Evolution is a change in the characteristic of inherited biological populations. The process of evolution raises biodiversity at every level of biological organization, including species levels, individual organisms, and molecules.
The repetitive formation of new species (speciation), changes in species (anagenesis), and loss of species (extinction) throughout the evolutionary history of life on Earth are demonstrated by a common set of morphological and biochemical properties, including a common DNA sequence. These common traits are more similar among species with more recent common ancestors, and can be used to reconstruct the biological "tree of life" based on evolutionary (phylogenetic) relationships, using both existing species and fossils. The fossil record includes the development of early biogenic graphite, to microbial mat fossils, to fossils of multicellular organisms. The existing patterns of biodiversity have been established both by speciation and by extinction.
In the mid-19th century, Charles Darwin formulated the theory of scientific evolution through natural selection, published in his book On The Origin of Species (1859). Evolution through natural selection is a process first shown by frequent observations, more generations produced than survivors. This is followed by three observable facts about living organisms: 1) the characteristics vary between individuals with respect to morphology, physiology, and behavior (phenotypic variation), 2) different properties provide different levels of survival and reproduction (differential fitness) , and 3) inherited traits from generation to generation (fitness heritability). Thus, in the next generation of generations the population is replaced by better-adapted parent progeny to survive and reproduce in the biophysical environment where natural selection occurs.
This teleonomy is a quality in which the process of natural selection creates and retains properties that seem to be suitable for their functional role. The process by which change takes place, from one generation to another, is called an evolutionary process or mechanism. The four most widely recognized evolutionary processes are natural selection (including sexual selection), genetic drift, mutation and gene migration due to genetic mixing. Natural selection and variety of genetic shift types; mutations and gene migration create variations.
The consequences of selection may include meiotic drivers (transmission of certain unequal alleles), nonrandom marriage, and genetic jumps. At the beginning of the 20th century, the synthesis of modern evolution integrates classical genetics with Darwin's theory of evolution through natural selection through population genetic discipline. The importance of natural selection as the cause of evolution is accepted in other branches of biology. In addition, previously held concepts of evolution, such as orthogenesis, evolutionism, and other beliefs about congenital "progress" in the largest-scale trends in evolution, are becoming obsolete. Scientists continue to study the various aspects of evolutionary biology by forming and testing hypotheses, building mathematical models of biological theory and biological theory, using observational data, and conducting field experiments as well as in the laboratory.
All life on Earth shares a common ancestor known as the last universal ancestor (LUCA), which lived about 3.5-3.8 billion years ago. A report in December 2017 states that Australia's 3.45 billion year old rocks contain microorganisms, the earliest direct evidence of life on Earth. However, this should not be regarded as the first living organism on Earth; a study in 2015 found "remnants of biotic life" from 4.1 billion years ago in ancient rocks in Western Australia. In July 2016, scientists reported identifying a set of 355 genes from LUCA of all living organisms on Earth. More than 99 percent of all species that have ever lived on Earth are thought to be extinct. Current Earth species estimates range from 10 to 14 million, of which approximately 1.9 million are estimated to have been named and 1.6 million are documented in the central database to date. More recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth today with only one-thousandth of a percent being described.
In terms of practical application, an understanding of evolution has become an instrument for development in various scientific and industrial fields, including agriculture, human and animal medicine, and life sciences in general. Discoveries in evolutionary biology have made a significant impact not only in the branches of traditional biology but also in other academic disciplines, including biological anthropology, and evolutionary psychology. Evolutionary accounting, a sub-field of artificial intelligence, involves applying Darwin's principles to problems in computer science.
Video Evolution
History of evolutionary thought
Classic time
The proposal that one type of organism can be derived from another kind returns to some of the first pre-Socratic Greek philosophers, such as Anaximander and Empedocles. Such proposals lasted until the Roman era. Poet and philosopher Lucretius follows the Empedocles in his great work De rerum natura ( On Nature of Things ).
Medieval
In contrast to these materialistic views, Aristotelianism considers all natural things as the actualization of fixed natural possibilities, known as forms. This is part of a medieval teleological understanding of nature in which all things have a role that is meant to be played in the divine cosmic order. This variation of ideas became the standard understanding of the Middle Ages and was integrated into Christian learning, but Aristotle did not demand that the kind of real organism always correspond to one another with the appropriate metaphysical forms and specifically give examples of how new kinds of life could be happen.
Pre-Darwinian
In the 17th century, modern methods of modern science rejected Aristotle's approach. It sought the explanation of natural phenomena in terms of the same physical law for all things seen and which did not necessitate the existence of a fixed nature category or divine cosmic order. However, this new approach is slow to take root in biological science, the last bastion of the concept of a fixed nature type. John Ray applies one of the more previously common terms for a fixed nature species, "species," for plants and animals, but he strictly identifies each species as a species and proposes that each species be determined by its own generation-perpetuated features generation. The biological classification introduced by Carl Linnaeus in 1735 explicitly acknowledges the hierarchical nature of the species relationship, but still views the species as fixed according to the divine plan.
