Charles Robert Darwin, the biologist, the psychologists, philosophist, pioneer of evolutionism who put forward the doctrine of biological evolution, which destroys all kinds of idealistic theology and species invariance.
Long before Darwin, many scientists expressed themselves on the a gradual and continuous change in all species of plants and animals, but it was Darwin who put forward a completely new hypothesis regarding living nature, generalizing individual evolutionary ideas into one, the so-called theory of evolution, which was the most widely spread in the world.
Darwin suggested that in competition among animal populations, only those will survive that have properties of benefits under given specific conditions, allowing producing offspring as well. His theory is based on three principles: a) heredity and variability; b) the struggle for existence; c) natural selection.
Variability is an inalienable attribute of all living things. Despite the similarity of living organisms of the same species, two completely identical individuals cannot be found within the population. This variation of features and properties creates the advantage of some organisms over others.
A certain variability, or adaptive modification, is the ability of individuals of one species to react in an identical way to changes in the environment. Such group changes are not inherited, so they can not supply material for evolution..
The core principle of natural selection has the following implications: Organisms have a tendency to overproduce while living space and food are limited, so that creatures must “fight for survival.” Variants exist in individuals within the same population, and individuals with favorable variations that adapt to the environment will survive and multiply offspring, while individuals without favorable variability will be eliminated. His natural selection principle is based on the prevailing “amalgamation genetic” hypothesis at that time

darwin gives a lot of evidence to increase the fitness of organisms to environmental conditions caused by natural selection this for example is widespread among animals of patronizing color making them less noticeable in habitats: night butterflies have a bodycolor corresponding to the surface on which they spend the day; females openly nesting birds capercaillie black grouse hazel grouse have a color of plumage almost indistinguishable from the surrounding background; in the far north many animalsare painted white partridges bears etc. many animals that have special protective devices against eating them by other animals have in addition a warning color for example poisonous or inedible species some animals are endangered in the form of bright repellent spots for example the hamster has a bright color of the abdomen many animals that do not have special protective equipment in terms of body shape and color imitate the protected mimicry many of them have needles spines chitinous cover shell shell scalesand so on. n. in animals a great role as devices playing different kinds of instincts the instinct of caring for offspring the instincts associated with obtaining food and so on. d. among plants a wide variety of adaptations to cross pollination the dispersion of fruits and seeds are widespread all these adaptations could appear only as a result of natural selection ensuring the existence of the species under certain conditions. however darwin noted that the adaptation of organisms to the environment their usefulness along with perfectionis relative in nature this means that when conditions change useful signs may be useless or even harmful. for example in aquatic plants that absorb water and substances dissolved in it by the entire surface of the body the root system is poorly developed but the surface of the shoot and the airy tissue the aerochyma formed by the system of intercellular spaces piercing the entire body plants this increases the contact surface with the environment providing better gas exchange and allows plants to make fuller use of light and absorb carbon dioxide. but when the pond dry up such plants will die very quickly. all their adaptive signs ensuring their prosperity in the water environment are useless outside of it

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