists (Haller, Bonnet, Meckel, Reaumur ...), the term applied to the evolution theory that the entire organization to be present in the seed: "The germ preexists fertilization. All essential parts have coexisted at the same time. Development seems to precede each other. Their consistency, their relative proportions, their shape, their situation gradually undergo very large changes "(C. Bonnet, Considerations organized bodies, t. Complete Works III, Neuchâtel, 1779, p. 111 and 112). The preformists were then qualified evolutionists, they are opposed to épigénistes to which the embryo is formed gradually from an amorphous plasma, causing a change in another.
Therefore, the reasons are obvious why the term evolution could come from the pen of Lamarck, convinced épigéniste to designate its doctrine of parentage species. For unclear reasons, Darwin left, too, his doctrine unnamed.
If this is Herbert Spencer who first used the term evolution in its present sense, it is responsible for having known for his books which was broadcast worldwide. Thomas Huxley, the most ardent propagandists of Darwinism, widely used the term evolution, now universally used.
We define biological evolution as the process by which, over the ages, succeed and create, while varying the plant and animal species.
Evolution is the continuity of living beings in a dissimilarity oriented. Heredity, subject of genetics studies the succession of living beings in the likeness. One is the change, the other stability.
1. History of evolutionism:
Many naturalists and philosophers who were seen precursors of evolutionism. In antiquity, the names of Democritus (460-370 BC.), Epicurus (341-270 BC.), Lucretius (98-55 BC. J.-C .) are spoken, for modern times, it is called Maillet (1656-1738), Buffon (1707-1788), Maupertuis (1698-1759), Diderot (1713-1784), especially his posthumous works, Cabanis (1757-1808). But, in fact, none had a clear view of evolution; their writings contain some thoughts that evoke transformists principles; it emerges no general conception of the genesis and history of living beings. Moreover, in the absence of positive data, no theory of evolution is admissible.
The concept of biological evolution has taken shape with the writings of Jean-Baptiste de Monet, Chevalier de Lamarck (Opening of the course, 27 Floreal X; Zoological Philosophy, 1809). The thought of his alleged predecessors seems to have influenced anything.
In 1858, two English naturalist, Charles R. Darwin, forty-nine years, and Alfred R. Wallace, thirty-five years after completing long journeys in the tropics offer independently of the other a theory explaining the genesis of new species, both animal and vegetable, descent direct and continuous. Individuals vary them persist only fit, fortuitously, the circumstances natural selection is the agent trainer of new species. C. Lyell and J. Hooker presented the same day, at the Linnean Society of London, a text, written jointly by Darwin and Wallace, entitled On the Tendency of Species to Form Varieties, and the Perpetuation of Varieties and Species by Natural Selection. Subsequently, Wallace, while successfully pursuing his scientific career but showing exemplary modesty, faded before Darwin, and, had the good fortune to be the main champion of evolution.
In the early twentieth century, Darwinism was supported by the "mutationism" theory devised by the botanist Hugo de Vries (1848-1935), Darwinism has adopted the postulate that the mutations (spikes hereditary, any ) are materials in which the development is carried out by natural selection. The study of natural selection from theoretical models tried several mathematicians: Volterra (1860-1940), Fisher (1930), Sewall Wright (1969), among others. By way of deduction, applying the laws of heredity, they fired rules expressed in mathematical formulas. Contemporary authors, while remaining strictly faithful to the principles laid down by Darwin, and claim to speak for the new neo-Darwinism. Julian Huxley presented their arguments in detail and talent, in his book Evolution, the Modern Synthesis (1942).
Over the last twenty years, a new way of thinking, unorthodox, was born, he admits neither universal nor omnipotence of natural selection and random places a very large part in the conservation of new structures (Kimura and Ohta, 1971).
2. Evidences for evolution:
The evolution has been written, is not a hypothesis but a fact. As evidence has been produced in its favor that this statement is required. It is no longer a biologist for doubt. Only religious sects do not accept.