Other naturalists are currently speculating about the evolution of species changes over time in accordance with the laws of nature. In 1751, Pierre Louis Maupertuis wrote about the natural modifications that occurred during reproduction and accumulated over many generations to produce new species. Georges-Louis Leclerc, Comte de Buffon suggests that species may change into different organisms, and Erasmus Darwin proposes that all warm-blooded animals can be derived from one microorganism (or "filament"). The first full evolutionary scheme was the "transmutation" theory of Jean-Baptiste Lamarck in 1809, which envisioned the spontaneous generation continuing to produce a simpler life form that developed greater complexity in parallel lineages with inherent progressive tendencies, and postulated that at this local level the lineage adapted to the environment by inheriting changes caused by its use or not being used in the parent. (The latter process is then called Lamarckism.) These ideas are condemned by an established naturalist because the speculation lacks empirical support. In particular, Georges Cuvier insists that species are unrelated and fixed, their similarities reflect the divine design for functional needs. Meanwhile, Ray's ideas of kind design have been developed by William Paley into the Natural Theology or Exhibit of Divinity and Nature (1802), which proposes complex adaptations as evidence of divine design and which is admired by Charles Darwin.
Darwin Revolution
The critical break from the concept of a class or type of constant typology in biology comes with the theory of evolution through natural selection, formulated by Charles Darwin in terms of population variables. Partly influenced by the An Essay on Population Principles (1798) by Thomas Robert Malthus, Darwin notes that population growth will lead to a "struggle for existence" where profitable variations prevail when others perish. In every generation, many offspring fail to survive until reproductive age because of limited resources. This could explain the diversity of plants and animals from common ancestors through the work of natural law in the same way for all types of organisms. Darwin developed his theory of "natural selection" beginning in 1838 and wrote his "big book" of the problem when Alfred Russel Wallace sent him a nearly identical version of the theory in 1858. Their separate paper was presented together at a meeting of 1858. from the Linnean Society of London. At the end of 1859, Darwin's publication of his "abstract" as the On the Origin of Species explains natural selection in detail and in a way that led to the acceptance of Darwin's increasingly widespread Darwinian concept at the expense of alternative theory. Thomas Henry Huxley applied Darwin's idea to humans, using comparative paleontology and anatomy to provide strong evidence that humans and apes share a common ancestor. Some are disturbed by this because it implies that humans have no special place in the universe.
Pangenesis and heredity
The mechanisms of reproductive heritability and the origin of new traits remain a mystery. Toward this end, Darwin developed a temporary pangenesis theory. In 1865, Gregor Mendel reported that these traits were inherited in predictable ways through various independent and segregated elements (later known as genes). Mendel's inheritance law eventually replaced most of Darwin's pangenesis theory. August Weismann makes an important distinction between germ cells producing gametes (such as sperm and eggs) and somatic cells of the body, suggesting that heredity passes through the germ line alone. Hugo de Vries relates Darwin's pangenesis theory to the germ cell distinction of Weismann and proposes that Darwinian piran is concentrated in the cell nucleus and when it states that they can move into the cytoplasm to alter the cell structure. De Vries is also one of the researchers who made Mendel's famous work, believing that Mendelian properties associated with the transfer of variations are inherited along the germline. To explain how the new variant originated, de Vries developed a mutation theory that caused a temporary rift between those who accepted Darwinian evolution and biometrics allied to de Vries. In the 1930s, pioneers in the field of population genetics, such as Ronald Fisher, Sewall Wright, and J. B. S. Haldane set the foundation for evolution to a strong statistical philosophy. The false contradiction between Darwin's theory, genetic mutations, and Mendel's legacy is thus reconciled.
'modern synthesis'
In the 1920s and 1930s, the so-called modern synthesis linking natural selection and population genetics, based on Mendelian inheritance, became an integrated theory generally applied to the branch of biology. Modern synthesis explains patterns observed across species in the population, through fossil transitions in paleontology, and complex cellular mechanisms in developmental biology. The publication of DNA structure by James Watson and Francis Crick in 1953 shows the physical mechanism for inheritance. Molecular biology enhances our understanding of the relationship between genotype and phenotype. Progress has also been made in phylogenetic systematics, mapping the transition of traits into a comparative framework and can be tested through the publication and use of evolutionary trees. In 1973, evolutionary biologist Theodosius Dobzhansky wrote that "nothing in biology makes sense except in the light of evolution," because it has brought to light the connection of what first appeared to be discontinuous facts in natural history into a body a coherent explanation of knowledge that explains and predicts many observable facts about life on this planet.
Further synthesis
Since then, modern synthesis has been expanded to explain biological phenomena across the scales of the biological hierarchy, ranging from genes to species. One extension, known as evolutionary developmental biology and informally called "evo-devo," emphasizes how change between generations (evolution) acts on patterns of change in individual organisms (development). Since the beginning of the 21st century and in the light of discoveries made in recent decades, some biologists argue for an extended evolution synthesis, which will explain the effects of non-genetic inheritance modes, such as epigenetic, parental, ecological and cultural effects of heritage, and ability evolved.
Maps Evolution
Heredity
Evolution in organisms occurs through changes in inherited traits - the inherited characteristics of an organism. In humans, for example, eye color is an inherited characteristic and an individual may inherit the "brown eye nature" of one of their parents. The inherited property is controlled by genes and the complete set of genes in the genome of the organism (genetic material) is called its genotype.
The complete set of observable properties that make up the structure and behavior of an organism is called its phenotype. These characteristics are derived from the genotype interaction with the environment. As a result, many aspects of the phenotype of the organism are not inherited. For example, tanned skin comes from the interaction between one's genotype and sunlight; thus, the suntan is not inherited to the children of the person. However, some people are more easily cultivated than others, due to differences in genotype variation; striking examples are those with inherited albinism, which are by no means tanned and very sensitive to sunburn.
