In 1859, the English scientist Charles Darwin published his fundamental work, The Origin of Species by Natural Selection. This book was the first to formulate a modern theory of evolution. Its driving force is natural selection, which, in turn, is divided into several types, including driving selection. Examples of this hypothesis given in the Origin of Species have clearly demonstrated how the mechanism for the development of life on earth works.
The essence of driving selection
The principle of driving selection is that individuals that have received some differences from the general norm adopted by the species are in a preferential position and eventually win the struggle for survival. This is a long and complicated process. Intraspecific variability affects all structures and organs of each species. It concerns both quantitative characteristics (presence or absence of variation), and qualitative (dimensional, counting).
The history of the development of mammals gives researchers numerous examples of a moving form of selection. Their most variable signs are the number of hair per unit area, the mass of various organs, and the number of red blood cells in the blood. During evolution, the size of the human brain increased. A huge number of variations is in the features of attachment of different muscles, the structure of the bronchial tree of the lungs, and the shape of the liver.
Doubtful species
A multitude of intermediate species forms gave rise to motive selection. Examples of this group were given by Darwin himself. This is a British red grouse descended from a Norwegian species, insects of Madeira, birds of the Galapagos Islands. All of them can be described as “doubtful species”. What are their main symptoms? These are forms that are significantly similar to the species, but so similar to some other forms or closely interconnected with the intermediate steps that biologists do not recognize them as independent species.
Such living beings are links in evolution. Doubtful species are actually nascent new ones. They are not so well separated from their ancestors, but they have already begun the process of separation. These are examples of moving selection in animals. They arise as a result of the struggle for life. No matter how insignificant the random changes in appearance are, if they are at least somehow useful, they will no doubt survive and be inherited by the offspring.
Bird Driving Selection
The struggle for existence is primarily a struggle for diet. If the species cannot consolidate its position in the food chain, it will surely die out. Examples of the moving form of natural selection are clearly visible on the appetite of animals.
Consider several species of birds. The great tit eats a mass of insects in one day, equivalent to the mass of its own body, and the long-tailed tit brings its chicks food hundreds of times a day, grabbing 5-6 caterpillars per serving. A pied flycatcher feeds offspring per kilogram of beetles and worms in two weeks. Korolek can eat up to 10 million insects a year. For the same period, the American kestrel must catch up to 300 mice and dozens of small birds. The food delivered by starlings to their chicks can fill three birdhouses.
Each of these cases is an example of the action of a moving form of natural selection. Changes in the stomach, intestines and beak gradually changed the birds. Some of them became sturdier and more fertile, others became large predators, others became extinct, left without food and turned into food for neighbors.
Dominant species
Variety is generated if an animal or plant is widespread throughout the world. Darwin also called these species dominant. It is they who are most often distinguished by driving selection. An example is an ordinary fox living in different regions of Eurasia . It forms several geographical forms, constantly replacing each other. Foxes living in the north are much larger than foxes living in the south, in the zone of steppes and semi-deserts. The smallest of them live in Central Asia, and especially in Afghanistan.
The wide range of the fox world is the result of evolution driven by selection. The example is obvious: animals need to be more durable in the north than in the south. This is due to climatic conditions, and with dangerous neighbors. As the foxes migrated south, each new generation became smaller as a result of small natural changes. New individuals became more adapted to the steppes and deserts and continued to conquer unfamiliar territories.
Driving selection and feed base
All examples of moving natural selection show that in each individual case, nature maintains a biological balance. Even if a new species gains an advantage and becomes dominant, its dominance always has a limit. This principle also manifests itself if a person tries to intervene in natural processes.
In 1911, 25 reindeer were brought to Pribylov Island near Alaska. They took root well in a new place - in 1938 there were already two thousand of them. There were too many individuals, because of which the food supply was undermined and the entire population gradually died out. In 1950, only 8 deer remained on the island. The characteristics of driving selection and examples show that if a species is found to be in too good conditions, it multiplies en masse, destroys the food necessary for itself, and eventually dies itself.
