Specific:
1 Variation of genetic material is the internal cause of evolution.
There are hundreds of millions of species in nature, with various forms and species, and the biodiversity is mainly caused by different genetic materials. The relative stability of the genetic material of the same species ensures the stability and continuity of this species. The variation of genetic material provides the possibility for biological evolution.
1. 1 Gene mutation and chromosome aberration
After the quantitative analysis of biological macromolecules, the neutral theory holds that genes will produce a large number of neutral mutations at any time. For the structural gene encoding protein, when 1 nucleotide (especially the third position) in the triplet code is replaced, the amino acid type often remains unchanged. Protein's conservative substitution also pointed out that even if a single amino acid residue changes, the residue is still in the variable region, and this change does not affect the survival value of life. In addition, structural genes are only a small part of the whole DNA sequence, and there are many sequences that do not encode protein, such as regulatory genes, repetitive sequences, introns, pseudogenes, degenerate genes and so on. Therefore, Gen Kimura and others concluded that the dominant factors of biological evolution at the molecular level are those "neutral" genes that are neither beneficial nor harmful to biological survival. But how to define "absolute" neutral mutation is still a complicated problem. Non-coding protein genes such as regulatory genes, introns, repetitive genes and pseudogenes do not directly guide the synthesis of protein, but combine with various environmental factors to play a role by regulating the process of transcription and translation. Studies have shown that the change from apes to humans is mainly the change of regulatory genes, not the change of structural genes [1]. Many experimental evidences also support Gilbert's hypothesis about intron function, and think that structural genes are produced by exon combination through recombination between intron sequences, that is, introns are the residues of the original gene recombination process. In addition, as far as people know, introns also have the function of regulating gene expression; Regulate RNA splicing; Encoding a specific protein; Protect gene families and other functions [2]. Both rRNA and tRNA are repetitive genes and have their own functions in protein's translation. Pseudogenes can obtain functions by accepting fragments of adjacent functional genes or moving functional genes. Examples of exon exchange between pseudogenes and functional genes have been found in mice ψ a3 [3]. Some single nucleotides may not be able to change the types of amino acids after being substituted, but their influence on adjacent nucleotides through chemical bonds can not be ignored. It can change the substitution rate of adjacent nucleotides. Therefore, I think it is inappropriate to define some gene mutations as absolutely neutral.
Chromosome aberration includes changes in chromosome structure and quantity, which plays an important role in evolution as well as gene mutation. Chromosome aberration involves the extensive changes of DNA molecules, affects the linkage and exchange between genes, changes the expression mode of genes, produces reproductive isolation mechanism and accelerates the process of species differentiation.
1.2 gene recombination
It is difficult to explain the evolution of virus by gradual mutation accumulation, and the jumping mutation caused by gene recombination between virus and host or other viruses plays a great role [4]. In fact, the frequency of gene recombination caused by transformation, conjugation and transduction between microorganisms is ten thousand times higher than that of gene mutation [5]. Therefore, gene recombination is the main way of virus and microorganism evolution. For higher organisms, exogenous nucleic acids can also be obtained through feeding, sexual reproduction and microbial mediation, providing necessary material elements for gene recombination. Zhang Guangming et al. [6] proposed that microorganisms can effectively mediate gene recombination, and extensive translocation from prokaryotes to eukaryotes may be an important way of microbial-mediated gene recombination. Microorganisms first infect one organism and carry its genetic material, then infect another organism and transfer the genetic material to the genome of another organism. Because another organism itself has a perfect and stable genetic mechanism, the probability of this gene recombination being expressed and fixed is not great, but it is undeniable that gene recombination plays an important role in biological evolution.
2. The induction and screening effect of environment on genetic material variation
From the ecological point of view, any living thing exists in a stable and constantly changing ecological environment, and there is an exchange of material, energy and information with the environment. Environment is the external cause of biological evolution, which induces genetic material to mutate and screen it, and realizes biological evolution through time accumulation. The environment here includes biological environment and abiotic environment, and macro environment and micro environment refer to all external factors that have an impact on the research subject.
2. 1 Environmental-induced genetic material variation
As far as the chemical environment is concerned, organisms absorb various substances from the environment, decompose and absorb them and send them into cells. Some chemical components and elements in these substances may react with the composition of genetic material or change the structure of genetic material. Some chemicals directly act on the surface of organisms, which may also cause the destruction of surface cells and make genetic material mutate.
The most important factor that the physical environment can cause genetic material variation is radiation. Living on the earth, creatures are constantly radiated by cosmic rays and radioactive substances on the earth. Scientists have done statistics, and the radiation that a person receives in the human body on average every year can open chemical bonds of about one billion molecules. The proportion of DNA molecules in human body is very small. The result of calculation is that each person will destroy about 200 DNA molecules every year on average [7]. If an organism is accidentally exposed to higher energy rays, it is more likely to cause mutation.