* paleontological evidences:
These are the strongest because they give the image of what was the actual evolution over time. Chemists and physicists have delivered to paleontologist techniques that allow him to date fossils. We note that, in general, both animal and vegetable kingdoms went simple shapes to form more complex.
- flora:
The achievement of multicellular algae became slowly forms that we discover in the Silurian deposits were already well advanced and were preceded, in all likelihood, by simpler types.
The Nematophycus, which were thallus up to one meter in diameter, floated giant kelp in the Silurian seas. The first terrestrial plants, the Psilophytales are found in sediments of Middle and Upper Devonian. The Rhynia, which are among the best known, consisted of a rhizome root hairs, which are erected on slender stems ending in sporangia. The Psilophytales, who owned vessels were no longer mere Thallophytes, but vascular Cryptogams. We know what kind of development they took from the Upper Devonian to Carboniferous reach their peak.
The Middle Carboniferous, the phanerogams are emerging with Cordaites. Subsequently there add some Cycads and Conifers with the kind Walchia. The ancestor of Ginkgo is known Permian (Ginkgophyllum).
The plant kingdom, over time, is progressively complicated simple shapes appeared the first, complex shapes, the latest.
- Wildlife:
The Precambrian era that spans nearly 800 million years has been fruitful in producing new products. She was born protozoa which are likely a heterogeneous group, whose components are derived from distinct ancestral strains.
The animal crossed a huge step when, unicellular, he became multicellular and ordered its cells in a closed bag defining a space, a draft internal environment. At the same time, he formed specialized cells in reproduction and holding power of all the characters to be clean; these cells or gametes ensure the survival of the species: they are potentially immortal. Such a simple still exists in salt water: the Trichoplax. Probably time he antécambrienne a time.
Cambrian, we know sponges, cnidarians, annelids, molluscs, Onychophora, Crustaceans, Mérostomes, trilobites and brachiopods. However, no fossil attributable with certainty to a vertebrate belongs to this period.
Silurian groups that existed in the Cambrian, change in perfecting: Crinoids are complicated; Trilobites show forms more varied, the Nautilidés among cephalopods, diversify. Late Silurian, the Scorpions are the first to go on Arthropods mud or on land. At the same time, the vertebrates are emerging with Ostracodermi, which belong to the class of Agnathes, that is to say, lampreys, and archaic characters together (no lower jaw and vertebrae individualized presence of two semicircular canals, one nostril median, etc..) to highly evolved characters (pineal eye, electrical components, etc.)..
Devonian, the Mérostomes reach their peak, while emerging new types of Ammonites and placoderms, cartilaginous fish and dermal skeletal plates, provided with a lower mandible. Upper Devonian, we discover the Elasmobranchii.
Carboniferous and Permian, Myriapoda, Insects, Arachnids fossilize in continental deposits and coastlines. The bony fishes are already recognizable, but still retain archaic structures. The first tetrapod vertebrates, the Stegocephalia, appeared in the Devonian aspects of Pisces close crossopterygians evolve in multiple directions. The Permian Reptiles: Prosauriens and theromorphs, begin with forms of minimal size and terrestrial habits, while Stegocephalia disappear. Very early on, theromorphs moving towards mammalian organization.
The second era saw the decline of Echinoderms rod and the thrust of free forms. Ammonites abound and reach their peak. Trilobites and the Mérostomes disappear first leaving vestiges of their splendor. Crustaceans higher decapods, are emerging and insects complete metamorphosis to date Secondary. Fish bone skeleton well ossified cartilage replace (Ganoid). Reptiles know an amazing wealth of giant forms and populate the land as well as sea and air.
The first mammals, related to Ictidosauriens are known Jurassic: they are small and archaic complexion. The Placental only come later in the Cretaceous. Older birds have been found in the Upper Jurassic.
When the Tertiary opens all Reptiles giants have disappeared by contrast, birds and mammals experiencing extraordinary flowering. Almost all of their current orders form early this time.
Quaternary, Human, Homo sapiens, preceded by great Primates of Tertiary age, made its debut on the earthly scene.
