What is Biological Classification?
Taxonomy is a basic method for studying organisms. Biological classification is mainly based on the similarity of organisms (including morphological structure and physiological functions), classifying organisms into different levels such as species and genera, and scientifically describing the morphological structure and physiological functions of each group. Understand the genetic and evolutionary relationships between different taxa.
Taxonomy
- Humans have long been able to identify and give names to objects. In the early Han Dynasty, Erya divided animals into four types: insects, fish, birds, and beasts: insects include most of them.
- Taxonomy
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- [Note: Three-domain system has been adopted internationally]
- People have classified organisms in different historical periods. From the perspective of historical development,
- Each level of units listed in the meta-system has a scientific name. The basic procedure of classification is to classify the research objects into a certain system and level and become the unit of the category. So classification and naming are inseparable.
- The scientific names of species and genera are often followed by the surname of the person to indicate the source and facilitate the search of the literature. The scientific name of the variant also adopts a three-name system. The classification name requires stability, and a genus or species (including sub-species units) can only have one scientific name. A scientific name 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". The earliest named object must be checked in it, and other objects with the same name have a new name. This is called the "priority law", and the taxonomy of animal and plant taxonomy has formulated its own "Nomenclature Regulations", so there is no problem of the same name between foreign animals and plants. "Priority law" is an important measure to stabilize scientific names. The date of the priority law was 1758 for animals, 1820 for plants, and 1 January 1980 for bacteria.
- Identification of scientific names is a means of obtaining species-related information. Even if it is a previously unknown new species, as long as its classification is identified, certain characteristics can be foreseen. Classification systems are retrieval systems and information access systems. Many classified works, such as flora and fauna based on flora surveys, describe the animal and plant species of a certain country or region as basic information, and serve for identification and investigation.
- A species refers to an animal or plant group. All members are so similar in morphology that they can be considered as the same organisms with small variations. Each member of them can normally mate and breed reproductive offspring. Species It is the basic unit of biological classification and the basic unit of biological reproduction.
- The concept of species reflects the ideological trend of the times. In the Linnaeus era, people believed that species were immutable and that the same individuals conformed to the same "pattern". The concept of pattern originates from the ancient concept of ancient Greek philosophy, and is applied to the entire classification system. The concept assumes that all kinds of unit units in all levels of the meta-system are in accordance with a pattern.
- The change and invariance of species used to be the focus of the struggle between evolution and creationism. However, the facts of taxonomy show that each species has its own characteristics, and no two species are exactly the same; and each species maintains a series of ancestral characteristics, which can determine its boundaries, gates, outlines, families, genera, etc. Classification status and reflects its evolutionary history.
- The basic content of classification work is to distinguish species from natural species, the former is species-level and sub-species classification, and the latter is on-species classification. The concept of population has improved the level of species-level classification and improved sub-species classification. The main point is to replace sub-species with variants. Subspecies generally refers to geographical subspecies, which is the geographical differentiation of populations, and has certain distinguishing characteristics and distribution ranges. The subspecies classification reflects species differentiation and highlights the spatial concept of species.
- The term variant was used in the past, some referring to individual variation and some referring to the type of group. The meaning is very ambiguous and has been abolished in animal classification. In plant classification, it is generally used to distinguish discontinuous variants within populations. Ecotype is an in-species type that lives in a certain habitat and has certain ecological characteristics, and is often used for plant classification. The sub-units of artificially selected plants and animals are called varieties.
- Due to the complexity of intra- and inter-species variation, taxonomists sometimes differ greatly in the classification of species. Morphological species are classified according to the similarities and differences of external forms as the basis for classifying species. Due to the different understanding of the importance of various morphological features, the classified species differ from person to person, especially the classification scholars' "Weighting" often makes them more important than other characteristics, and creates subjective bias.
- A species or species, as well as the entire plant and animal world, has its own history. The study of phylogeny is to explore the historical origins between species in order to clarify kinship and provide theoretical basis for classification. Although there are three major schools of classification (evolutionary) taxonomy, branch systems, and numerical taxonomy in the taxonomic school, they all have a lot in common in their basic principles, but each emphasizes different aspects.
- Feature comparison is the basic method of classification. The so-called contrast is the comparison of similarities and differences: "different" is the basis for distinguishing categories, and "same" is the basis for merging categories. To analyze classification characteristics, we must first consider common characteristics that reflect common origins. But there are differences between homologous and non-homologous. For example, the wings of birds and the forelimbs of mammals are homologous tubes, which can be traced back to the common ancestor, and are "homologous characteristics". The constant temperature in birds and beasts is of different origins, not from common ancestors, and is a "non-homologous feature". Systematic classification uses homologous characteristics, and does not take non-homologous traits.
- Lin Nai divides living things into two major groups: fixed 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 followed by general textbooks and remained basically unchanged.
- The initial problems arise from intermediate types. For example, the eyeworm combines the dual characteristics of both animal and plant kingdoms. It has chloroplasts for photosynthesis, and can act and ingest food. Botanists have classified them as algae, called Euglena; zoologists have classified them as protozoa, known as eyeworms. The intermediate type is evidence of evolution, but it becomes a classification problem.
- In order to solve this problem, in the 1860s, it was proposed to establish a third realm composed of lower organisms, named the protozoa, including bacteria, algae, fungi and protozoa. This three-world system solved the problem of indistinguishable animal and plant boundaries, but it was not accepted. It took a full 100 years until the 1950s before it became popular for some textbooks. Has been used today.