Various branches of biology, including taxonomy, physiology, evolution, etc. Important progress has been made, but the main branches that fundamentally change the biological outlook are genetics, biochemistry and microbiology. 1900 After Mendel's law was rediscovered, the study of genetics was combined with cytology, and then genetics was established. By the 1930s, genetics had been considered as a guiding theory for studying the inheritance of traits at individual and population levels. Therefore, genetics plays an important role in biology and even the whole science. Since zymase was extracted from biochemistry by 1877, the research on metabolism in organisms has made rapid progress, and the catabolic pathway in organisms was basically clear in the 1940s. At the same time, great progress has been made in the study of the properties and biological energy of enzymes. For protein, nucleic acid, sugar, fat and other basic substances of life, not only the basic components are clarified, but also the three-dimensional structure is explored. Microbiology not only continued to study molds and bacteria, but also clarified the nature of viruses and bacteriophages in the 1930s and 1940s. The development and interaction of these three branches laid the foundation for the emergence of molecular biology.
After World War II, biology made a qualitative leap. The discovery of the double helix structure of 1953 DNA marks the birth of molecular biology, and also marks that the exploration of biology has begun to enter the door to uncover the mysteries of life. Since then, the decoding of genetic code and the establishment of recombinant DNA technology have not only created molecular genetics, but also made outstanding achievements in oncology and immunology at the molecular level. There has also been a major breakthrough in neurobiology, especially in the study of the brain. It can be seen that biology in the 20th century not only directly affected the development of its branches, but also had and will continue to have a great impact on agriculture and medicine, and even on the budding industrial revolution. Historians of science generally believe that there has been a revolution in biological science since the 1950s. This revolution is not inferior to the physics revolution in the first 30 years of the 20th century in opening up new fields, influencing other sciences, and influencing society and people's thoughts.
With the rapid development of biology in the 20th century, with the strong support of the rapid development of social economy, the principles, methods and precision instruments of modern physical chemistry were applied rapidly and massively in biological research. In this way, the quantitative research of biology has gradually developed. As some physicists and mathematicians are attracted to explore the unknown areas of the mysteries of life, a new theoretical biology discipline has emerged. Theoretical biology is a branch subject that mainly uses mathematical, physical and chemical methods to study various life phenomena. The early representative works are Theoretical Biology by L.von Bertalanfi of Austria (Volume I 1932, Volume II1942); M. Beguene's Biological Thinking Method (1959), etc.
/kloc-biology developed mainly in European countries in the 0/9th century, especially in Britain, Germany and France. For example, Cambridge, Oxford and other universities with a long history and scientific foundation in Britain and the academic activities of the Royal Society; Universities such as Gottingen, Heidelberg and Berlin in Germany and biological laboratories affiliated to Caesar-William Institute; University of Paris, France, 1888 Pasteur Institute established in Paris, St. Petersburg University, Russia. This situation changed a lot in the 20th century. This is because: Europe is the main battlefield of two world wars; 1933 Hitler's fascist dictatorship ruled Germany and pursued a cruel anti-semitic racist policy. Forced a large number of Jewish and anti-fascist German scientists to emigrate, most of whom moved to the United States. Science in the United States developed rapidly after the Second World War, and then came from behind and became the development center of world science. The biological situation is basically the same. American biologists began to grow up gradually at the end of 19. After merging with a large number of immigrant biologists from European countries, especially Germany, in the 1930s and 1940s, by the end of the 20th century, American biology had been in a leading position in both quality and quantity. Of course, after 40 years of post-war recovery and development, the above-mentioned European countries are still in the forefront of the world in science and technology. Some countries in Asia and South America are also actively carrying out research in this field.
Below, we will only introduce the brief historical overview of several branches of disciplines that developed rapidly and had great influence in the 20th century.
With regard to the development of the research on the genetic law at the cellular level, the rediscovery of Mendel's law in 1900, H. de Fries of the Netherlands, C. E. Collens of Germany and E.von Cermak of Austria have successively rediscovered Mendel's genetic law, and consulted the original text of Plant Hybridization Experiment, which has been submerged in library literature for 35 years, and made it public again. Since then, G.J. Mendel's discovery has been highly praised. The genetic law he discovered is called Mendel's law, and he himself is also called the founder of modern genetics. The rediscovery of Mendel 1900 law marks the beginning of modern genetics. H. de Fries and C. E. Collens were both famous botanists at that time. They had a good understanding of plant hybridization and heredity, while E.von Cermak was a young plant breeder. The history of science generally speaks highly of the first two, especially Collen; But in any case, they are all based on their own work and fully realize the significance of Mendel's discovery. Collins once said, "rediscovery is far less than Mendel's original discovery, and its weight is much lighter." W batson, a British geneticist, immediately discovered Mendel's report and translated it into English at 190 1, thus promoting its wider spread in English-speaking countries.
In the years after the establishment of cytogenetics and the rediscovery of Mendel's law, biologists have carried out various experiments with many other animals and plants as materials, and the results show that Mendel's law is a genetic law that animals and plants generally follow. During the period of 1900 ~ 19 10, many important genetic concepts were established. 1902 ~ 1904, American cytologist W. S. Sutton and German cytologist T. H. Boveri both found that in the process of the formation and fertilization of male and female gametes, the behavior of chromosomes is parallel to the Mendel hypothesis, thus putting forward the theory that Mendel inheritance is based on chromosomes. W batson of Britain put forward the term genetics in 1906. As early as 1902, he put forward some important concepts such as heterozygote, homozygote and allele. H de Fries put forward the concept of "mutation". Danish biologist W.L. Johansen established the pure line theory in 1909, and put forward some terms and concepts such as "gene", "genotype" and "phenotype". From 190 1 ~ 1905, American cytologists C.E. McLean, E.B. Wilson and W.L. Stevens proved that there are two kinds of particles in animal nuclei: one contains a chromosome (or X chromosome); The other one didn't. People think that sex is determined by this extra chromosome. E.B. Wilson's Cell in Development and Genetics was first published in 1896, reprinted in 1900, and almost completely rewritten in the third edition of 1925, which played a positive role in promoting the development of cytogenetics.
