ADAPTATION, the power andprocess of gradual change in an organism to fit it to its environment. See BIOLOGY i EVOLUTION.
Life came to be, it is inferred, when the gradually accumulated energy which resulting in physical and chemical forces forced a bet ter medium for its interchange, which science, to-day, symbolizes under the term vitalism.
This is then a sort of superchemistry which arose out of the need of handling the cosmical energy constantly being delivered to the earth's surface. One of the methods of inter play between the living matter and its environ ment is adaptation. This adaptation is never perfect save in those forms which become fixed and these are on the decline in struc tural differentiation. They cease to evolve to higher types, for evolution implies new con quests over the environment.
By the terms environment, surroundings, conditions of life, medium or milieu, or monde ambient, is meant everything outside of the individual plant or animal, between which and the living matter there is an energy inter change. The nature of the earth's surface, of the soil, of well-watered regions, of deserts, plains or barrens, the physics of the air and sea, are taught in our textbooks of physical geography. Each such area is inhabited by assemblages of living beings adapted well or ill to such or such conditions. We speak of alpine or arctic life, of the flora and fauna of deserts, of mountains, of lowlands, of the great plains, of forests, of the coasts and abysses of the sea. The word °fauna' means the assemblage of animals inhabiting any area, as the word °flora" is used for the plants. Now each of these areas, with its peculiar surface features, climate, soil, etc., is charac terized by a set of plants and animals which flourish better there than in adjoining regions, and hence are spoken of as being better adapted.
The most unique cases of adaptation to extreme conditions of life are seen in animals living in the darkness of caves, or in the dark abysses of the sea, or parasitic animals, as the fluke and tapeworm, the root-barnacles (Sae culina), the fish-louse (Leetura) and many in sects. In all these forms the body has, as the result of a parasitic life, undergone profound modification, becoming so atrophied in certain respects as to present the utmost contrast to their free-living allies. Adaptation is contin ually correlated with certain given conditions. If the conditions be changed, in time the or ganisms, unless they are modified and changed to what are called new species, become un adapted, unfit for the new environment and unsuccessful in the struggle for existence.
Extinct species are such unfit, unadapted forms. However well, adapted they were at the period in which they lived, when the con ditions of existence changed; when the climate changed from warm to cold, or the reverse; when the soil changed its elevation above the sea, or degree of dryness or humidity; when one area subsided; and another became ele certain species or groups of species, unless they migrated, or were plastic enough to undergo modification and become what are called 'znew)) species or ((new* genera, unable to resist the change, died out,— became ex tinct. The harder parts of these extinct spe
cies are found in the rocks and are called They are the relics of former worlds, witnesses of the profound changes in physical geography through which the earth has passed.
Extinction has not yet taken place for cer tain forms. A few ancient primitive forms have persisted and are still flourishing. Such are many of the Protozoa (Saccamina and others), the Lingulella and Lingula, the king crab (Limulus), the Peripatus and Scolopen drella, which are probably the ancestral forms of insects; among the fishes the Australian lung-fish (Ceratodus), and among lizards the Hatteria of New Zealand. These forms, for various reasons, have withstood the most wide spread and the profoundest geological changes, but they are exceptional. • On the other hand a vast number of species which were plastic i enough to yield to the changes in their sur roundings and became modified into new spe cies became adapted to new conditions of ex istence. It is undoubtedly the case, then, that certain forms become maladapted and suffer extinction, though all through the ages the plant and animal census by no means became at any time lessened, but rather gradually in creased in extent. Another fact clearly estab lished is that the earlier forms were generalized and the later were specialized, and the former, the ancestors of the present species, had to make way for their more specialized descend ants. Thus the trilobites were succeeded by the king-crabs, the creeping dinosaurs were succeeded by the flying reptiles or pterodactyls, and the highly generalized tailed Amphibia yielded the right of way to the tailless frogs and toads of the present day. Adaptation, then, is the process of modification of organ isms caused by changes in the conditions of life. The most fascinating of all adaptive forms is man, who retains all of the charac ters which have been found most valuable for the utilization of more and more of the energy of the environment and who through struc tural specialization has fashioned organs of increasing efficiency to utilize these energy re sources. The chief tool of adaptation of man is his use of symbols by i means of his brain structures, which have given him increasing power to manage the vast amounts of energy which have been and are being subject to con stant interchange.