By the 1930s of 19, it had been noticed that the plant kingdom and the animal kingdom had certain structural consistency, both of which were composed of cells, and they also had a considerable understanding of the structure and life of single-celled organisms. Under this background, German botanist Schleiden put forward the main argument of cell theory in 1838. The following year, Wang Shi put forward that "all animals are also made of cells", which supplemented Schleiden's view that "all plants are made of cells". This is the basis of cell theory. Twenty years later, another German scientist, RudolfVirchow, came to another important conclusion: all cells must come from existing living cells. At this point, the research results of the above three scientists, together with the discoveries of many other scientists, have formed a relatively complete cell theory.
The cell theory was first put forward by German MatthiasJakobSchleiden and zoologist Wang Shi from 1838 to 1839, and it was not perfected until 1858. This is a theory about biological composition.
Significance: Cell theory demonstrates the structural unity and evolutionary homology of the whole biological world. Cell theory reveals the unity of cells. The establishment of this theory has promoted the development of biology and provided an important natural science foundation for dialectical materialism. Engels, the revolutionary mentor, once praised the cell theory, the law of energy conservation and transformation, and Darwin's theory of natural selection as one of the most important natural scientific discoveries in the19th century.
Main contents:
1. Cells are organisms, and all animals and plants are developed from cells and composed of cells and cell products (it cannot be described as "all living things are composed of cells and cell products"), because viruses are not composed of cells. 1886, Meyer, a German working in the Netherlands, crushed the leaves of tobacco plants with mosaic disease with water and injected the juice into healthy tobacco. Through the analysis of leaves and soil, Meyer pointed out that tobacco mosaic was caused by bacteria. ); 2. All cells are basically similar in structure and composition; 3. The new cell is derived from the existing cell; 4. Biological diseases are due to the dysfunction of its cells; 5. Cell is the basic unit of organism structure and function; 6. Organisms reflect their functions through the activities of cells; 7. A cell is a relatively independent unit, which has its own life and plays a role in the whole life composed of other cells.
Biological evolution, or evolution for short, is one of the most basic theories in biology.
The idea of modern biological evolution began to sprout in the middle of18th century. /kloc-before the middle of the 0 th/8 th century, people were bound by religious theology or metaphysical world outlook, and it was generally believed that species were unchangeable. /kloc-after the middle of the 0/8th century, with the development of geology, comparative anatomy and embryology, the viewpoint of biological species evolution was put forward. However, it took 100 years from the germination of evolutionary thought to the establishment of Darwin's theory of evolution.
Buffon, a French scientist, is one of the pioneers of evolution and has published many views on evolution. In Natural History, he tried to describe a complete history of natural development and a realistic natural picture from the living and abiotic periods of stars, the solar system to the earth, and then to the earth. Buffon believes that species are changeable, and the reason of biological variation lies in the change of environment. When the environment changes, organisms will undergo corresponding variations, which will be passed on to future generations.
On the basis of studying animals and fossils, Lamarck, a French scientist, thinks that today's organisms evolved from ancient organisms, and puts forward theories such as "use into waste" and "acquired inheritance". Lamarck's theory of evolution is the pinnacle of the development of French evolutionary thought. However, his theory of evolution was not widely accepted at that time, not only because he could not produce more facts to prove his theory, but also because he met a powerful opponent-giant.
1859165438+10 In October, the British naturalist Darwin published The Origin of Species, in which he established an epoch-making theory of evolution. In the Origin of Species, Darwin systematically expounded his evolutionism with a lot of rich materials. The publication of the Origin of Species has caused a heated debate, especially the struggle between evolution and religious circles. 1860 On June 28th, planned by the church and some conservative scientists, the British Science Association held a three-day seminar at Oxford University, which was called to discuss Darwin's theory, but actually attacked evolution. This debate ended in the failure of church creationism and the victory of evolution.
Darwin's theory of biological evolution can be summarized as: 1 Biology is evolutionary, neither created by God nor immutable. 2. Variation is a common phenomenon in biology, and the basic reason for variation is the change of living conditions. 3. New species can be produced by artificial cultivation. 4. Similar creatures originated from a common ancestor, and the ultimate origin of loyal creatures is single. 5. In nature, biological species are produced by natural selection; Natural selection is realized through struggle for existence; The result of survival competition is "natural selection, survival of the fittest", which is the basic law of biological evolution. Darwin's struggle for existence includes intraspecific struggle, interspecific struggle and natural environment struggle. 6. Darwin also believed that organisms not only have variation, but also have heredity, which not only ensures the reproduction of species, but also ensures that favorable variation is passed on to future generations. Beneficial variation is gradually accumulated from generation to generation, and finally new species can be produced. In a word, Darwin gave a regular explanation for biological evolution. Darwin's theory of evolution holds that biological variation, heredity and natural selection can lead to adaptive changes of organisms from the perspective of the interaction between organisms and the environment. Because it is based on sufficient scientific facts and can stand the test of time, it has had a far-reaching influence in academic circles for more than one hundred years.
There are three classical evidences of evolution: comparative anatomy, paleontology and the law of embryo development recurrence.
Deficiency: 1 is lack of transitional fossils; 2 is the age of the earth; Three difficulties are the most fatal: Darwin could not find a reasonable genetic mechanism to explain natural selection.
Supplement: Neo-Darwinism came into being at the end of 19 and was founded by German biologist weismann. American geneticist T.H. Morgan and British geneticist J.A. Thomson are also influential neo-Darwinists. 1896, G.J. Romanes called this theory "neo-Darwinism" for the first time. Mendel, the father of modern genetics, discovered the laws of inheritance, separation and free combination through pea experiments.
Before Mendel, there was no clear scientific explanation for the genetic phenomenon of children like their parents. Mendel laid a framework for the future theory of genetic factors, and this discovery is of historic significance. Unfortunately, before Mendel's death, this discovery did not get enough attention. However, it was not completely buried. The Encyclopedia Britannica 188 1 has introduced Mendel's research. Mendel discovered the law of independent distribution through pea experiment. Mendel crossed the seeds with many traits such as pea height, short stem, wrinkle or not, and found that the genetic mode of each trait of seeds did not affect each other, and each trait conformed to the dominance principle and separation phenomenon, which was called the law of independent distribution. It is also worth mentioning that after Mendel's death, people found that this law can only be established under certain conditions.
Weismann
Weismann distinguished germplasm (germ cells) from physique (somatic cells, such as nerve cells and muscle cells) for the first time, emphasizing that germplasm plays a reproductive and genetic role, has stability and continuity, and can be passed down from generation to generation; However, constitution can only reproduce itself, producing the same cells as nature, and its function is to engage in various nutritional activities. This theory has promoted the development of biology to some extent. Main representative works: Germplasm Theory and Lecture on Evolution.
In 1892, weismann put forward the theory of germplasm continuity by studying the evolution of flies, the reproductive behavior of Daphnia and the influence of tail cutting on heredity. Basic viewpoint: 1. Biology is composed of germplasm and constitution, and inheritance must pass through germplasm, which has nothing to do with constitution; Acquired traits are physiological changes and cannot be inherited. 2. He thinks that natural selection is the only mechanism of evolution, and the object of natural selection is germplasm.
Evolution in different periods and the outline of evolution