From 19 10 to 1930s, the establishment of cytogenetics and the enrichment and development of Mendel's law were mainly attributed to the scientific contributions of American geneticist H. Morgan and his school. Morgan and Wilson are colleagues and close friends. He has Wilson's support from academic to administrative aspects. Morgan was not convinced of Mendel's law at first, on the one hand because of the prejudice of embryologists, and on the other hand because the genetic phenomena he observed were far more complicated than Mendel's law. However, on the basis of cytology and embryology, he conducted a large number of hybridization experiments with Drosophila as materials, and finally established cytogenetics or chromosome genetics. 19 10 years, he found that the white-eyed mutant of Drosophila is always a sex-linked genetic phenomenon related to males, and proved for the first time through experiments that the "gene" for genetic white-eyed is a substance located on the sex chromosome. Later, he and his collaborators, as well as geneticists from other units and countries, did a lot of systematic research on Drosophila. The research showed that different "genes" had "linkage" phenomenon in the genetic process, and there was "exchange" phenomenon between homologous chromosomes. A large number of their hybridization experiments have proved that genes have a fixed position on chromosomes. By observing the chromosome under the microscope and calculating a large number of experimental data, the relative positions of various genes on the chromosome are found (see linkage and exchange, gene mapping). 19 15 years, the publication of Mendel's Genetic Principles, co-authored by Morgan and young scholars in his laboratory, A.H. Sturtevant, H.J. Mahler and C.B. bridges, had a considerable influence in the academic circles. 1927, H.J. Mahler artificially induced mutation in Drosophila by X-rays, which was the first and most convincing example of artificially changing genes, and opened up broad prospects for genetic research and practical application. 1933, other scientists discovered the giant chromosomes of salivary gland cells. Later, in 1938, bridges drew a chromosome map of Drosophila, with nearly 4,000 genes. These works provide an important foundation for the establishment of gene theory.
T.H. Morgan revised the book Gene Theory published by 1928, and compared the position of genes in genetics with that of atoms and electrons in physics and chemistry, and held that: "Only when these theories can help us to make special numerical and quantitative predictions, they have the value of existence." This passage basically summarizes the achievements of genetics in the past 30 years. In the last paragraph, he raised the question that "genes belong to the level of organic molecules" and thought that "genes are stable because they represent an organic chemical entity. This is the simplest hypothesis that people can make now. Since this opinion is in line with known entities about gene stability, at least it is a good experimental hypothesis. " This prediction was confirmed in the later scientific development.
The Soviet Union and other countries once denied cytogenetics. At the time of the development of genetics, in the Soviet Union, an argument took place after the death of Michulin 1935, with agronomist lysenko on the one hand and botanist and geneticist ни vavilov on the other. Due to lysenko's political support, especially after the meeting of the All-Soviet Leninist Academy of Agricultural Sciences in August 1948, the genetic theories of G.J. Mendel, A.weismann and T.H. Morgan were completely denied, and they were labeled as "reactionary", "idealistic" and "metaphysical", and at the same time the relevant teaching and research work were ordered to stop. This situation did not return to normal until 1964. The criticism and negation in the past 30 years have changed the genetics and related disciplines in the Soviet Union from advanced to backward, and also affected many socialist countries including China.
Research progress of biomacromolecules and metabolic pathways in the early 20th century Understanding of biomacromolecules Biochemistry originated from the physiological chemistry of19th century and developed in the 20th century. At first, due to the research of animal and plant chemistry by some organic chemists, they began to understand the chemical composition and partial structure of protein, nucleic acid, sugar and fat, which are important substances that constitute life. It took scientists 100 years, and it was not until 1940 that all the 20 amino acids that make up protein were found out. 1At the end of the 9th century and the beginning of the 20th century, German chemists E. Fischer and F. Hoffmeister put forward the theory that protein's structure is a long chain of amino acids linked by peptide bonds, and pointed out that all natural amino acids are L series (levorotatory). However, it was not until 1929 that T. Svedbergh, a Swedish chemist, used his own ultracentrifuge to determine the macromolecular properties of protein. After J.F. Mischel discovered nucleic acid in 1869, German biochemist A. Causel and American and Russian biochemist P. A.T Levin systematically studied the structure of nucleic acid from the turn of the century to the 1930s, and found that nucleic acid was composed of four different nitrogen-containing heterocyclic compounds (purine and pyrimidine derivatives, commonly known as bases) combined with ribose and phosphoric acid. In 1929, P. A.T Levin found that there are differences between deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) because the oxygen content of ribose is different. Due to the limitation of the conditions at that time, he mistakenly thought that the contents of four bases in nucleic acid were equal according to inaccurate determination, and put forward the wrong "tetranucleotide" hypothesis about the structure of nucleic acid in 192 1, which simplified the complex structure of nucleic acid. This hypothesis was generally accepted in 1930s, which influenced people to reveal the important function of nucleic acid as a living body. It was not until the mid-1940s that the genetic function of nucleic acid was affirmed, and the newly established accurate method was used to analyze it again, and it was found that the contents of the four bases were not completely equal. This overturns the hypothesis of "four nucleotides" and is helpful to the establishment of DNA double helix structure model in the future.
The properties of basic metabolic pathways, enzymes and bioenergy are complex. In the first half of the 20th century, the catabolic pathways of sugar, fat and protein were basically clear.