After this very brief review, we find that the evolutionary order, that is to say, the chronological order of appearance of the groups is the order of anatomical and physiological complications such as zoologists have established. This ensures that simple shapes are older than the complex (the caveat regressive phenomena).
So far, no paleontological discovery came not invalidate this rule before the Agnathes Pisces, and the latter, the amphibians ... If we discovered a mammal prior to Reptiles, one would question the value of the law, but given the mass of material accumulated, it is safe to hold such an event is highly unlikely.
Complication organic and climb to a higher psychism does not oppose the diversification of types and specific developments forming the peaks of the mountains evoked in imagination all the forms that have succeeded in the evolution. Insect type (with social insects), the Decapod crustaceans, echinoderms ... highs are diversifying evolution. Man occupies one of them, but not the top of the pyramid (as stated anthropocentric conception of the universe) that would form the entire animal kingdom.
In many cases, the fossils have helped restore and follow the time evolution of lines, such as those of horses, the mastodons, Rhinoceros, Camels, to stick to mammals. Paleontology is more. She sometimes manages to surprise birth of a class. For example, it has established the genealogy of Mammals taking root in Reptiles Pélycosauriens. Their genesis was slow and extends over a period of about 80 million years.
Paleontologist also has a series of fossils (sea urchins, scallops, Cérithes ...) who taught him how to have it made news and irrefutable evidence of evolution. If, in spite of the evidence, we refuse this evidence, it denies any significance to fossils and is resigned to not understand or changes over time in plants and animals, or the appearance of new structures and new functions.
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- chemical composition unit:
Biochemistry has shown that all living things are composed of cytoplasm and one or more molecules of deoxyribonucleic acid (DNA) that encodes the information and ensure its replication, and its equal distribution, both quantitative and qualitative, is operated by equational mitosis. Electron microscopy demonstrated that all living beings have the same cellular organelles, namely kernel chromosomes and nucleolus, mitochondria, rough endoplasmic reticulum, Golgi apparatus, ribosomes. In addition, biochemistry showed that twenty amino acids formed protein structures of all living beings, as twenty-five letters were enough to give all the Indo-European languages.
These facts and others that we can not explain by lack of space, the idea of imposing the single origin of all living beings. The first substance is transmitted without interruption until we and perpetuated for centuries centuries, probably as long as our planet receive sunlight.
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embryological evidences:
The comparative study revealed embryogenèses facts demonstrating the existence of the evolutionary process. During its development the animal passes quickly through the embryonic state of his ancestors. This finding, Ernst Haeckel (1866) drew the fundamental biogenetic law, Thomas Huxley formulated with spirit form as follows: any animal during its embryonic development rises to his family tree. This law had been interviewed before by E. Haeckel R. Serres (1824) and von Baer (1792-1876), but neither one nor the other had understood the meaning-change.
Remember that the law is fully applicable to Mammals: during their ontogeny, they are first morula, blastula and gastrula then that deforms a wide lécithocèle (cavity filled with a liquid nutrient). Neurula their singularly reminiscent of those of Amphibians and Reptiles, gill slits and gill arches are recognizable and there, but the slots do not open, and the cellular material form that participates in the construction of the neck and the genesis of glands endocrine (thyroid, parathyroid, thymus). The outline of the heart is tubular and curved S as a Poisson heart, the kidney is primarily a pronephros, mesonephros and then finally a metanephros. All embryos of vertebrates have the notochord of Amphioxus and Agnathes; mold around her vertebrae.
These facts are unintelligible if we do not recognize a kinship, a common origin for animals during their embryonic development, have the same organic and drafts go through the same stages.
The fundamental biogenetic law applies to all branches, all component classes of the animal kingdom. It has been criticized by some naturalists including Anglo-Saxon stand Garstang (1923-1929) and Beer (1929). They oppose him as the embryo of a higher class like during its development, not to adults of the lower classes, but the embryos of these classes. It then replaces the law of Haeckel laws qu'énonça embryologist von Baer, there are more than a century, and the author does not live reports with evolution.