Nowadays, many scientists use genetic engineering technology to artificially change some fragments of DNA and cultivate new varieties that are beneficial to production economy. If transgenic animals, plants and microorganisms are popularized, it will provide certain material possibilities for the evolution of this organism. The hybridization between new varieties and related wild species may spread and fix artificially modified gene fragments. This is more common in plants. It can also be said that this is the influence of man-made environment on biological evolution. Microbial-mediated gene recombination makes organisms evolve, and natural biological environment changes genetic material.
Whether acquired traits can be inherited has always been the focus of debate in the study of biological evolution. If the obtained traits are heritable, it can be further explained that the environment can cause genetic material variation. Biologists have found many examples of acquired inheritance. For example, after the cell wall of Bacillus subtilis is removed by an enzyme, they can continue to reproduce under certain growth conditions, and their offspring are borderless, which can be inherited stably. Only when they are placed in another growth condition will the cell wall grow again [8]. The discovery of reverse transcriptase also confirmed the possibility of genetic acquisition. Scholars of "life-environment balance theory" believe that if the environmental conditions of life change, life will change, then animals and plants will adopt traits that adapt to their lives, and in the case that this trait exists forever, genetic factors will change accordingly. But it must go through such a long time unit as geological age. More and more evidence proves that possessiveness can be inherited, but it cannot be considered as the main way of biological evolution. Because the pace of biological evolution has not completely stopped for a long time without great changes in environmental conditions. Biological evolution is the result of many factors, in the final analysis, genetic material must have changed, and only in this way can variation be passed down from generation to generation. Environment can only be the external cause of evolution.
In addition, some scientists believe that most mutations are spontaneous and completely random, which is not comprehensive. The DNA chain is in the cell, so it must live in the intracellular environment. The shedding, substitution and addition of amino acid residues are accompanied by the cleavage of peptide bonds, which requires the exchange of energy and substances, and these changes are closely related to the intracellular environment.
2.2 Environmental screening of genetic material
At the molecular level, the environment plays a constructive role in the natural selection of genetic material. One site on the DNA chain is surrounded by other gene sites. If this site mutates, it will be constrained and interfered by other genes around this site. In addition, it is also regulated by various chemicals in the nuclear environment and histones (only eukaryotes) and non-histones on chromosomes. In short, in the early stage of new genotype evolution, favorable mutations will be selected to improve individual fitness. Ota of Japan (Ohta, 1979) said that the main function of natural selection at the molecular level is to maintain the existing function of a molecule and protect it from harmful mutation [8].
When the variation of genetic material has passed natural selection at the molecular level, it must be tested at a higher level. No matter whether the mutation site on DNA directly guides protein synthesis or indirectly regulates and influences the process of transcription and translation, the variation of most genetic materials is ultimately reflected in the change of protein. The change of one or more amino acid residues in the polypeptide chain will affect the spatial conformation and function of protein. The principle of minimum energy is pursued when the peptide chain is folded, and the fully folded peptide chain should make its spatial conformation conducive to its better function. If the change of amino acid residues causes the change of protein's function, the function played by the changed protein will make the organism better adapt to the environment and improve its viability. These include natural selection at the cellular level and natural selection at the tissue and organ level related to protein's function. These selections will screen protein changes caused by genetic material variation.
When the variation of genetic material is finally manifested as phenotypic difference, the role of environment is similar to Darwin's theory of natural selection. Only according to modern biological evolution theory, the object of natural selection is not individual, but group. The value of natural selection lies in the change of gene frequency in population gene pool.
As mentioned earlier, some mutations seem to be neutral and meaningless. But when environmental conditions change, it is very likely that these mutations are no longer "neutral" [9]. These reserve mutations can only be shown when environmental conditions change. In recent years, experiments have shown that there are some molecular mechanisms represented by heat shock protein HSP90, which can hide the phenotypic changes caused by gene mutation to some extent [10]. In other words, the environment can choose some mutations, let them express, and let others temporarily hide. Through these hidden backup mutations, individuals have a greater chance to adapt to the changing environment.
3 biological response to the environment after evolution
About 2.7 billion years ago, primitive algae, such as flint algae and blue-green algae, appeared. They contain chlorophyll, can carry out photosynthesis and belong to autotrophic life. The oxygen released by photosynthesis of these algae began to change the composition of the atmosphere after entering the atmosphere [1 1]. The appearance and concentration increase of free oxygen in the atmosphere is of great significance to biology. The metabolic pattern of organisms began to change fundamentally, from anaerobic life to aerobic life. The change of metabolic mode has played a role in the evolution and development of organisms. Unicellular eukaryotes appeared about10 ~1500 million years ago, and then gradually formed multicellular organisms, and sexual reproduction began to appear. It can be seen that the evolution of organisms has a strong reaction to the environment, causing environmental changes. The changing environmental conditions have guiding significance for the direction of biological evolution. Human beings have a strong ability to transform and use nature. Man has a greater influence on the natural environment than any other living thing.
Origin and extinction are also the results of organisms not adapting to the environment and being eliminated by the environment.
In fact, it is the same thing as evolution, but the result is different.
I hope it helps you.