Adaptation (a2430)

ADAPTATION (Adaptation, Anpassung), a term used in biology in two senses: 1) a property of a living organism acquired by it in the course of evolution, useful to it in the environment where it lives, and therefore contributing to the preservation of its life or its offspring, and thus contributing to the preservation of the species, and 2) the very process of acquiring such a property. Adaptation must therefore always be beneficial and must have arisen historically. The equality sign, which Haeckel placed between variation and adaptation, fundamentally does not coincide with Darwin's views. According to the latter, adaptation, a useful change, is the result of the action of selection, while variations can be directed in any direction. The above definition of adaptation forces us not to classify as adaptation that category of purposeful, and therefore beneficial, general properties of the organism that characterize all life and its processes, such as metabolism, reproduction, etc., which make the organism an organism and which must have arisen with the beginning of life. Adaptation will thus include 1) formations acquired in the process of evolution, ready, completed, constant beneficial structures, e.g., wings serving for flight, protective adaptations (see), coloration (see); 2) beneficial reactions for the organism and its offspring, rapid or prolonged, i.e., instincts, e.g., pulling the hand away upon touching something hot, immunity to poisons, wound healing, regeneration, laying of eggs by insects in that environment where their larvae will feed, rapid change of color along with change of environment in a chameleon or octopus, etc. Adaptive formations and reactions are in close connection with the habitat of a particular organism. Rhythmic changes in this environment (change of day and night, seasonal fluctuations) often cause corresponding rhythm in adaptations. E.g., the winter coloration of the stoat, weasel, snow hare, and white ptarmigan is replaced by their summer plumage. Slow (climatic or other) fluctuations in the environment are often accompanied by slow changes in adaptations. With the development of steppes, the ancestors of the horse, which fed on the tender foliage of forests, acquired a new type of teeth, adapted for grinding coarse grains, and developed long limbs with the most developed middle finger for running in open spaces. Theologians, idealists, and vitalists have always considered adaptation as a result of the manifestation of an inherent purposefulness in all organisms. Darwin, however, managed to prove that this adaptability is the result of history, that not all appearing changes are beneficial, adaptive. Modern genetics also asserts that newly appearing hereditary changes under the influence of external conditions, mutations, are not directed (Muller). Adaptability is realized not by the organism itself creating the necessary features for given conditions, but by these features being the result of natural selection, which preserves and thereby strengthens those random traits of variability that in a given situation prove to be adaptive. The existence of non-purposeful traits (usually inherited from life in a different environment) in the form of non-functioning pelvic bones of whales or the clavicle of a cat, etc., the existence of errors in instinct, when the instinct has to work in a rarely encountered combination of conditions, proves the historical nature, relativity of adaptations and contradicts the recognition of their original purposefulness. Also unacceptable is the Lamarckian viewpoint, according to which adaptations, acquired by the organism either under the influence of exercise or under the influence of external conditions, are adequately inherited by it, since the heredity of acquired traits has not been proven. "The breeder," says Darwin, "who wished to reduce the size of his bantam would not think of subjecting it to hunger, but would select the smallest individuals that appeared by chance." One of the most striking examples of adaptation to a new habitat has recently been studied and described by Harms. This is the process going on since the end of the Tertiary period and continuing to the present time of the formation of terrestrial forms from aquatic ones on the northern coasts of Java and Sumatra. The constantly blowing monsoons here bring from the sea an enormous amount of water vapor, detained by high mountains and precipitating in the form of tropical downpours. Rivers therefore wash into the sea a mass of silt, bound on the shores by mangrove trees, the fruits of which bury themselves in the silt and give rise to mangrove bushes growing already in the zone covered by the tidal wave. Thus the shore quickly conquers territory from the sea. Tides and ebbs occur here once a day (so-called "solar") instead of twice (lunar). As a result of this, animals of the extreme tidal zone, with the retreat of water, are forced either to bury themselves in the silt or to adapt to the air environment, all the more so as the land quickly advances on the sea. Every year the shore grows about twenty meters further. Usually adaptation for aquatic animals to land is impossible, because evaporation quickly dries the poorly protected skin, but in Java this danger does not exist, since the humidity of the air at the sea is practically 100%. Harms managed to find a whole series of related forms of fish living in different zones (Periophthalmus) and connected with each other by transitions. Some of them still lead a completely aquatic life, others semi-aquatic and semi-terrestrial, and others are already completely terrestrial forms, so adapted to life on land that they run from the tidal wave, climbing either higher up the shore or onto the trunks and branches of mangrove trees. These fish spawn in water, and their fry live like their ancestors—these gobies (Gobiidae)—in water. The eyes of the fry, initially located on the sides, gradually increase in size and move to the top of the head. The fry themselves stay near the very shore, with the head sticking out of the water. Then they come out to the shore. Their gills disappear and are replaced by cutaneous respiration. The eyes, which are nearsighted, like all fish living in water, become farsighted. This is achieved by changing the way of accommodation of the eye. The muscle that pulled the lens to the retina with the help of a small apparatus, when set at a close distance, began to move the lens away from the retina. The pectoral fins—rudders in the larva—gradually turn into organs for movement on land, acquiring a new joint, thanks to which the part of the fin remote from the body can bend forward and serve as support during rapid movements of Periophthalmus on land and even serve as an organ helping the fish to climb up trunks and branches, embracing branches with these "paws."