No one will deny that the reality around us is harmonious and perfect. It doesn’t matter what or who a person believes in, but around him he sees not only beauty and diversity, but also a harmonious order in which there is no place for chaos. Especially clearly clear expediency is manifested in the world of living beings. Everything weak, ugly, incapable of reproducing he althy offspring is swept away by the action of evolutionary factors, primarily natural selection. Not the last role in it is played by such a biological process as reproductive isolation.
This, as well as other forms of defense mechanisms that guard the gene pool of plant, animal and human communities, we will consider in this paper.
Transmission of hereditary characteristics is the main property of living matter
Reproduction is the most important process, thanks to which the very existence of the phenomenon of life is possibleon the ground. Regardless of the level of its organization, from protozoa to mammals, fertilization (in plants - pollination), leading to the appearance of viable, fertile offspring, occurs only between individuals belonging to a population of the same biological species. Obviously, there are natural isolating mechanisms that control copulation or pollination.
Of course, the possibility of cases of interspecific crossing is not excluded. They occur both in natural conditions and are carried out artificially - by man, but always lead to the appearance of either offspring with weakened viability or sterile hybrids. Suffice it to recall the sterile mules - the descendants obtained from the crossing of a donkey and a mare. As you can see, certain forces are at work here, which can be considered as certain types of isolating mechanisms. Let's define them in more detail.
Classification of processes leading to the stability of the gene pool of populations
In the evolutionary doctrine, which is the product of the joint scientific work of such natural scientists as Ch. Darwin, A. N. Severtsov, G. Spencer, considers the following widespread phenomena that contribute to the stability of the existence of biological species: this is geographical, reproductive and ecological isolation. The section of biology - population genetics, is engaged in the study of changes occurring in the gene pool of communities of living organisms. They are the result of factors such as life waves and genetic drift.
The above branch of biology establishes the role of protective factors aimed at preserving the conservatism of karyotypes of individuals in a population and preventing interpopulation crossings. Next, we will find out what isolating mechanisms are called ecological, and what is their significance in maintaining the unchanged composition of genes in a population.
The role of environmental conditions in the preservation of the gene pool of communities of living organisms
As a result of phylogenesis - the historical development of a species, its individuals form populations that live within the boundaries of a certain territory, called the range. Plant and animal organisms interact with environmental factors, as well as with communities of other species that live in a given territory, that is, they occupy a certain ecological niche. To reduce the severity of competition between populations of the same species, there are certain isolating mechanisms that ensure, for example, that the requirements of both groups regarding the type of food differ. Thus, the pea beetle forms two communities of insects: one feeds on pea seeds, the other on beans.
During the reproductive period, due to the fact that fodder crops grow in different zones, the organisms of the two populations do not interbreed.
The timing of reproduction and their importance in ensuring the genetic stability of the population
To factors that significantly impede, or even completely prevent pollination or copulation between organisms of the same systematiccategory, we can include isolating mechanisms that control the timing of reproduction of individuals. For example, the flowering of bluegrass meadow, growing in the mouths of rivers, is correlated with the time of the end of the spring flood. Plants living directly on the shore, and during the period of flooding for a long time under water, bloom later than those individuals that were under the influence of the flood for a short time, or were not flooded at all. For obvious reasons, there is no panmixia (cross-pollination) between plants living in different parts of the meadow, since their pollen ripens at different times. As a result, several populations of meadow grass meadow are formed, differing in terms of reproduction.
The evolutionary role of isolation
Population genetics has established the fact that the impossibility of the process of exchanging genes between organisms of different races or communities leads to the fact that completely different types of mutations occur in the genotypes of individuals, and the frequency of occurrence of both dominant and recessive alleles also changes. This leads to the fact that the gene pools of populations are increasingly different from each other. This discrepancy will concern, first of all, forms of adaptation to abiotic environmental factors. What does it depend on?
Complex action of various types of insulation
It is based on interconnected ecological and reproductive isolation mechanisms. Biology, in particular, its section - the theory of evolution, reveals their influence on the manifestation of such a global process as divergence, that isdivergence of signs and properties of organisms. It underlies microevolution, a process that leads to the formation of first subspecies, and then new biological species in nature.
How geographic isolation occurs
Both in botany and in zoology, scientists pay serious attention to the factor that reduces the probability of free interbreeding between individuals of the same species to almost zero. It is called geographic isolation. It turned out that a sharp change in the terrain is necessarily accompanied by the appearance of obstacles leading to cardinal differences in organisms.
They concern, first of all, the timing of maturation of gametes, the time of copulation or pollination. All of these factors can be combined under one term - reproductive isolation. What are the consequences for the existence of the population it leads to?
Discrepancies
Scientists have found that populations of organisms with initially similar genomes acquire more and more divergent features over time due to the disappearance of both a single food supply and the possibility of free interbreeding. Insurmountable physical barriers in the form of continental breaks, uplift of mountain ranges, and river overflows isolate communities of individuals from each other. This is the way nature develops. The examples below illustrate geographic isolation as an important mechanism for speciation. Thus, groups of marsupial mammals in Australia, after its separation from the ancient mainland of Gondwana, have significantanatomical and physiological differences from modern European animal species that arose after the Great Glaciation.
Ch. Darwin on the mechanisms of speciation
The world famous creator of the theory of natural selection, the English naturalist Charles Darwin, identified the driving forces of evolution, leading to the emergence of new classes, orders and families of living organisms. Also in his writings, the scientist described the geographical and environmental isolating mechanisms. He drew examples of their manifestation from observations made during his famous trip around the world. Darwin saw and drew various types of finches living in the Galapagos Islands. The birds had cardinal differences in the shape of the beak, the size of the body, and ate different foods.
When crossing between individuals completely lost the ability to form fertile offspring. According to the researcher, the large distances between the islands and the differences in their flora and fauna led to the formation of several subspecies, which then turned into independent species. We have considered one more direction of evolution, leading to the formation of new biological species, along which all living nature is moving forward. The examples we have considered above prove the important role of spatial mechanisms that prevent the possibility of crossing between organisms of different populations, which ultimately leads to the emergence of new systematic units.
