Biological evolution implies the natural development of living organisms, which is accompanied by changes in the genetic composition of populations, as well as an increase in adaptive properties, the emergence of new species and the extinction of old ones. All these factors change both the ecosystem and the biosphere as a whole over time.
Basic Theory
There are several versions explaining the mechanisms on which the evolutionary process is built. Most scientists are now committed to the synthetic theory of evolution (STE), based on the fusion of population genetics and Darwinism. Synthetic theory explains the relationship between genetic mutations, that is, the material of evolution, and natural selection (the mechanism of evolution). The evolutionary process within the framework of this theory is the process of changing the frequencies of alleles of various genes in species populations over the course of several generations.
Patterns and rules of evolution
Evolution is an irreversible process. Any organism that, through the accumulation of positive mutations, was able to adapt to new conditions, when returning to its previous environment, will have to go through the path of adaptation again. Moreover, no biological species can be completely established,Charles Darwin wrote that even if the habitat becomes the same as before, the evolved species will not be able to return to its former state. That is, animals will be able to adapt to the return of the old conditions, but not in the "old" ways.
This can be easily seen in the case of dolphins. The internal structure of their fins (along with cetaceans) retains the features of the limbs of mammals. Mutations update the gene pool of a generation, so they never repeat. Despite the fact that dolphins and whales have changed their habitat, and five-fingered limbs have changed to fins, they are still mammals. Just like reptiles evolved from amphibians at a certain stage, but even returning to their previous environment, they will not be able to give rise to amphibians.
Another example of this evolutionary rule: the evergreen shrub Ruscus. On its stem are shiny, large and thick leaves, which are actually modified branches. True leaves are scaly and are located in the center of these "stems". A flower appears from the sinus of the scale in early spring, from which the fruit will develop later. Butcher's needle got rid of the leaves in the process of evolution, as a result of which it was able to adapt to drought, but then it again fell into the aquatic environment, but instead of real foliage, modified stems appeared.
Heterogeneity
The rules of evolution state that the process is very heterogeneous and is not determined by astronomical time. For example, there are animals that have existed inunchanged for hundreds of millions of years. These are lobe-finned fish, tuatara and saber-tail are living fossils. But it happens that speciation and modification occurs very quickly. Over the past 800 thousand years, new species of rodents have arisen in Australia and the Philippines, and Lake Baikal over the past 20 million years has enriched itself with 240 species of crayfish, which are divided into 34 new genera. The emergence or change of a species does not depend on time as such, but is determined by the lack of fitness and the number of generations. That is, the faster a species reproduces, the higher the rate of evolution.
Closed systems
Processes such as evolution, natural selection and mutation can go much faster. This happens when the environmental conditions are unstable. However, in deep oceans, cave waters, islands, and other isolated areas, evolution, natural selection, and speciation are very slow. This explains the fact that lobe-finned fish remain unchanged for so many millions of years.
Trace the dependence of evolution on the rate of natural selection is quite simple on insects. In the thirties of the last century, poisonous drugs began to be used against pests, but after a few years, species appeared that adapted to the action of the drug. These forms have taken a dominant position and quickly spread across the planet.
For the treatment of many diseases, strong antibiotics were often used - penicillin, streptomycin, gramicidin. The rules of evolution came into force: already in the fortiesscientists have noted the emergence of microorganisms resistant to these drugs.
Patterns
There are three main directions of evolution: convergence, divergence and parallelism. During divergence, a gradual divergence of intraspecific characters is observed, which eventually leads to new groupings of individuals. As the differences in structure and method of obtaining food become more pronounced, the groupings begin to disperse to other territories. If one area is occupied by animals with the same food requirements, then over time, when the food supply becomes smaller, they will have to leave the area and adapt to different conditions. If in the same territory there are species with different needs, the competition between them is much less.
A vivid example of how the evolutionary process of divergence occurs is 7 species of deer related to each other: these are reindeer, deer, elk, sika deer, fallow deer, musk deer and roe deer.
Species with a high degree of divergence have the ability to leave large offspring and compete less with each other. When the divergence of traits is strengthened, the population is divided into subspecies, which, due to natural selection, may eventually turn into separate species.
Community
Convergence is also called the evolution of living systems, as a result of which unrelated species have common features. An example of convergence is the similarity of body shape indolphins (mammals), sharks (fish) and ichthyosaurs (reptiles). This is the result of existence in the same habitat and the same living conditions. The climbing agama and the chameleon are also unrelated, but very similar in appearance. Wings are also an example of convergence. In bats and birds, they arose by changing the forelimbs, but in a butterfly, these are growths of the body. Convergence is very common among the species diversity of the planet.
Parallelism
This term comes from the Greek "parallelos" which means "walking beside" and this translation does a good job of explaining its meaning. Parallelism is the process of independent acquisition of similar structural features among closely related genetic groups, which occurs due to the presence of features inherited from common ancestors. This type of evolution is widespread in nature. An example of this is the appearance of flippers as adaptations to the aquatic environment, which in walruses, eared seals and true seals formed in parallel. Also, among many winged insects, there was a transition of the forewings to the elytra. The lobe-finned fishes have signs of amphibians, and the animal-toothed lizards have signs of mammals. The presence of parallelism testifies not only to the unity of the origin of species, but also to similar conditions of existence.