Inherited traits are passed from one generation to the next through DNA, a molecule that encodes genetic information. DNA is a long biopolymer consisting of four basic types. The sequence of bases along certain DNA molecules determines genetic information, in a manner similar to the spelling sequence of a sentence. Before the cell divides, the DNA is copied, so that each of the two cells produced will inherit the DNA sequence. Part of the DNA molecule that determines a functional unit is called a gene; Different genes have different base sequences. In cells, long strands of DNA form a thick structure called a chromosome. The specific location of the DNA sequence in chromosomes is known as the locus. If the sequence of DNA in a locus varies between individuals, different forms of this sequence are called alleles. DNA sequences can change through mutations, producing new alleles. If mutations occur within a gene, a new allele may affect the properties controlled by the gene, altering the phenotype of the organism. However, while this simple correspondence between alleles and properties works in some cases, most properties are more complex and controlled by loci of quantitative properties (multiple genes interact).
The latest findings have confirmed important examples of inherited changes that can not be explained by changes in the nucleotide sequence in DNA. This phenomenon is classified as an epigenetic inheritance system. DNA methylation marking chromatin, self-defending metabolic loops, genes silenced by RNA interference and a three-dimensional conformation of proteins (such as prions) are areas where epigenetic inheritance systems have been found at organismic levels. Developmental biologists suggest that complex interactions in genetic tissue and intercellular communication can lead to inheritable variations that may underlie several mechanisms in developmental plasticity and canalization. Heritability can also occur on a larger scale. For example, ecological inheritance through a niche construction process is defined by the activity of a regular and recurrent organism in their environment. This produces a legacy of effects that transform and feed back into the next generation of election regimes. The heredes inherit the gene plus the environmental characteristics generated by the ecological action of the ancestors. Examples of other heritabilities in evolution that are not under the direct control of genes include the inheritance of cultural traits and symbiogenesis.
Variations
The phenotype results of individual organisms both from the genotype and the influence of the environment that has lived in them. An important part of phenotypic variation in the population is caused by genotypic variation. The synthesis of modern evolution defines evolution as a change over time in this genetic variation. The frequency of one particular allele will become more or less common than the other forms of the gene. Variations disappear when new alleles reach their fixation points - when either disappear from the population or replace the entire ancestral allele.
Natural selection will only cause evolution if there is enough genetic variation in a population. Prior to Mendel's genetic discovery, one common hypothesis was the mixing of inheritance. But with mixed inheritance, genetic variances will disappear quickly, making evolution through natural selection unreasonable. The Hardy-Weinberg principle provides a solution to how variations are preserved in populations with Mendel's legacy. The frequency of alleles (variations in genes) will remain constant in the absence of selection, mutation, migration and genetic shift.
Variations originate from mutations in the genome, gene overhaul through sexual reproduction and migration between populations (gene flow). Despite the constant introduction of new variations through mutations and gene flow, most of the genomes of a species are identical in all individuals of the species. However, a relatively small genotype difference can lead to dramatic phenotypic differences: for example, chimpanzees and humans differ only about 5% of their genome.
Mutations
Mutation is a change in the sequence of cell genomic DNA. When mutations occur, they can alter the product from the gene, or prevent the gene from functioning, or have no effect. Based on research in the fly Drosophila melanogaster , it has been suggested that if mutations alter the proteins produced by genes, this may be dangerous, with about 70% of these mutations having damaging effects, and the rest either neutral or less useful.
Mutations can involve large chunks of duplicated chromosomes (usually by genetic recombination), which can introduce additional copies of genes into the genome. Extra gene copies are the main source of raw materials needed for new genes to evolve. This is important because most of the new genes evolved within the gene family of an existing gene that has a common ancestor. For example, the human eye uses four genes to create a light-sensing structure: three for color vision and one for night vision; all four are from a single ancestral genes.
New genes can be generated from the genes of the ancestors when duplicate copies mutate and acquire new functions. This process is easier after the gene is duplicated because it increases system redundancy; one gene in a pair can get a new function while another copy continues to perform its original function. Other types of mutations can even produce an entirely new gene from previously unmodified DNA.
The new gene generation can also involve small parts of some duplicated genes, with these fragments rejoining to form new combinations with new functions. When a new gene is assembled from dragging a pre-existing part, the domain acts as a module with a simple independent function, which can be mixed together to produce new combinations with new and complex functions. For example, polyketide synthase is a large enzyme that makes antibiotics; they contain up to a hundred independent domains each catalyzing a single step in the whole process, such as a step on the assembly line.
Sex and recombination
In asexual organisms, genes are inherited together, or related , because genes can not mix with other organism genes during reproduction. In contrast, the offspring of sexual organisms contain a random mix of their parent's chromosomes generated through independent assortment. In a related process called homologous recombination, sexual organisms exchange DNA between two matching chromosomes. Recombination and reassortment do not alter the frequency of alleles, but instead change which alleles are related to each other, producing offspring with new allele combinations. Sex usually increases genetic variation and can increase the rate of evolution.
Doubling cost of gender was first described by John Maynard Smith. The first cost is that in the sexually dimorphic species only one of the two sexes can give birth to the young. (This cost does not apply to hermaphroditic species, like most plants and many invertebrates.) The second cost is that any sexually reproducing individual can only pass 50% of his genes to every descend, with the least being passed down because every new past generation. But sexual reproduction is a more common means of reproduction among eukaryotes and multicellular organisms. The Red Queen's hypothesis has been used to explain the importance of sexual reproduction as a means of enabling continuous evolution and adaptation in response to evolution along with other species in an ever-changing environment.
Gene flow
Gene flow is the exchange of genes between populations and between species. It can therefore be a source of new variations for a population or a species. Gene flow may be caused by the movement of individuals among separate populations of organisms, as may be caused by the movement of rats between inland and coastal populations, or pollen movement between heavy metal tolerant and sensitive heavy grass populations of metals.
