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 body color 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 perfection is 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