- During embryonic development, the general characters appear before the special character. A dog during its ontogeny, a vertebrate before a Mammal a Mammal and before being a carnivore.
- The less general structures derived from the most general structures and so on until the characters realize is the most special.
- The embryo of a given animal embryos remains distinct from other forms.
- Basically, the embryo of a higher animal never looks like an adult to an inferior species but only the embryo of the adult.
In fact, contrary to what some people believe biologists thought Haeckel is not so different from that of Von Baer. It is an insult to the naturalist Jena assume that an embryo capable of assimilating Mammal adult eating a fish, swimming and reproducing. Just make explicit criticism to show what is excessive. Haeckel held, it is certain to emphasize the persistence in individual development, traces of the previous state. He was right. It should not be that critical, with most of the detail on the bottom, do forget the merits of this penetrating view. Without doubt, larval or embryonic forms features that do not always have a clear relationship with adulthood earlier. So who affirm that the nauplii of crustaceans and annelid trochophore of a mollusc or correspond to ancestral adult forms rather than stages adapted to the dissemination of the species?
Moreover, Haeckel himself has seen the differences between ontogeny and phylogeny. It has separate structures that have a value phyletic those who do not. He never argued that the ancestors of the Dogfish (selachian) had swam with a huge yolk pendant their ventral surface. He described palingénétiques characters that summarize the ancestral stages and cœnogénétiques who appear secondarily. The placenta is an organ cœnogénétique, while the heart curved S, notochord, somites are cephalic palingénétiques. He also plainly seen that ontogeny may present character corruption palingénétiques by derangement of their order of appearance, in this disorder, it gives the name of heterochrony. In truth, the causes are multiple, during development, disturb palingenesis.
The embryo of a higher class like embryos or adults of the lower classes, it does not bear the imprint of the past less. Without it, who could recognize the systematic position and significance of rhizocephalan? Who would have guessed in a structure or Sacculina Peltogaster the organizational plan of arthropods? Person, no doubt! The discovery of nauplius and cypris embryonic stages not only allowed to say that Sacculina and Peltogaster are crustaceans, but clear affinities with the Cirripedia. The persistence of certain primitive stages here. In general, the parasitic organisms remain the most degraded larvae almost identical to those of the free species, include the nauplii of Xenocœloma this strange copepod that lives on the slopes of a grafted Annelida, Gastropoda trochophores the parasites. This applies to fixed forms: in the case of ascidians, for example, the larva "tadpole", which has notochord and neural tube, is an excellent example.
Gametes, embryos and larvae are less likely to vary than perfect forms. The sperm of all metazoans is built on the same type in the sponge as in the mammal, it is a flagellated cell without cytoplasm with a nucleus with a centrosome at its base. The spermatozoa aflagellées (various Crustaceans, Termites, Diplopoda, Arachnids ...) are only aberrations of general type. The interpretation of the persistence and consistency of this type can not be an evolutionist and oriented in the direction indicated by Ernst Haeckel. If the similarity is not interested adults but for the embryo, it does not change the substance of the law, in fact, the embryo carries the characters of the class to which it belongs, a finding that even the subject of the third law of Von Baer. Mammal that passes through the fish stage or the stage embryo fish, whatever the evolutionist! The key is that the influence continues to weigh on ancestral ontogeny.
How can it be spent on developing individual current process excellence? We must first realize that the embryonic organs, even if they do not give any part of the adult, however, are not devoid of function. The notochord, which is the only skeletal axis of Amphioxus and also, very nearly, the lamprey (agnathan) exists in the embryos of other classes of chordates, although in some it disappears completely at adults. It does not serve at least all mold and vertebral inductor: no notochord, no spine possible. Gill arches exist in all vertebrate embryos. In the adult stage, there are functional only in Agnathes and Pisces, but the amphibians to mammals, they play an important role in the genesis of certain parts of the respiratory system (Eustachian tube), lymphoid organs (tonsil, thymus) and cervical region. In other words, the same cellular material, according to the groups considered, and one for various productions. Here is an example: Meckel's cartilage, in mammals, a fate different from that suffered in other vertebrates, since all the bones from its proximal portions of the mandible separate and go in the service of middle ear. In the genesis of kidney, pronephros is probably organizer towards the mesonephros and the latter towards the metanephros. We must therefore take the utmost account of the embryonic physiology in interpreting ontogenetic structures.