Gene transfer between species includes the formation of hybrid organisms and horizontal gene transfer. Horizontal gene transfer is the transfer of genetic material from one organism to another non-hereditary organism; this is most common among bacteria. In the medical world, this contributes to the spread of antibiotic resistance, such as when one bacterium acquires the resistance gene it quickly transfers it to another species. Gene transfer horizontally from bacteria to eukaryotes such as yeast Saccharomyces cerevisiae and adzuki nut lizard Callosobruchus chinensis has occurred. A large-scale transfer example is the eukaryotic bdelloid rotifer, which has received various genes from bacteria, fungi and plants. Viruses can also carry DNA between organisms, enabling the transfer of genes even across biological domains.
Large-scale gene transfer also occurs between ancestral eukaryotic and bacterial cells, during the acquisition of chloroplasts and mitochondria. It is possible that eukaryotes themselves originate from the horizontal gene transfer between bacteria and archaea.
Mechanism
From a Neo-Darwinian perspective, evolution occurs when there is a change in the frequency of alleles in the population of crossbreeding organisms. For example, alleles for black in the moth population are becoming more common. Mechanisms that can cause changes in allele frequencies include natural selection, genetic aberrations, genetic jumps, mutations and gene flow.
Natural selection
Evolution through natural selection is a process whereby attributes that enhance survival and reproduction become more common in next generation generations. This is often called a "self-explanatory" mechanism because it has to follow from three simple facts:
- Variations exist in organism populations with respect to morphology, physiology, and behavior (phenotypic variations).
- Different features provide different levels of survival and reproduction (differential fitness).
- These traits can be passed down from generation to generation (fitness heritability).
More breeds are produced than may survive, and these conditions result in competition between organisms for survival and reproduction. Consequently, organisms with traits that give them an advantage over their competitors are more likely to pass on their traits to the next generation than those with non-profit properties.
The central concept of natural selection is the evolutionary fitness of an organism. Fitness is measured by the organism's ability to survive and reproduce, which determines the size of its genetic contribution to the next generation. However, fitness is not the same as the number of offspring: not fitness is shown by the proportions of the next generation that carries the genes of the organism. For example, if an organism can survive well and reproduce rapidly, but the offspring are too small and weak to survive, these organisms will give a little genetic contribution to future generations and thus will have a low level of fitness.
If alleles improve fitness more than other alleles of that gene, then with each generation of these alleles will become more common in the population. These characteristics are said to be "selected for ." Examples of properties that can improve fitness are increased survival and increased fecundity. Conversely, the lower the fitness caused by a less favorable allele outcome or damaging this allele less frequently - they are "selected against ." Importantly, fitness alleles are not a fixed characteristic; if the environment changes, previously neutral or dangerous properties may become profitable and the previously beneficial properties become dangerous. However, even if the direction of selection is reversed in this way, the features lost in the past may not evolve in identical form (see Dollo's law). However, the re-activation of dormant genes, as long as they have not been eliminated from the genome and suppressed only for hundreds of generations, may lead to the re-emergence of missing traits such as hindleg in dolphins, chicken teeth, wings on stickless wing insects, and extra nipples in humans, etc. Such "setbacks" are known as atavisms.
The natural selection within a population for properties that can vary across a range of values, such as height, can be categorized into three different types. The first is the selection of directions, which is a shift in the average value of properties over time - for example, the organism is slowly getting higher. Second, the annoying option is selection for extreme trait values ​​and often yields two different values ​​being the most common, with selection against the mean value. This will happen when short or high organisms have an advantage, but not those with medium height. Finally, in stabilizing the selection there is a selection of extreme trait values ​​at both ends, leading to a decrease in variance around the mean and less diversity values. This will, for example, cause the organism to eventually have the same height.
A special case of natural selection is sexual selection, which is a selection for every trait that enhances marital success by increasing the attractiveness of the organism to a potential partner. The nature that evolved through sexual selection is particularly prominent among males of several animal species. Although sexually favored, traits such as elaborate horns, mating calls, large body size and bright colors often attract predation, which jeopardize the survival of male individuals. This scarcity of life is offset by higher reproductive success in men who exhibit these sexually elusive and sexually elusive properties.
The most common natural selection makes the nature of the measure against the individual and the individual traits, more or less likely to survive. "Nature" in this sense refers to the ecosystem, a system in which the organism interacts with every other element, physical or biological, in their local environment. Eugene Odum, an ecological founder, defines an ecosystem as: "Every unit that includes all organisms... in certain areas that interact with the physical environment so that the flow of energy leads to clearly defined trophic structures, biotic diversity and material cycles (eg, exchange of materials between living and non-living parts) within the system. "Each population in the ecosystem occupies different niches, or positions, with different relationships to other parts of the system. This relationship involves the life history of the organism, its position in the food chain and its geographic range. This wide understanding of nature allows scientists to describe certain forces that, together, consist of natural selection.
Natural selection can act at different levels of the organization, such as genes, cells, individual organisms, groups of organisms and species. Selection can act on multiple levels simultaneously. An example of selection that occurs below the level of an individual organism is a gene called transposon, which can replicate and spread throughout the genome. Selection at the level above the individual, such as group selection, allows the evolution of cooperation, as discussed below.
