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. Particularly clear, clear expediency is manifested in the world of living beings. Everything weak, ugly, incapable of reproducing healthy offspring is marked 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.
We will consider this, as well as other forms of protective mechanisms that guard the gene pool of the plant, animal, and human communities.
The transmission of hereditary traits is the main property of living matter.
Reproduction is the most important process by which the very existence of the phenomenon of life on Earth is possible. Regardless of the level of its organization, starting from protozoa and ending with mammals, fertilization (in plants - pollination), which leads 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 interspecific crossbreeding is not excluded. They occur both in vivo and artificially performed by humans, but they always lead to the appearance of either offspring with weakened viability or sterile hybrids. Suffice it to recall the barren mules - the descendants obtained from the crossing of a donkey and a mare. As you can see, there are certain forces that can be considered as some kind of insulating mechanisms. We define them in more detail.
Classification of processes leading to population gene pool stability
In evolutionary doctrine, which is a product of the joint scientific work of natural scientists such as C. Darwin, A.N. Severtsov, G. Spencer, considers the following, widespread phenomena that contribute to the stability of the existence of biological species: these are geographical, reproductive, and ecological isolation. The section of biology, population genetics, is engaged in studying the changes occurring in the gene pool of communities of living organisms. They are the result of factors such as life waves and gene drift.
The aforementioned branch of biology establishes the role of protective factors aimed at preserving the conservativeness of karyotypes of individuals in the population and preventing interpopulation crosses. Next, we will find out what isolating mechanisms are called ecological, and what is their significance in maintaining an unchanged composition of genes in a population.
The role of environmental conditions in preserving the gene pool of communities of living organisms
As a result of phylogenesis - the historical development of the 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 this territory, that is, 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, the divergence of the requirements of both groups regarding the type of food. So, the beetle pea weevil forms two insect communities: one feeds on pea seeds, the other on beans.
In the reproductive period, due to the fact that forage crops grow in different zones, the organisms of the two populations do not interbreed.
Breeding dates and their importance in ensuring the genetic stability of a population
Factors that significantly complicate, or even completely suppress pollination or copulation between organisms of the same systematic category, include insulating mechanisms that control the timing of reproduction of individuals. For example, the flowering of meadow bluegrass, which grows in estuaries, is correlated with the time of the spring flood cessation. Plants living directly on the coast, and during the flood period for a long time under water, bloom later than those individuals who were under the influence of the flood for a short time, or did not flood at all. For obvious reasons, panmixia (cross-pollination) between plants living in different places of the meadow is absent, since pollen ripening occurs at different times. As a result, several populations of meadow bluegrass 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, as well as the frequency of occurrence of both dominant and recessive alleles. This leads to the fact that the gene pools of populations are increasingly different from each other. Such a discrepancy will primarily concern forms of adaptation to abiotic environmental factors. What does it depend on?
The complex effect of various types of insulation
It is based on interconnected environmental 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 is, the divergence of the signs and properties of organisms. It lies at the basis of microevolution - the process leading to the formation of first subspecies, and then new biological species in nature.
How does geographical isolation arise?
Both in botany and in zoology, scientists pay serious attention to the factor, which reduces to almost zero the probability of free cross between individuals of the same species. It received the name of geographical isolation. It turned out that a sharp change in the terrain is necessarily accompanied by the appearance of obstacles leading to the emergence of cardinal differences in organisms.
They relate primarily to the timing of maturation of gametes, the time of copulation or pollination. All these factors can be combined in one term - reproductive isolation. What are the consequences for the existence of a population?
Sign discrepancy
Scientists have found that populations of organisms that have initially similar genomes acquire ever greater divergent features over time due to the disappearance of both a single food supply and the possibility of free crossbreeding. Insurmountable physical barriers in the form of continental faults, uplift of mountain ranges, river spills isolate communities of individuals from each other. It is in this way that wildlife develops. The examples below illustrate geographical isolation as an important speciation mechanism. Thus, the groups of marsupial mammals in Australia, after separating it from the ancient mainland of Gondwana, have significant anatomical and physiological differences from modern European animal species that arose after the Great Glaciation.
C. Darwin on speciation mechanisms
The world-famous creator of the theory of natural selection, the English naturalist Charles Darwin, defined 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 geographical and environmental isolation mechanisms. He drew examples of their manifestation from observations made during his famous round-the-world trip. Darwin saw and sketched 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 various foods.
When crossing among themselves, 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, then turned into independent species. We examined yet another direction of evolution, leading to the formation of new biological species, along which all existing living nature is advancing. The examples discussed above prove the important role of spatial mechanisms that prevent the probability of crosses between organisms of different populations, which ultimately leads to the emergence of new systematic units.