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 over time both the ecosystem and the biosphere as a whole.
Basic theory
There are several versions that explain the mechanisms on which the evolutionary process is built. Most scientists now adhere 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 in 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, by accumulating positive mutations, was able to adapt to new conditions, when returning to the old environment, will have to go through the path of adaptation again. Moreover, no biological species can be fully established, Charles Darwin himself 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 old conditions, but not in the "old" ways.
This can easily be seen in the example of dolphins. The internal structure of their fins (along with cetaceans) retains the signs of mammalian limbs. Mutations update the gene pool of generations, so they never repeat. Despite the fact that dolphins and whales changed their habitat, and five-fingered limbs into fins, they still remain mammals. Just as reptiles evolved from amphibians at a certain stage, but even having returned to their previous environment, they will not be able to give rise to amphibians.
Another example of this rule of evolution: evergreen shrub needle. On its stem are shiny, large and thick leaves, which in fact are mutated branches. True leaves are scaly and located in the center of these "stems". A flower appears from the sinus of the scales in early spring, from which the fetus will later develop. The needle 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 again fell into the aquatic environment, but instead of real foliage, modified stems appeared.
Heterogeneity
The rules of evolution say that the process is very heterogeneous and is not determined by astronomical time. For example, there are animals that have existed unchanged for hundreds of millions of years. These are bristled fish, hatteria and saber tail - 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 been enriched by 240 species of crayfish, which are divided into 34 new genera. The appearance or change of 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 the species reproduces, the higher the rate of evolution.
Closed systems
Processes such as evolution, natural selection, and mutations can go much faster. This happens if the environmental conditions are unstable. However, in deep oceans, cave waters, islands and other isolated territories, evolution, natural selection and speciation are very slow. This explains the fact that cysterae fish have remained unchanged for so many millions of years.
To 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 from pests, but after a few years, species appeared that adapted to the action of the drug. These forms occupied 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 forties, scientists noted the appearance of microorganisms resistant to these drugs.
Patterns
There are three main lines of evolution: convergence, divergence, and parallelism. During divergence, a gradual divergence of intraspecific traits is observed, which eventually leads to new groupings of individuals. As differences in the structure and method of food production become more pronounced, groups begin to diverge across other territories. If one region deals with animals that have the same food needs, then with time, when the supply of food becomes less, they will have to leave the site and adapt to other conditions. If on the same territory there are species with different needs, competition between them is much less.
A striking example of how the evolutionary process of divergence occurs is the 7 species of deer related to each other: these are reindeer, red 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 characters is strengthened, the population is divided into subspecies, which, due to natural selection, can eventually turn into separate species.
Community
Convergence is the evolution of living systems, as a result of which common features appear in unrelated species. An example of convergence is the similarity of body shape in dolphins (mammals), sharks (fish) and ichthyosaurs (reptiles). This is the result of existence in the same habitat and the same living conditions. Climbing agama and 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 is derived from the Greek "parallelos", which means "nearby," and this translation explains its meaning well. Parallelism is the process of independent acquisition of similar structural features among closely related genetic groups, occurring 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 fins as adaptations to the aquatic environment, which in walruses, eared seals and real seals formed in parallel. Also, among many winged insects, the transition of the front wings to the elytra occurred. Brindle fish have signs of amphibians, and bestial-toed lizards have signs of mammals. The presence of parallelism indicates not only the unity of origin of species, but also similar living conditions.