Bias mutation
In addition to being the primary source of variation, mutations can also serve as mechanisms of evolution when there is a different probability at the molecular level for different mutations to occur, a process known as mutation bias. If two genotypes, such as one with G nucleotide and the other with nucleotide A at the same position, have the same fitness, but mutations from G to A occur more frequently than mutations from A to G, then genotypes with A will tend to develop. Different insertion vs. removal of mutation bias in different taxa can lead to the evolution of different genomic sizes. Developmental biases or mutations have also been observed in morphological evolution. For example, according to the theory of evolution of the first phenotype, mutations may eventually lead to genetic assimilation of properties previously caused by the environment.
The effect of mutation bias is superimposed on other processes. If the selection will support one of two mutations, but there is no additional advantage to having both, the most frequent mutations are the most likely to remain in the population. Mutations that cause loss of gene function are much more common than mutations that produce a fully functional new gene. Most loss of function mutations is selected against. But when selection is weak, a mutation bias against loss of function can affect evolution. For example, pigments are no longer useful when animals live in dark caves, and tend to disappear. Such loss of function can occur because of mutation bias, and/or because the function has a cost, and once the benefits of the function disappear, natural selection leads to a loss. The loss of sporulation ability in Bacillus subtilis during laboratory evolution appears to have been caused by mutation bias, rather than natural selection on the cost of maintaining sporulation ability. When there is no selection for loss of function, the rate at which disadvantages evolve depends more on the rate of mutation than on the size of the effective population, indicating that it is driven more by mutation bias than by genetic aberrations. In parasitic organisms, mutation biases lead to selection pressures as seen in Ehrlichia. Mutations are biased against antigenic variants in the outer membrane proteins.
Genetic drift
Genetic drift is the change of allele frequencies from one generation to the next which occurs because alleles have sampling errors. Consequently, when a selective force is absent or relatively weak, the allele frequency tends to "float" up or down randomly (in a random journey). This drift stops when an allele finally becomes fixed, either by disappearing from the population, or completely replacing all other alleles. Genetic drift can therefore remove some alleles from the population by chance alone. Even in the absence of selective forces, genetic drift can lead to two separate populations that begin with the same genetic structure to be divided into two different populations with different sets of alleles.
It is usually difficult to measure the relative importance of selection and neutral processes, including drift. The comparative importance of adaptive and non-adaptive forces in encouraging evolutionary change is the current field of research.
Neutral theory of molecular evolution states that most of the evolutionary changes are the result of fixation of neutral mutations by genetic drift. Therefore, in this model, most of the genetic changes in a population are the result of constant mutation pressure and genetic shift. This neutral form of theory is now largely abandoned, as it seems incompatible with the genetic variations seen in nature. However, a newer and better supported version of this model is a nearly neutral theory, in which mutations that would be effectively neutral in small populations are not necessarily neutral in large populations. Another alternative theory proposes that genetic drift is dwarfed by other stochastic forces in evolution, such as a genetic rope jump, also known as a genetic concept.
The time for neutral alleles becomes fixed by genetic drift depending on population size, with fixation occurring faster in smaller populations. The number of individuals in a population is not critical, but as a measure known as an effective population size. The effective population is usually smaller than the total population because it takes into account factors such as the inbreeding rate and the life cycle stage in which the population is the smallest. An effective population size may not be the same for every gene in the same population.
Genetic hitchhiking
Recombination allows alleles on the same strand of DNA to be separated. However, the recombination rate is low (approximately two events per chromosome per generation). As a result, adjacent genes on chromosomes are not always shifted from each other and adjacent genes tend to be inherited together, a phenomenon known as a relationship. This tendency is measured by finding how often two alleles appear together on one chromosome compared to expectations, called the link imbalance. An allele set that is usually inherited in a group is called a haplotype. This can be important when one allele in a particular haplotype is highly favorable: natural selection may encourage selective sweeps that will also cause other alleles in the haplotype to become more common in the population; This effect is called a genetic piggyback or a genetic concept. The genetic draft caused by the fact that some genetically neutral genes associated with others being selected can be captured in part by an appropriate effective population size.
Gene flow
Gene flow involves the exchange of genes between populations and between species. The presence or absence of gene flow essentially changes the course of evolution. Because of the complexity of the organism, two completely isolated populations will eventually develop genetic mismatches through a neutral process, as in the Bateson-Dobzhansky-Muller model, even if both populations are essentially identical in terms of their adaptation to the environment.
If genetic differentiation between populations develops, the gene flow between populations can introduce attributes or alleles that are detrimental to the local population and this may cause the organisms in this population to evolve a mechanism that prevents mating with a genetically distant population, eventually resulting in the emergence of new species.. Thus, the exchange of genetic information between individuals is essentially important for the development of the concept of biological species.
During the development of modern synthesis, Sewall Wright developed his shift equilibrium theory, which considers the gene flow between partially isolated populations as an important aspect of adaptive evolution. However, there has recently been a substantial critique of the importance of shifting equilibrium theory.
Results
Evolution affects every aspect of the shape and behavior of organisms. Most notable are the specific behavior and physical adaptations that are the result of natural selection. This adaptation improves fitness by helping activities such as finding food, avoiding predators or attracting partners. Organisms can also respond to selection by cooperating with each other, usually by helping their relatives or engaging in mutually beneficial symbiosis. In the long run, evolution produces new species through the separation of the ancestral population of organisms into new groups that can not or will not interbreed.