—Such a series of adaptations to land Harms could also establish in another group of fish in Java—Salariidae, originating from the family Blenniidae (blennies). Harms outlined similar series of adaptations in marine crabs, hermit crabs, and marine Polychaeta (bristle worms). In crabs, gills gradually disappear and the functions of respiration pass to the inner wall of the gill cavity, supplied with a rich network of capillaries. The walls get a folded and cellular structure, resembling the structure of the wall of a frog's lung. The compound eyes of these terrestrial crabs (Ocypodae) reach a special perfection, characteristic only of dragonflies among arthropods. Polychaetes, moving to land, rely on their appendages (parapodia), placing them vertically, which they never do in water, raise their body above the soil and run like large centipedes. Special outgrowths of the parapodia serve for respiration: blood vessels enter here, ring-shaped outgrowths of which are located closely under the skin and ensure gas exchange.—All these animals that have become terrestrial forms show increased energy of movement, with lightning speed hiding in burrows, trees, and crevices of rocks when in danger. Harms explains this process of formation of new terrestrial forms as follows. He considers adaptation to a terrestrial way of life not as changes in genotypes, but 1) as the realization of a complex of existing genes that did not manifest earlier, as it could only manifest in the air environment, and 2) as the suppression of another complex of genes that manifested itself only in the aquatic environment. If we imagine that in fish there is in potency some ability for cutaneous respiration, that some muscles have the ability to contract differently than usual, then we can agree with Harms' interpretation in this. But we must go further. Egger, who systematically processed material on Periophthalmus argentilineatus, showed that this fish, adapted to land and laying its eggs in fresh water, has broken up into a whole series of local (regional) varieties, each of which is confined to at least a small freshwater basin, a small pond, and can hardly interbreed with neighboring forms, as any somewhat large isthmus represents an obstacle for it. This shows that here too we must introduce the factor of selection accompanied by isolation, which is completely ignored by Harms. Undoubtedly, when the shore dries out, only genotypes containing a complex of genes will be preserved, which, when realized, gives forms capable of living outside water; those not having such complexes must die out if their body of water dries up.

In this way, forms with complexes of genes differing to some degree from each other can survive. This is what is meant by local races in almost every puddle. With further drying of the shore, selection will go even further and will more strictly select forms with complexes of genes that are realized for terrestrial life. On the contrary, complexes of genes important for aquatic life will be indifferent to selection and may not be preserved at all, and then terrestrial forms, in case of a reverse change in conditions, will no longer be able to give rise to aquatic forms. Thus, selection and isolation must play the most important role here. However, the possibility is not excluded of the appearance here (perhaps under the influence of new environmental factors, for example, the direct action of tropical sun rays, a higher percentage of oxygen, etc.) of small mutations, i.e., mutations that act only against the background of a certain genotype. Those of them that lead to Adaptation toward terrestrial life can therefore be fixed by selection. Without selection, it is apparently impossible to imagine the process of development of Adaptation. From the point of view of selection, it is easier to imagine the phenomena of the so-called adaptive radiation or Adaptation in the most diverse directions, which every group of organisms rich in individuals gives. Such a group occupies as much space in nature as possible precisely because competition in the struggle for life intensifies between members of such a group that lead the same way of life, have the same food and enemies. Any Adaptation to another way of life, another environment and nutrition weakens the acuteness of this competition. Examples of such adaptive radiation can be found in any number. These are the reptiles of the Mesozoic era, which gave pterodactyls in the air, ichthyosaurs and plesiosaurs in the water, and dinosaurs, carnivorous and herbivorous, on land. These are the marsupials of Australia, which developed a whole fan of forms parallel to the forms of higher mammals in the Old World (the Tasmanian wolf, the Tasmanian ferret, the squirrel, the marsupial mole, the marsupial rodent-wombat similar to the marmot, etc.). These are the forest birds, which according to modern data gave rise several times to inhabitants of open steppes and deserts, of swamps and water, and among water birds one can distinguish birds that obtain food by diving and swimming, and birds that fly and soar over the water. Thus, finally, the higher placental mammals gave rise to groups both in water (perhaps four separate lines of adaptation—pinnipeds, sirenians, toothed and toothless, cetaceans) and one order into the air (bats). Lit.—see literature to the article Darwinism and Variability.