However, there are bodies that are probably no function and are the remains of an ancestral condition: include, among others, the tooth germs Bird embryos, homologous teeth of the reptilian ancestor, vesicles coelomic head of the embryo Insect which disintegrate without a trace but indicate metamerism very distant ancestors (see paragraph on rudimentary organs).
All vertebrates, to stick to them, in their gene pool, a pool of genes that determine the structure "vertebrate", while other genes perform less general structure "bird", for example; finally, some depend on the characteristics of the order, genus and species. These genes during development, do not act at the same time, but come into action in a specific order. Those which correspond to the most general structures, that is to say, the oldest respond first and so on. The time lags of the activity of different genes are responsible for heterochrony. The genetic code is transmitted to the effectors in a defined temporal order, probably due to epigenetic development.
Phylogenetic recapitulation ultimately boils down to the possession of a variety of genes inherited from ancestors common to all classes below the class of the species. Nothing metaphysical, in this recall the past, but simply put into play under the influence of current causes, determinants inherited from more distant ancestors. Viewed in this light, the biogenetic law retains a value of the first order. It is also confirmed by other evidence embryological. And territories formative sheets and organs of vertebrates are arranged in the egg on a plane that is broadly in the tunicate egg ancestor of chordates (Amphioxus, Vertebrata).
Biochemistry has shown that all living things are composed of cytoplasm and one or more molecules of deoxyribonucleic acid (DNA) that encodes the information and ensure its replication, and its equal distribution, both quantitative and qualitative, is operated by equational mitosis. Electron microscopy demonstrated that all living beings have the same cellular organelles, namely kernel chromosomes and nucleolus, mitochondria, rough endoplasmic reticulum, Golgi apparatus, ribosomes. In addition, biochemistry showed that twenty amino acids formed protein structures of all living beings, as twenty-five letters were enough to give all the Indo-European languages.
These facts and others that we can not explain by lack of space, the idea of imposing the single origin of all living beings. The first substance is transmitted without interruption until we and perpetuated for centuries centuries, probably as long as our planet receive sunlight.
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comparative anatomy:
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Homologous organs:
It was found that the organs, although different in structure and function, from a single cell material of the embryo. Such bodies are known counterparts: for example, the swim bladder of fish and vertebrate lung air. The embryonic material change destiny, it is the principle of evolutionary deviation shows somehow evolution in action, with the acquisition of new genes. The mouthparts of insects, so different from one order to another, the bones of the face and skull of vertebrates not be interpreted in the light of the principle of progressive deviation and homology organic. It is recognized that animals with homologous organs have in common a certain set of genes, but from a certain stage of embryogenesis, other genes specific to each class or each order, come into play and undertake the development of relevant bodies in a new way.
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Rudimentary organs:
Rudimentary organs shall not be interpreted only through evolution, they are in fact good evidence. They are homologous organs normally developed in zoological groups held for less advanced. Atrophied muscles of the auricle in man is the counterpart of the muscles, which in some lemurs, moves the same flag.
The transient embryonic organs are material evidence of a past. For example, embryos of insects are on the underside of their abdomen rudimentary appendages disappear before the end of embryogenesis, but remain more or less developed in Thysanura (sensu lato) adults. The embryo of Orvet (Reptile lizard) has drafts of legs, while the adult is totally legless.
Rudimentary organs, remnants of the anatomical state of the ancestors, are more common than is generally supposed. The Anatomy of Man offers a rich assortment: musculature of the outer ear (already mentioned), muscle coccygeal muscle counterpart caudal vermiform appendix of the cecum, caudal vertebrae, semilunar fold, rudiment of the eyelid nyctitante several mammals, hair system of the body, etc..
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