The results of this evolution are distinguished on a time scale as macroevolution vs. microevolution. Macroevolution refers to evolution occurring at or above the species level, in particular speciation and extinction; whereas microevolution refers to smaller evolutionary changes in a species or population, in particular a shift in gene frequency and adaptation. In general, macro evolution is considered a result of a long period of microevolution. Thus, the difference between micro and macro evolution is not fundamental - the only difference is the time involved. However, in macro evolution, the properties of the whole species may be important. For example, a large number of variations among individuals allow a species to adapt quickly to a new habitat, reducing the possibility of extinction, while a wide geographical range increases the probability of speciation, making it more likely that some of the population will become isolated. In this sense, microevolution and macroevolution may involve selection at different levels - with microevolution that works on genes and organisms, versus macroevolution processes such as the selection of species acting on all species and affecting their degree of speciation and extinction.
A common misconception is that evolution has a purpose, a long-term plan, or an innate tendency for "progress", as expressed in beliefs such as orthogenesis and evolutionism; But realistically, evolution has no long-term goals and does not always result in greater complexity. Although complex species have evolved, they appear as a side effect of the overall number of increasing organisms and simpler life forms still more common in the biosphere. For example, the majority of species are microscopic prokaryotes, which make up about half of the world's biomass despite its small size, and are largely biodiversity of the Earth. Simple organisms have become the dominant life forms on Earth throughout its history and continue to be the main form of life to this day, with complex life just looking more diverse as it is more visible. Indeed, the evolution of microorganisms is essential for modern evolutionary research, because their rapid reproduction allows experimental evolutionary studies and observations of evolution and adaptation in real time.
Adaptation
Adaptation is the process by which organisms are more compatible with their habitats. Also, the term adaptation may refer to properties essential for the survival of an organism. For example, adaptation of horse teeth to grass milling. By using the term adaptation for evolutionary processes and adaptive properties for products (body parts or functions), the two terms can be distinguished. Adaptation is produced by natural selection. The following definition is due to Theodosius Dobzhansky:
- Adaptation is an evolutionary process in which organisms become more able to live in their habitat or habitat.
- Adaptedness is an adapted state: the extent to which an organism is able to live and reproduce in a particular set of habitats.
- The adaptive nature is an aspect of the organism's developmental pattern that enables or enhances the likelihood of the organism surviving and reproducing.
Adaptation can lead to the acquisition of new features, or the loss of ancestral features. An example demonstrating both types of changes is the adaptation of bacteria to antibiotic selection, with genetic changes that cause antibiotic resistance by modifying drug targets, or increasing the activity of transporters that pump drugs out of cells. Another striking example is the bacteria Escherichia coli that evolved the ability to use citric acid as a nutrient in long-term laboratory experiments,
Adaptation takes place through the gradual modification of the existing structure. As a result, structures with similar internal organizations may have different functions in related organisms. This is the result of a single ancestral structure that is adapted to function in different ways. The bones in the bat's wings, for example, are very similar to the bones at the feet of mice and the hands of primates, because the descendants of all these structures are from the same ancestor of mammals. However, since all living organisms are linked to some extent, even organs that seem to have little or no structural similarity, such as arthropods, squid and vertebrate eyes, or limbs and arthropod wings and vertebrates, may depend on a set of homologous genes that control assembly and function; this is called profound homology.
During evolution, some structures may lose their original function and become vestigial structures. Such structures may have little or no function in the current species, but have a clear function in ancestral species, or other closely related species. Examples include pseudogenes, malfunctioning eye residues in fish living in blind caves, the wings of non-flying birds, the presence of pelvic bones in whales and snakes, and sexual characteristics of organisms that reproduce through asexual reproduction. Examples of vestigial structures in humans include wisdom teeth, coccyx, appendix vermiform, and other behavioral remnants such as goose bumps and primitive reflexes.
However, many of the features that appear to be simple adaptations are in fact exaptations: the structure was originally adapted for one function, but by chance it became useful for some other function in the process. One example is the African lizard Holtpis guentheri, who developed a very flat head because it hides in the cracks, as can be seen by seeing his close relative. However, in this species, the head has become so flat that it helps to glide from tree to tree - an exaptation. In cells, molecular machinery such as bacterial flagella and protein sorting machines evolved by the recruitment of some pre-existing proteins that have different functions. Another example is the recruitment of enzymes from glycolysis and xenobiotic metabolism to serve as structural proteins called crystals in the lens of the organism's eye.
A field of current investigation in the biology of evolutionary development is the basis for the development of adaptation and exaptation. This study addresses the origins and evolution of embryonic development and how modification of development and development processes produces new features. These studies have shown that evolution can alter development to produce new structures, such as the embryonic bone structure that develops into the jaws of other animals, rather than being part of the middle ear in mammals. It may also be that structures that have been lost in evolution reappear due to changes in developmental genes, such as mutations in chickens that cause embryos to grow teeth similar to crocodiles. It now becomes clear that most of the changes in the form of organisms are due to changes in a small set of genes that are preserved.
Coevolution
Interaction between organisms can result in conflict and cooperation. When interactions occur between species pairs, such as pathogens and hosts, or predators and prey, this species can develop appropriate sets of adaptations. Here, the evolution of one species causes adaptation to the second species. Changes in this second species, in turn, lead to new adaptations in the first species. This selection and response cycle is called coevolution. An example is the production of tetrodotoxin in coarse newt and the evolution of tetrodotoxin resistance in its predator, common garter snake. In this predator-prey pair, the evolutionary arms race has produced high levels of toxin at high toxin resistance levels and coincides with the height of the snake.
Cooperation
Not all interactions developed together between species involve conflict. Many cases of mutually beneficial interactions have evolved. For example, there is extreme cooperation between crops and mycorrhizal fungi that grow in their roots and help plants absorb nutrients from the soil. This is a reciprocal relationship because the plant provides mushrooms with sugars from photosynthesis. Here, the fungus actually grows inside the plant cells, enabling them to exchange nutrients with their host, while sending out signals that suppress the plant's immune system.
