Microevolution: The Causes Of Evolutionary Change
If evolution is descent with modification applied to life on Earth, then microevolution can be called the small, measurable evolutionary changes within a population while macroevolution is large evolutionary change over long periods of time - short term and long term/big picture evolution, essentially. Microevolution works on a single population’s genetics and could be said to be the status quo of evolution that occurs consistently and universally while macroevolution occurs over many years or as a result of a drastic change in the population or environment (because a changed environment forces organisms to change to adapt to it or die off). Causes of evolution may include genetic mutation, gene migration, nonrandom mating, and genetic drift,
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which cause microevolution; the similarity between these mechanisms is that they cause diversity and prevent genetic equilibrium. These mechanisms keep the allele and gene frequencies constantly changing - this means, that since phenotypes, as a result of constantly changing genes, are always diverse, allowing natural selection to occur. Causes of macroevolution are the mechanisms of speciation, the formation of new species while evolution occurs, meaning that many species as a whole both affect and are affected by macroevolution, an drastic environmental changes (not discussed). For speciation to occur, there must be a mechanism that isolates parts of a population from each other; in their isolation, new species develop.
A simple explanation of its mechanisms is a good way to understand how microevolution works; mutations, miration, nonrandom mating, and genetic drift (as well as natural selection, which typically follows after all of the other mechanisms) lead to genetic diversity in a population, which allows natural selection to act on the variation.
When natural selection acts on the population, allowing only the fittest members to live, and as the population continues to die and reproduce over time, the population’s overall gene pool has changed from what it originally was, which is the first step in evolution. Mutations are chance alterations in an organism’s DNA that causes their genetic makeup to change. Mutations can affect a population as a whole but also affects the individual, whose mutated genotype may affect its phenotype, causing it to become different from it’s grorup. Natural selection will either allow this individual to live and reproduce (if the mutation is beneficial) or cause it to die due to its genetically induced lack of fitness. Migration occurs when genes are transfered (typically by the travel of organisms) from one population to another, adding diversity as well as adding members to the population it migrates to, causing natural selection to work on this changed group to keep the population number under control and suited to the environment. Nonrandom mating affects a population when organisms sexually reproduce by selecting a mate to reproduce with for a certain reason or a desirable trait. This can be a human controlled mechanism; for example, breeders mate dogs who both have a desirable trait to try and produce an offspring with both desirable traits. This mechanism is wide spread, however, and both humans and other animals tend to select their mates for certain traits, such as female birds tend to select mates who have attractive plummage and ‘singing’ - a subcategory of nonrandom mating called sexual selection. Nonrandom mating results in a
population or individual having a certain phenotype that was decided by the individuals or human, and is still acted on by natural selection because certain traits in offspring tend to become more prevalent, cardiac problems in inbred boxer dogs (due to their lack of diversity in gene pool), which, compared to non inbred dogs, puts them at a lower fitness ; they would be more likely to fall victim to natural selection and die out. Genetic drift is a chance mechanism which invovles members of a population disappearing by chance, and their genetic contribution to the group disappears with them, leaving a gene pool lacking alleles it previously had. Looking at a population of green and black beetles, in which some are green and others are black, if a human stepped on some black beetles, leaving only half the number of black beetles, this means the amount of alleles for black coloring has notably dropped and the percentage of beetles with the green allele has increased, and the individuals in the population couldn’t change this outcome.
Macroevolution, caused by speciation, is more difficult to identify in terms of ‘mechanisms’, but can be explained by looking at speciation over the course of history. Looking at the geological tijme scale, a timeline of earth’s history divided by evolutionary events and qualities of the time period, Earth’s history can be broken into eons, eras, periods, and so on, often characterized by what forms of life had evolved by that time. For example, in the Archean eon, the first life on earth was found (according to the fossil record) to be unicellular organisms, hence why the eon was named ‘Archean’ after archaea, which the first organisms have been suspected to be. An era is smaller than an eon, and, typically, there are many eras within an eon, like the Mezozoic Era within the Phanerozoic Eon, which was an era containing dinosaurs. A period, much smaller than an eon or era, fits within an era, like the Quaternary Period within the Cenozoic Era, in which humans originally evolved. Time does affect macroevolution, but not without speciation. The rate and causes of speciation are what causes macroevolution. Geographic isolation in allotropic speciation can physically separate parts of a species, sometimes due to migration, leading to speciation over time when the now separated groups begin to microevolve within the parameters natural selection allows, until the groups are so different due to the differing environments they have adapted to that they are different species that no longer interbreed. However, new species can develop from an ancestral species within one population, as well, often due to mutations or nonrandom mating, which is called sympatric speciation. More specifically, certain isolating mechanisms allow for members within a population to speciate due to not being able to reproduce together or at all. For example, if individuals within a population live in different habitats, reproduce at different times in a year, or have different behaviors of attracting mates, which are all prezygotic isolating mechanisms and can prevent newly evolved species from merging again. Other times, if two different species try to reproduce to form a new species, the hybrid zygote may die in utero (surely there’s a technical term for this) or the hybrid offspring lives, but is sterile and can not make a new species, again preventing newly evolved species from becoming one again. Dramatic environmental changes can also lead to macroevolution, causing mass extinctions that take away many genes and species and general from the world’s gene pool, making room for new species to evolve and flourish, but this trancends micro or macro influences.
