Knight, made under the direction of Professor Osborn.) Laws of Local Adaptive Radiation and Polyphyletic Evolution, illustrated by two Upper Miocene Horses of the Plains Region of North America.
The effect can also be demonstrated experimentally: thus it has been observed that a xerophyte grown in moist air will lose its characteristic adaptive features, and may even assume those of a hygrophyte.
457) namely, by sharp separation of the primary or stem characters from the secondary or adaptive characters in all the known descendants or branches of a theoretical original form.
In endeavouring to trace the causation of adaptation, it is obvious that it must be due quite as much to properties inherent in the plant as to the action of external conditions; the plant must possess adaptive capacity.
Adaptive in character but pursued without necessary knowledge of the relation between the means employed and the ends attained."
The stimulus of water on the breast may be regarded as a sensory presentation which is followed by a definite and adaptive application of behaviour.
II., and gives rise to adaptive hypertrophy.
The distinctions between animals and plants are in fact obviously secondary and adaptive, and point clearly towards the conception of a common origin for the two forms of life, a conception which is made still more probable by the existence of many low forms in which the primary differences between animals and plants fade out.
Able as von Meyer was, his classification of the Reptilia failed because based upon the single adaptive characters of foot structure.
The most fundamental distinction in analysis is that which must be made between homogeny, or true hereditary resemblance, and those multiple forms of adaptive resemblance which are variously known as cases of " analogy," " parallelism," " convergence " and " homoplasy."
Of these two kinds of genetic and adaptive resemblance, homogeny is the warp composed of the vertical, hereditary strands, which connect animals with their ancestors and their successors, while analogy is the woof, composed of the horizontal strands which tie animals together by their superficial resemblances.
The remark may conveniently find its place here that plants which have reached a high degree of adaptive specialization have come to the end of their tether: a too complicated adjustment has deprived them of the elasticity which would enable them to adapt themselves to any further change in their surroundings, and they would pass away with conditions with which they are too inextricably bound up. Vast floras have doubtless thus found their grave in geologic change.
Fuller knowledge has shown that Macgillivray was ill-advised in laying stress on the systematic value of adaptive characters, but his contributions to anatomy were valuable, and later investigators, in particular H.
Do they originate through the natural selection of those variations which are the more adaptive; or do they originate through the inheritance of those acquired modifications which are impressed on the nervous system in the course of individual and intelligent use ?
The evolution of the cysticercoid, cysticercus and other forms of larvae is a varied adaptive phenomenon.
The rapid variation of certain groups of animals or the acceleration of certain organs is also not evidence of the sudden appearance of new adaptive characters.
Great waves of extinction have followed the long periods of the slow evolution of relatively inadaptive types of tooth and foot structure, as first demonstrated by Waldemar Kowalevsky; thus mammals are repeatedly observed in a cul-de-sac of structure from which there is no escape in an adaptive direction.
If a brief definition of instinct, from the purely biological point of view be required, that given in the Dictionary of Philosophy and Psychology may be accepted: "An inherited reaction of the sensori-motor type, relatively complex 3'p 3' p and markedly adaptive in character, and common to a group of individuals."
In accordance with this we can regard the development as an adaptive one and the scolex as invaginated for protective FIG.
Because of the repetition of analogous physiographic and climatic conditions in regions widely separated both in time and in space, we discover that continental and local adaptive radiations result in the creation of analogous groups of radii among all the vertebrates and invertebrates.
The net result of observation is not favourable to the essentially Darwinian view that the adaptive arises out of the fortuitous by selection, but is rather favourable to the hypothesis of the existence of some quite unknown intrinsic law of life which we are at present totally unable to comprehend or even conceive.
By it he became the first to raise a barbarian tongue to the dignity of a literary language; and the skill, knowledge and adaptive ability it displays make it the crowning testimony of his powers as well as.
With regard to adaptations, it is becoming more and more apparent, as experimental knowledge advances, that it is a fundamental property of every living organism in every stage of its existence to display adaptive response to its environment.
The ingenuity of nature, however, in adapting animals is not infinite, because the same devices are repeatedly employed by her to accomplish the same adaptive ends whether in fishes, reptiles, birds or mammals; thus she has repeated herself at least twenty-four times in the evolution of long-snouted rapacious swimming types of animals.
The consequences of this principle when applied to the adaptations of animals bring us to the very antithesis of Cuvier's supposed "law of correlation," for we find that, while the end results of adaptation are such that all parts of an animal conspire to make the whole adaptive, there is no fixed correlation either in the form or rate of development of parts, and that it is therefore impossible for the palaeontologist to predict the anatomy of an unknown animal from one of its parts only, unless the animal happens to belong to a type generally familiar.
- Diagram demonstrating that there are an indefinite number of combinations of various adaptive types of limbs and feet with various adaptive types of teeth, and that there is no fixed law of correlation between the two series of adaptations.
Starting with the stem forms the descendants of which have passed through either persistent or changed habitats, we reach the underlying idea of the branching law of Lamarck or the law of divergence of Darwin, and find it perhaps most clearly expressed in the words "adaptive radiation" (Osborn), which convey the idea of radii in many directions.
There results from continental and local adaptive radiations the presence in the same geographical region of numerous distinct lines in a given group of animals.
Dr Einar Lonnberg has also recorded certain adaptive peculiarities in the stomach.
Adaptive characters are often hereditary, for instance, the seed of a parasite will produce a parasite, and the same is true of a carnivorous plant.
Their distinctive and adaptive characteristics doubtless began to be established as soon as the phanerogamic flora was constituted.
The former classification into Holochlamyda, Pneumochlamyda and Siphonochlamyda has been abandoned, as it was founded on adaptive characters not always indicative of true affinities.
Treviranus, in the beginning of the 10th century, laid stress on the indefiniteness of variation, but assumed that some of it was adaptive response to the environment, and some due to sexual crossing.
To what extent such responses are transmitted to offspring, and what part they play in the formation of the adaptive characters that are conspicuous in many animals, remain dubious, but it is at least clear that natural selection can favour those individuals and those races which show the greatest power of responsive plasticity in the individual.
There remains open a wide field for inquiry as to the precise relations between selection and variation on the one hand, and their products, specific differences and adaptive structures, but the advance of knowledge has supplied no alternative to the Darwinian principles.
With this comes the whole vast and ever-widening range of inventive and adaptive art, where the uniform hereditary instinct of the cell-forming bee and the nest-building bird is supplanted by multiform processes and constructions, often at first rude and clumsy in comparison to those of the lower instinct, but carried on by the faculty of improvement and new invention into ever higher stages.
To other monocotyledonous families the resemblances are merely of adaptive or vegetative characters.
Exceptions to this rule, as exemplified by the cats, are due to special adaptive causes.
From this point of view the various adaptive modifications of mammalian dentition may be roughly grouped under the headings of piscivorous, carnivorous, insectivorous, omnivorous and herbivorous.
Some of the more striking adaptive modifications in the gametophyte and sporophyte, and certain effects of altered external conditions which have been ascertained experimentally, may be briefly mentioned.
While convincing us that the plants of past ages in the earths history were exposed to very similar conditions of life, and made very much the same adaptive responses as their modern representatives, one of the main results of this line of work has been to reveal important data enabling us to fill various gaps in our morphological knowledge and to obtain a more complete picture of the evolution of tissues in the vascular plants.