Coalitions among organisms of the same species have also evolved. The extreme case is the eusociality found in social insects, such as bees, termites and ants, in which sterile insects feed and keep a small number of organisms in reproducible colonies. On a smaller scale, the somatic cells that make up the animal body restrict their reproduction so that they can retain stable organisms, which then support small numbers of germ cells to produce offspring. Here, somatic cells respond to specific signals instructing them whether to grow, remain as it is, or die. If the cell ignores these signals and breed inappropriately, its uncontrolled growth causes cancer.
Such cooperation in species may have evolved through the process of family selection, in which one organism acts to help raise the offspring of a relative. This activity is chosen because if helps an individual contains an allele that promotes a relief activity, it is likely that its relative will also contain these alleles and thus the alleles will be forwarded. in. Other processes that can enhance cooperation include group selection, where cooperation provides benefits to a group of organisms.
Speciation
Speciation is the process by which species diverge into two or more derived species.
There are many ways to define the concept of "species." The choice of definition depends on the specificity of the species concerned. For example, some species concepts apply more easily toward sexually reproducing organisms while others lend themselves better to asexual organisms. Despite the diversity of species concepts, these concepts can be placed into one of three broad philosophical approaches: crossbreeding, ecology and phylogenetics. The Biological Species Concept (BSC) is a classic example of a crossbreeding approach. Defined by Ernst Mayr in 1942, the BSC declared that "species are either truly or potentially cross-breeding groups with natural populations, which are reproductively isolated from other such groups." Although its use is broad and long-term, BSCs like others are not without controversy, for example because these concepts can not be applied to prokaryotes, and these are called species problems. Some researchers have sought to unify the monistic definition of species, while others adopt a pluralistic approach and suggest that there may be different ways to logically interpret the definition of a species.
Reproductive barriers between two different sexual populations are needed for the population to become new species. Gene flow can slow this process by spreading new genetic variants as well into other populations. Depending on how far the two species have strayed since their last ancestors, it may still be possible for them to produce offspring, such as with horses and donkey mating to produce a donkey. Such hybrids are generally infertile. In this case, closely related species may be regularly intercrossed, but hybrids will be selected and the species will remain distinct. However, decent hybrids are sometimes formed and these new species can have properties between their parent species, or have an entirely new phenotype. The importance of hybridization in producing new animal species is unclear, although cases have been seen in many species of animals, with gray tree frogs being a highly studied example.
Sputation has been observed several times under both controlled laboratory conditions (see laboratory speciation experiments) and in nature. In sexually reproducing organisms, the speciation results of reproductive isolation are followed by genealogical differences. There are four main geographic modes of speciation. The most common in animals is the allopathic speciation, which occurs in populations that are originally isolated geographically, such as by habitat fragmentation or migration. Selection under these conditions can result in very rapid changes in the appearance and behavior of the organism. When selection and shifting act independently in populations isolated from their other species, separation may eventually lead to organisms that can not be interbreeded.
The second mode of speciation is peripatric speciation, which occurs when small populations of organisms become isolated in new environments. This differs from the allopathic speciation that the numerically isolated population is much smaller than the parent population. Here, the founder effect causes rapid speciation after increased inbreeding increases selection in homozygotes, leading to rapid genetic changes.
The third mode is the parapatric speciation. This is similar to mobile speciation in small populations entering new habitats, but is different because there is no physical separation between these two populations. In contrast, the speciation results from the evolution of mechanisms that reduce the flow of genes between the two populations. Generally this happens when there is a drastic change in the environment in the habitat of the parent species. One example is the Anthoxanthum odoratum grass, which can experience parapatric speciation in response to localized metal pollution from the mine. Here, plants evolve that have resistance to high levels of metal in the soil. Selection of cross-breeding with a parent-sensitive parent population results in gradual changes in the flowering time of a metal-resistant plant, which ultimately produces complete reproductive isolation. Selection of hybrids between two populations can lead to reinforcement, which is the evolution of traits that promote marriage within a species, as well as character displacement, which when two species become more distinct in appearance.
Finally, in species sympatric deviation deviates without geographical isolation or habitat alteration. This form is rare because even a small amount of gene flow can eliminate the genetic differences between the parts of the population. Generally, sympatric speciation in animals requires the evolution of genetic differences and non-random marriage, to enable reproductive isolation to evolve.
One type of sympatric speciation involves cross-breeding of two related species to produce new hybrid species. This is not common in animals because hybrid animals are usually sterile. This is because during meiosis homologous chromosomes from each parent come from different species and can not be successfully paired. However, this is more common in plants because plants often multiply the number of their chromosomes, to form polyploids. This allows the chromosomes of each parent species to form suitable pairs during meiosis, since each parent's chromosome is represented by the couple. An example of a speciation event is when the plant species Arabidopsis thaliana and Arabidopsis arenosa conspire to give the new species Arabidopsis suecica . This occurred about 20,000 years ago, and the speciation process has been repeated in the laboratory, allowing the study of the genetic mechanisms involved in this process. Indeed, doubling chromosomes in a species may be a common cause of reproductive isolation, since half the chromosomes that are doubled will not be matched when breeding with unshrunk organisms.
Speciation events are important in punctuated equilibrium theory, which accounts for patterns in the short fossil record of evolutionary "bursts" interspersed with relatively long stasis, in which species remain relatively unchanged. In this theory, rapidly related speciation and evolution, with natural selection and the strongest genetic shift acting on organisms undergoing speciation in new habitats or small populations. Consequently, the stasis period in the fossil record corresponds to the population of parents and organisms that have speciation and rapid evolution found in small populations or geographically confined habitats and are therefore seldom preserved as fossils.
