The microevolution it is defined as the development of variation within a population. During this process, the evolutionary forces that lead to the formation of new species act: natural selection, gene drift, mutations and migrations. To study it, evolutionary biologists rely on genetic changes that occur in populations.
The concept is opposed to macroevolution, which conceptually occurs at high taxonomic levels, call it genus, families, orders, classes, etc. The search for a bridge between both processes has been widely debated among evolutionary biologists..
Currently, there are very specific examples of evolution at the population or species level, such as industrial melanism, resistance to antibiotics and pesticides, among others..
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The term microevolution - and, together, macroevolution - can be traced back to 1930, where Filipchenko used it for the first time. In this context, the term makes it possible to differentiate the evolutionary process within and above the species level..
Probably for sheer convenience, such terminology (and the original meaning associated with it) was retained by Dobzhansky. In contrast, Goldschmidt argues that microevolution is not sufficient to explain macroevolution, creating one of the most important debates in evolutionary biology..
From Mayr's perspective, a microevolutionary process is defined as one that occurs in relatively short periods of time and at a low systematic category, generally at the species level..
According to the current perspective, microevolution is a process confined within the limits of what we define as “species”. More precisely, to populations of organisms.
It also considers the formation and divergence of new species by evolutionary forces acting within and between populations of organisms. These forces are natural selection, mutations, gene drift, and migrations..
Population genetics is the branch of biology in charge of studying microevolutionary changes. According to this discipline, evolution is defined as the change of allelic frequencies over time. Remember that an allele is a variant or form of a gene.
Thus, the two most important characteristics of microevolution involve the small time scale at which it occurs, and the low taxonomic level - generally low species..
One of the most popular misunderstandings of evolution is that it is conceived as a process that acts strictly on huge time scales, imperceptible to our short lifespan..
However, as we will see later in the examples, there are cases where we can see evolution with our own eyes, at minimal time scales..
From this point of view, microevolution is a process that acts on a small time scale. Some biologists argue that macroevolution is simply microevolution spread over millions or thousands of years..
However, there is the opposite view. In this case, the previous postulation is considered reductionist and they propose that the macroevolution mechanism is independent of microevolution.
The postulants of the first vision are called syntheists, while the punctuationists hold the “decoupled” view of both evolutionary phenomena..
The following examples have been widely used in the literature. To understand them, it is necessary to understand how natural selection works.
This process is the logical result of three postulates: the individuals that make up the species are variable, some of these variations are passed on to their descendants - that is, they are heritable, and finally the survival and reproduction of individuals are not random; those with favorable variations are reproduced.
In other words, in a population whose members show variations, individuals whose particular heritable traits increase their ability to reproduce will disproportionately reproduce..
The most famous example of evolution at the population level is, without a doubt, the phenomenon called "industrial melanism" of moths of the genus Biston betularia. It was observed for the first time in England, parallel to the development of the industrial revolution
In the same way that humans can have brown or blonde hair, the moth can come in two forms, a black and a white morph. That is, the same species has alternative colorations.
The Industrial Revolution was characterized by raising pollution levels in Europe to extraordinary levels. In this way, the bark of the trees on which the moth rested began to accumulate soot and took on a darker color..
Before this phenomenon occurred, the predominant form in the moth population was the clearest form. After the revolution and the blackening of the crusts, the dark form began to increase in frequency, becoming the dominant morph.
Why did this change occur? One of the most accepted explanations holds that the black moths managed to hide better from their predators, the birds, in the new dark bark. Similarly, the lighter version of this species was now more visible to potential predators..
One of the biggest problems facing modern medicine is resistance to antibiotics. After its discovery, it was relatively easy to treat diseases of bacterial origin, increasing the life expectancy of the population.
However, its exaggerated and massive use - in many cases unnecessary - has complicated the situation..
Today, there are a significant number of bacteria that are practically resistant to most of the commonly used antibiotics. And this fact is explained by applying the basic principles of evolution by natural selection..
When an antibiotic is used for the first time, it manages to eliminate the vast majority of bacteria from the system. However, among the surviving cells, there will be variants that are resistant to the antibiotic, a consequence of a particular characteristic in the genome..
In this way, organisms that carry the gene for resistance will generate more offspring than susceptible variants. In an antibiotic environment, resistant bacteria will proliferate disproportionately.
The same reasoning that we use for antibiotics, we can extrapolate to the populations of insects considered pests and to the pesticides that are applied to achieve their elimination.
By applying the selective agent - the pesticide - we are favoring the reproduction of resistant individuals, since we largely eliminate their competition, formed by organisms that are susceptible to the pesticide..
Prolonged application of the same chemical product will inevitably make it ineffective..
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