As demomonstrated above, microevolution and macroevolution are often connected, the mechanisms of microevolution causing evolution on a small scale that contributes to macroevolution on a large scale. So technically, one could say the mechanisms of microevolution are the mechanisms of macroevoltion, and that these mechanisms cause microevolution in a species and macroevolution in various species. Furtherore, the mechanisms of microevolution often determine the effectiveness of mechanisms of speciation, or in what ways they are able to affect populations and species.microevolution and macroevolution have both occurred as a result of huge environmental changes and human activity as well. Despite their long explanations of differences, microevolution and macroevolution are truly alike because of how connected they are.
which cause microevolution; the similarity between these mechanisms is that they cause diversity and prevent genetic equilibrium. These mechanisms keep the allele and gene frequencies constantly changing - this means, that since phenotypes, as a result of constantly changing genes, are always diverse, allowing natural selection to occur. Causes of macroevolution are the mechanisms of speciation, the formation of new species while evolution occurs, meaning that many species as a whole both affect and are affected by macroevolution, an drastic environmental changes (not discussed). For speciation to occur, there must be a mechanism that isolates parts of a population from each other; in their isolation, new species develop.
A simple explanation of its mechanisms is a good way to understand how microevolution works; mutations, miration, nonrandom mating, and genetic drift (as well as natural selection, which typically follows after all of the other mechanisms) lead to genetic diversity in a population, which allows natural selection to act on the variation.
When natural selection acts on the population, allowing only the fittest members to live, and as the population continues to die and reproduce over time, the population’s overall gene pool has changed from what it originally was, which is the first step in evolution. Mutations are chance alterations in an organism’s DNA that causes their genetic makeup to change. Mutations can affect a population as a whole but also affects the individual, whose mutated genotype may affect its phenotype, causing it to become different from it’s grorup. Natural selection will either allow this individual to live and reproduce (if the mutation is beneficial) or cause it to die due to its genetically induced lack of fitness. Migration occurs when genes are transfered (typically by the travel of organisms) from one population to another, adding diversity as well as adding members to the population it migrates to, causing natural selection to work on this changed group to keep the population number under control and suited to the environment. Nonrandom mating affects a population when organisms sexually reproduce by selecting a mate to reproduce with for a certain reason or a desirable trait. This can be a human controlled mechanism; for example, breeders mate dogs who both have a desirable trait to try and produce an offspring with both desirable traits. This mechanism is wide spread, however, and both humans and other animals tend to select their mates for certain traits, such as female birds tend to select mates who have attractive plummage and ‘singing’ - a subcategory of nonrandom mating called sexual selection. Nonrandom mating results in a
population or individual having a certain phenotype that was decided by the individuals or human, and is still acted on by natural selection because certain traits in offspring tend to become more prevalent, cardiac problems in inbred boxer dogs (due to their lack of diversity in gene pool), which, compared to non inbred dogs, puts them at a lower fitness ; they would be more likely to fall victim to natural selection and die out. Genetic drift is a chance mechanism which invovles members of a population disappearing by chance, and their genetic contribution to the group disappears with them, leaving a gene pool lacking alleles it previously had. Looking at a population of green and black beetles, in which some are green and others are black, if a human stepped on some black beetles, leaving only half the number of black beetles, this means the amount of alleles for black coloring has notably dropped and the percentage of beetles with the green allele has increased, and the individuals in the population couldn’t change this outcome.
Macroevolution, caused by speciation, is more difficult to identify in terms of ‘mechanisms’, but can be explained by looking at speciation over the course of history. Looking at the geological tijme scale, a timeline of earth’s history divided by evolutionary events and qualities of the time period, Earth’s history can be broken into eons, eras, periods, and so on, often characterized by what forms of life had evolved by that time. For example, in the Archean eon, the first life on earth was found (according to the fossil record) to be unicellular organisms, hence why the eon was named ‘Archean’ after archaea, which the first organisms have been suspected to be. An era is smaller than an eon, and, typically, there are many eras within an eon, like the Mezozoic Era within the Phanerozoic Eon, which was an era containing dinosaurs. A period, much smaller than an eon or era, fits within an era, like the Quaternary Period within the Cenozoic Era, in which humans originally evolved. Time does affect macroevolution, but not without speciation. The rate and causes of speciation are what causes macroevolution. Geographic isolation in allotropic speciation can physically separate parts of a species, sometimes due to migration, leading to speciation over time when the now separated groups begin to microevolve within the parameters natural selection allows, until the groups are so different due to the differing environments they have adapted to that they are different species that no longer interbreed. However, new species can develop from an ancestral species within one population, as well, often due to mutations or nonrandom mating, which is called sympatric speciation. More specifically, certain isolating mechanisms allow for members within a population to speciate due to not being able to reproduce together or at all. For example, if individuals within a population live in different habitats, reproduce at different times in a year, or have different behaviors of attracting mates, which are all prezygotic isolating mechanisms and can prevent newly evolved species from merging again. Other times, if two different species try to reproduce to form a new species, the hybrid zygote may die in utero (surely there’s a technical term for this) or the hybrid offspring lives, but is sterile and can not make a new species, again preventing newly evolved species from becoming one again. Dramatic environmental changes can also lead to macroevolution, causing mass extinctions that take away many genes and species and general from the world’s gene pool, making room for new species to evolve and flourish, but this trancends micro or macro influences.
As demomonstrated above, microevolution and macroevolution are often connected, the mechanisms of microevolution causing evolution on a small scale that contributes to macroevolution on a large scale. So technically, one could say the mechanisms of microevolution are the mechanisms of macroevoltion, and that these mechanisms cause microevolution in a species and macroevolution in various species. Furtherore, the mechanisms of microevolution often determine the effectiveness of mechanisms of speciation, or in what ways they are able to affect populations and species.microevolution and macroevolution have both occurred as a result of huge environmental changes and human activity as well. Despite their long explanations of differences, microevolution and macroevolution are truly alike because of how connected they are.