Classification system is a hierarchical system, which usually includes seven main levels: species, genera, families, orders, classes, phylum and boundary. Species (species) are the basic units, related species, related genera, families, genera, orders, orders, classes, phylum and phylum.
With the deepening of research, the classification level is getting higher and higher, and sub-units can be attached to the upper and lower units, such as superfamily, subclass, superfamily, suborder, next day, superfamily, subfamily and so on. In addition, you can add new companies, such as stocks, groups, families, groups and so on. Among them, the most permanent is the family, which is between subfamily and genus.
All units listed in the hierarchy have a scientific name. The basic procedure of classification is to classify the research object into a certain system and level and become a class unit. So classification and naming are inseparable.
The scientific names of species and genera are often accompanied by the names of people's names to show their origins and facilitate the search for documents. The scientific name of the variety also adopts the three-name system, and the classification name requires stability. A genus or species (including subspecies) can only have one scientific name. Scientific names can only be used for one object (or species). If there are two or more objects, it is a "foreign object with the same name", in which the earliest named object must be approved, and other objects with the same name will be given new names. This is called the "priority rule", and the taxonomy of animals and plants has formulated its own naming regulations, so there is no problem of foreign bodies with the same name between the animal kingdom and the plant kingdom. "Priority method" is an important measure to stabilize scientific names. The starting date of priority method is 1758 for animals, 1820 for plants and 1980 for bacteria.
Scientific name identification is a means to obtain species information. Even if it is a new species that was unknown before, as long as its classification and affiliation are identified, some characteristics can be predicted. Classification system is not only a retrieval system, but also an information acquisition system. Many classified works, such as Animals and Plants Based on Floristic Investigation, describe the animal and plant species of a country or region as basic data, and all serve for identification and retrieval.
A species refers to a group of animals or plants, and all its members are very similar in morphology, which can be considered as the same organism, with little variation, and each member can mate normally and reproduce. Species are the basic units of biological classification and reproduction.
The concept of species reflects the ideological trend of the times. In the Linnaeus era, people thought that species were immutable, and individuals of the same species conformed to the same "pattern". The concept of pattern comes from the ancient concept of ancient Greek philosophy and is applied to the whole classification system. This concept assumes that all class units in all ordered element systems conform to a pattern.
The change and invariance of species used to be the focus of the struggle between evolution and creationism, and it was an irreconcilable view. But taxonomic facts show that each species has its own characteristics, and no two species are exactly the same; Each species maintains a series of ancestral characteristics, which can determine the taxonomic status of its boundary, phylum, class, family and genus and reflect its evolutionary history.
The basic content of classification is to distinguish species from genera. The former is the classification of species and subspecies, while the latter is the classification of species. The concept of population improves the level of species classification and subspecies classification, and its main point is to replace varieties with subspecies. Subspecies generally refers to geographical subspecies, which is the geographical differentiation of population and has certain distinguishing characteristics and distribution range. Subspecies classification reflects species differentiation and highlights the spatial concept of species.
In the past, the word variation was used in various ways, some referring to individual variation, some referring to group type, and its meaning was unclear, so it has been abolished in animal classification. In plant classification, it is generally used to distinguish discontinuous varieties within a population. Ecotype is an intraspecific type that lives in a certain habitat and has certain ecological characteristics, and is often used for plant classification. The artificially selected subspecies of plants and animals are called varieties.
Because of the complexity of intraspecific and interspecific variation, taxonomists sometimes have great differences in species division. Species are classified according to the similarity and difference of external morphology, which is called morphological species. Because of the different understanding of the importance of various morphological features, the classified species vary from person to person, especially the "weighting" of some features by taxonomists often makes them more important than others, thus resulting in subjective prejudice.
A species or thing, even the whole plant and animal kingdom, has its own history. The purpose of studying phylogeny is to explore the historical origin of species, clarify the genetic relationship and provide theoretical basis for classification. Although there are three schools of taxonomy: comprehensive (evolutionary) taxonomy, cladistic systematics and numerical taxonomy, their basic principles have many similarities, but each has its own emphasis.
Feature comparison is the basic method of classification. The so-called comparison is the comparison of similarities and differences: "difference" is the basis for distinguishing categories, and "similarity" is the basis for merging categories. To analyze the classification characteristics, we should first consider the identity characteristics of * * * which reflect the origin of * * *. But there are differences between homologous and non-homologous. For example, the wings of birds and the forelimbs of mammals are homologous organs, which can be traced back to the same ancestor. It is a "homologous feature" that constant temperature is a separate origin in animals and birds, not from the same ancestor, but a "non-homologous feature". Systematic classification adopts homologous characters, not non-homologous characters.
Linnaeus divided living things into two categories: stationary plants and moving animals. Over the past two hundred years, with the development of science, people have gradually discovered that there are many problems in this two-world system, but until the 1950s, it was still used by general teaching subjects and remained basically unchanged.
The initial problem arises from the intermediate type, such as the euglena, which combines the dual characteristics of the animal and plant worlds, not only has chloroplasts for photosynthesis, but also can move and ingest food. Botanists classify them as algae, called gymnosperms; Zoologists classify them as protozoa, called euglena. Intermediate type is the evidence of evolution, but it has become a difficult problem of classification.
In order to solve this problem, in the 1960s of 19, it was proposed to establish a third world composed of lower organisms, named protozoa, including bacteria, algae, fungi and protozoa. This three-boundary system solves the problem that the boundary between animals and plants is difficult to distinguish, but it is not accepted. It was 100 years before it became popular for a while and was adopted by many textbooks.
The history of life has gone through several important stages. The first life should be a cell-free life. Of course, there must be an "acellular" or "precellular" stage before cells appear. Virus is a cell-free organism, but its origin, whether it is primary or secondary, is still inconclusive.
From cell-free to cell-free is the second important stage of biological development. Early cells are prokaryotic cells, and early organisms are called prokaryotes (seedlings and cyanobacteria). Prokaryotic cells are simple in structure; No nuclear membrane, no complicated organelles.
From prokaryote to eukaryote is the third important stage of biological development. Eukaryotic cells have a nuclear membrane, and the whole cell is divided into two parts: nucleus and cytoplasm: the nucleus has complex chromosome devices and becomes the genetic center; Cytoplasm has a complex organelle structure and becomes a metabolic center. Eukaryotic cells differentiated from nucleoplasm have much higher body level than prokaryotic cells.
From unicellular eukaryote to multicellular organism is the fourth important stage in life history. With the appearance of multicellular graphics, complex tissue structures and organ systems have been developed, and finally advanced angiosperms and mammals have been produced.
Plants, fungi and animals constitute three links of the ecosystem. Green plants are autotrophs and producers of nature. They use chlorophyll for photosynthesis to synthesize organic nutrients from inorganic substances and supply them to themselves and heterotrophs. The fungus is heterotrophs, a decomposer of nature. They get food from plants, break down organic food into inorganic substances, and in turn provide raw materials for plants. Animals are also heterotrophs. They are consumers and the last creature on earth.
Even without animals, plants and fungi can still exist, because they already have two basic links in the natural material cycle and can complete the system of synthesis and decomposition in the cycle. However, if there were no animals, the biological world would not be so colorful, let alone human beings. Plants, fungi and animals represent three routes or directions of biological evolution.
At present, the most popular classification is the five-boundary system. The system of five realms reflects three stages of biological evolution and three branches of multicellular stage, with vertical and horizontal classification. It does not include non-cellular viruses, perhaps because the state of the virus system is unknown. Its protozoan world is complex, including all protozoans and other eukaryotic algae except red algae, brown algae and green algae, including different animals and plants.
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