Extinction
Extinction is the loss of all species. Extinction is not an unusual occurrence, because species regularly appear through speciation and disappear through extinction. Almost all species of animals and plants that live on Earth are now extinct, and extinction seems to be the ultimate fate of all species. This extinction has occurred continuously throughout the history of life, despite the extinction rate of spikes in the event of mass extinction occasionally. The extinction of Cretaceous-Paleogene, where non-avian dinosaurs became extinct, is the most famous, but the previous Permian-Triassic extinction event was even more severe, with about 96% of all endangered marine species. The extinction of the Holocene extinction is a continuous mass extinction associated with human expansion throughout the world over the last few thousand years. The extinction rate is currently 100-1000 times greater than the background level and up to 30% of the species are presumably extinct by the middle of the 21st century. Human activities are now the main cause of ongoing extinction events; global warming can further accelerate in the future.
The role of extinction in evolution is not well understood and may depend on the type of extinction considered. The cause of the continuous "low level" extinction event, which forms the majority of extinctions, may result from inter-species competition for limited resources (the principle of competitive exceptions). If one species can compete with another, it can produce species selection, with more surviving species and other species being driven toward extinction. An intermittent mass extinction is also important, but not as a selective force, but drastically reduces diversity in a non-specific way and encourages rapid evolutionary explosions and speciation in survivors.
Evolutionary life history
Origin
The earth is about 4.54 billion years old. The undeniable earliest evidence of life on Earth dates from at least 3.5 billion years ago, during the Eoarchean Era after the geological crust began to solidify after the previous liquid Hadean Eon. Fossilized microbial mats have been found in a sandstone of 3.48 billion years in Western Australia. Another early physical evidence of a biogenic substance is graphite in the 3.7 billion years of metased experiments found in West Greenland and the "remains of biotic life" found in 4.1 billion years of rock in Western Australia. According to one researcher, "If life appears relatively quickly on Earth... then it can happen in the universe."
More than 99 percent of all species, numbering more than five billion species, that once lived on Earth are thought to be extinct. The estimated number of Earth species currently ranges from 10 million to 14 million, of which approximately 1.9 million are predicted to be named and 1.6 million are documented in the central database to date, leaving at least 80 percent unexplained.
Highly energetic chemistry is thought to have produced self-replicating molecules about 4 billion years ago, and half a billion years later the last ancestors of all life existed. The current scientific consensus is that the complex biochemistry that shapes life comes from simpler chemical reactions. Early life may include self-replicating molecules such as RNA and simple cell assembly.
General descent
All organisms on Earth are descendants of a common ancestor or ancestral gene pool. The current species is a stage in the evolutionary process, with their diversity of products from a long series of speciation events and extinctions. The descendant of a common organism is first inferred from four simple facts about organisms: First, they have geographic distributions that can not be accounted for by local adaptations. Second, the diversity of life is not a completely unique set of organisms, but organisms that share morphological similarities. Third, vestigial features aimlessly resemble the characteristics of functional ancestors and finally, organisms that can be classified using this similarity into a hierarchy of stratified groups - similar to a family tree. However, modern research has suggested that, due to the transfer of horizontal genes, this "tree of life" may be more complicated than simple branching trees because some genes have spread independently between different species.
The last species also left a record of their evolutionary history. Fossils, along with the comparative anatomy of present-day organisms, are morphological, or anatomical. By comparing the anatomy of modern and extinct species, paleontologists can infer the lineage of the species. However, this approach works best for organisms that have hard body parts, such as shells, bones or teeth. Furthermore, as prokaryotes such as bacteria and archaea share a limited set of general morphology, their fossils do not provide information about their ancestors.
More recently, evidence for common ancestry comes from studies of biochemical similarities between organisms. For example, all living cells use the same basic set of nucleotides and amino acids. The development of molecular genetics has revealed the remaining evolutionary records in the genomes of organisms: dating when species diverge through the molecular clock generated by mutations. For example, this comparison of DNA sequences has revealed that humans and chimpanzees share 98% of their genomes and analyze some of the areas in which they differ helps to explain when the common ancestors of this species existed.
Evolution of life
Prokaryotes inhabit Earth from about 3-4 billion years ago. There is no obvious change in the morphology or cellular organization that occurs in these organisms over the next few billion years. Eukaryotic cells emerged between 1.6 and 2.7 billion years ago. The next major change in cell structure occurs when bacteria are engulfed by eukaryotic cells, in a cooperative association called endosimbiosis. Bacteria swallowed and host cells subsequently coevolved, with bacteria evolving into mitochondria or hydrogenosomes. Another transplant of cyanobacterial-like organisms causes chloroplast formation in algae and plants.
The history of life is that of the unicellular eukaryotes, prokaryotes and archaea until about 610 million years ago when multicellular organisms began to appear in the oceans in the Ediacaran period. The evolution of multicellularity occurs in independent events, in diverse organisms such as sponges, brown algae, cyanobacteria, slime molds, and myxobacteria. In January 2016, scientists reported that, about 800 million years ago, a small genetic change in a single molecule called GK-PID might have allowed the organism to move from one organ of the organism to one of many cells.
Soon after the emergence of these first multicellular organisms, a large amount of biodiversity emerged about 10 million years, in an event called the Cambrian explosion. Here, most types of modern animals appear in the fossil record, as well as the lineage
Source of the article : Wikipedia
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