A similar situation has arisen on the Arizona plateau Kaybab, where people, trying to restore the number of black-tailed deer, shot and killed all the coyotes and cougars and prohibited hunting. Exceeding the permissible population density was the starting point of population extinction.
Random mutations
The mechanism of driving selection acts chaotically. Darwin could not understand how the changes that appear in new generations of living organisms are regulated. Scientists of the XX century came to the conclusion that new traits arise in animals and plants as a result of random mutations. They can imperceptibly appear and imperceptibly disappear, but if such changes are useful to the individual, they are saved and inherited by the offspring.
Europeans who discovered Australia brought an ordinary bee to the continent, which quickly exterminated the native bees, which had a smaller sting. This case is artificial. His cause was human activity. But it is precisely on the same principle that natural moving selection acts.
Intraspecific struggle
The struggle for survival is always stubborn, but the struggle for life between individuals and varieties of the same species is doubly stubborn. Affects the similarity in the habits and structure of the body.
In Scotland, in the 19th century, a confrontation was observed between two species of blackbirds - an increase in the number of blackbirds-squirrels led to the disappearance of songbirds. An example of the action of the moving form of natural selection is the fact that in Russia, Asian cockroaches of the Prussians everywhere ousted their larger relatives.
Interspecific struggle
It is important that the structure of any organic creature most significantly affects other creatures living nearby. As a rule, these are competitors who every day fight with each other for survival. So, parasites that live next to tigers have characteristic trailers. They turned out to be more convenient for sticking to the hair of these predatory animals.
Examples of moving selection in plants can also be considered in the context of interspecific struggle. Well-known to everyone, dandelion has crests-flying. They carry seeds and are closely interconnected with the dense population of the territories where this plant is. Such a structure helps not only to survive, but also to reproduce in huge numbers. Seeds on volatiles can spread far through the air and fall on still unoccupied soil.
Expansion
At first glance, the supply of food in the seeds of many plants has nothing to do with other plants. However, in reality they have a fundamental importance. It consists in the growth rate of seedlings, forced to fight with extraneous vegetation surrounding them. In the early stages of existence, young shoots of peas or beans quickly develop. During their own evolution, their seeds began to receive a large supply of food, which helped them occupy a significant niche in the organic world. The competing species of peas and beans, which did not receive this advantage, lost the interspecific struggle and disappeared from the face of the earth.
The above example shows an important pattern. When an animal and plant enters a new country and finds itself among previously unfamiliar competitors, its living conditions change greatly, even if the climate remains the same. In order to gain a foothold in the new territory, the species must necessarily deviate from its ancestors in its development.
Slow selection
Driving selection operates hourly and daily. He preserves and composes useful changes, thereby improving the organic being, depending on the conditions of his life. Selection is slow and invisible to the human eye, but implacable. Evolution cannot be considered for several generations. For this, scientists have to study entire geological eras and periods lasting thousands and millions of years.
Selection can work due to signs that would seem to be completely irrelevant. For example, insects that eat leaves are green, and spotty gray is characteristic of trees that feed on bark. If the color changes, these creatures will become noticeable and vulnerable to predators. Similarly, for a flock of white sheep, the presence of lambs with at least a small black spot is disastrous.
Correlation and adaptation
The signs of living things change not only as a result of random mutations, but also according to the principle of correlation. What is its essence? When one part of the body changes, this will necessarily lead to changes in other parts. Often such evolutionary twists are distinguished by the most unexpected properties.
The main function of change is adaptation. They can occur at various stages of life. For example, in ostrich chicks on the upper part of the beak, characteristic horny tubercles arise, which are also called chick teeth. In the very first days after hatching from an egg, they dissolve and disappear. Their only purpose is to help the chick destroy the shell. This is the so-called embryonic device. They allow the species to increase its birth rate and fight for survival more effectively. Due to such seemingly insignificant features, moving selection functions.