Assimilation (biology)

“ But, on the other hand, while even the most advanced selectionists will doubtless allow that the earliest organic colour, or colours, were probably non-significant, they would be quite justified in opposing the hypothesis of assimilation, as above defined, on the ground that there is no reason whatever to suppose that the direct action of any environment upon an organism must necessarily produce in it a colouration identical with that of its environment ”

“ Can we not more easily imagine that animals assimilated in colour with the monotonous and semi-sombre hues of their then environment; but as they multiplied and the struggle for existence caused migration, the same inherent tendency to assimilative colouration prompted assimilative variation in response to the difference in surrounding conditions, and when this variation became adaptive and protective, the process of natural selection accentuated and perpetuated whatever was advantageous to the creature's existence. ”

“ When we come to consider whether the effects of the environment are inherited, we attack a stronghold of sociologists and historians. Herbert Spencer thought one of the strongest pieces of evidence in this category was to be found in the assimilation of foreigners in the United States. "The descendants of the immigrant Irish," he pointed out, "lose their Celtic aspect and become Americanised.... To say that 'spontaneous variation,' increased by natural selection, can have produced this effect, is going too far." ”

“ Each offshoot, detached from the main body, tends to diverge from the stock type. If it reaches a naturally isolated region, where its contact without is practically cut off, it grows from its own loins, emphasizes its group characteristic by close in-breeding, and tends to show a development related to biological divergence under conditions of isolation. Since man is essentially a gregarious animal, the size of every such migrating band will always prevent the evolution of any sharply defined variety, according to the standard of biology. ”

“ Therefore, if an animal is placed in the sun, its [Pg 90] capacity, that is, its need, to assimilate is increased, although assimilation is much more energetic than before. Need to assimilate or hunger is, therefore, dependent upon the supply of food, although, doubtless, also on other conditions, especially those of light and temperature. If this is true, the hunger of a simple organism that assimilates energetically must be more intense than that of one which assimilates slowly, in spite of the consumption of an enormous quantity of food in the case of the former. ”

“ I share this catholicity of assimilation with other animals, all of which, so far as we know, could thrive equally well on the protoplasm of any of their fellows, or of any plant; but here the assimilative powers of the animal world cease.
A solution of smelling-salts in water with an infinitesimal proportion of some other saline matters, contains all the elementary bodies which enter into the composition of protoplasm; but, as I need hardly say, a hogshead 22of that fluid would not keep a hungry man from starving, nor would it save any animal whatever from a like fate. ”

“ The dissimilarity of the inhabitants of different regions may be attributed to modification through variation and natural selection, and probably in a subordinate degree to the definite influence of different physical conditions. The degrees of dissimilarity will depend on the migration of the more dominant forms of life from one region into another having been more or less effectually prevented, at periods more or less remote;— on the nature and number of the former immigrants — and on the action of the inhabitants on each other in leading to the preservation of different modifications ”

“ In most cases this transformation of an immigrant species takes place so quickly under the influence of the altered struggle for life, that even after a few generations a new species arises from it.
Migration has an especial influence in this way on all organisms with separate sexes. For in them the origin of new species by natural selection is always rendered difficult, or delayed, by the fact that the modified descendants occasionally again mix sexually with the unchanged original form, and thus by crossing return to the first form. ”

“ The more an animal or vegetable species increases, the less is its limited natal place sufficient for its sustenance, and the fiercer the struggle for life; the more rapid the over-population of the natal spot, the more it leads to emigration. These migrations are common to all organisms, and are the real cause of the wide distribution of the different species of organisms over the earth’s surface. Just as men leave over-crowded states, so all animals and plants migrate from their over-crowded primæval homes. ”

“ Fortunately, however, the researches of ethnologists to-day are continually bringing new evidence to show that such widespread migration has indeed taken place. Two radically different policies are advocated by the adherents of one or the other of the two opposing factions in biological theory. For accommodation to climatic conditions may take place either by variation and natural selection or by habitual adaptation transmitted by inheritance. ”

“ We know that insects and plants are so transported. Birds and ocean-currents carry seeds from land to land. Insects on a blade of grass or a fallen bough are carried down a river by the current to found colonies of their race far from their place of origin. And such circumstances give rise to races and varieties among species modifiable by the peculiarities of their new localities. The accidental migrations of man may be considered as belonging to the epoch of culture-migration, since they must more usually have occurred with a race advanced in the art of navigation. ”

“ On these same principles, we can understand, as I have endeavoured to show, why oceanic islands should have few inhabitants, but of these a great number should be endemic or peculiar; and why, in relation to the means of migration, one group of beings, even within the same class, should have all its species endemic, and another group should have all its species common to other quarters of the world. ”

“ Darwin and Dr. Hooker reply that when animals or plants migrate into new countries, whether assisted by man or without his aid, the most successful colonisers appertain by no means to those types which are most allied to the old indigenous species. On the contrary it more frequently happens that members of genera, orders, or even classes, distinct and foreign to the invaded country, make their way most rapidly and become dominant at the expense of the endemic species. ”

“ Moreover, when by sudden immigration or by unusually rapid development, many species of a new group have taken possession of a new area, they will have exterminated in a correspondingly rapid manner many of the old inhabitants; and the forms which thus yield their places will commonly be allied, for they will partake of some inferiority in common. ”

“ In all these cases the migration is certainly of recent date, and it is quite possible that, when a longer time has elapsed, some variations will take place in the new home, but in any case these instances prove that an immigrant species can spread over its new area without immediately varying. ”

“ The study of the mixture of human races in this region has also occupied me much, and I have procured numerous photographs of all the types which I have been able to observe. The principal result at which I have arrived is, that the races bear themselves towards each other as do distinct species; that is to say, that the hybrids, which spring from the crossing of men of different races, are always a mixture of the two primitive types, and never the simple reproduction of the characters of one or the other progenitor, as is the case among the races of domestic animals. ”

“ Assimilation, as the word is here used, brings with it a certain borrowed significance which it carried over from physiology, where it is employed to describe the process of nutrition. By a process of nutrition, somewhat similar to the physiological one, we may conceive alien peoples to be incorporated with, and made part of, the community or state. Ordinarily assimilation goes on silently and unconsciously, and only forces itself into popular conscience when there is some interruption or disturbance of the process. ”

“ But from reasons already assigned I can by no means agree with this naturalist, that migration and isolation are necessary elements for the formation of new species. The importance of isolation is likewise great in preventing, after any physical change in the conditions, such as of climate, elevation of the land, &c., the immigration of better adapted organisms; and thus new places in the natural economy of the district will be left open to be filled up by the modification of the old inhabitants. Lastly, isolation will give time for a new variety to be improved at a slow rate ”

“ Whether such variations or individual differences as may arise will be accumulated through natural selection in a greater or less degree, thus causing a greater or less amount of permanent modification, will depend on many complex contingencies — on the variations being of a beneficial nature, on the freedom of intercrossing, on the slowly changing physical conditions of the country, on the immigration of new colonists, and on the nature of the other inhabitants with which the varying species come into competition. ”

“ In earlier times there was a strong tendency, due to old Biblical notions, to imagine all nations as immigrants to the regions where they are now found. But when a zoologist finds a particular species or variety of animal distributed over a limited area, he makes the most natural assumption, that it has arisen through a local differentiation in that region. ”

“ In ordinary cases nature has not allowed her race to {11} be contaminated with a cross of another race, and agriculturists know how difficult they find always to prevent this,—effect would be trueness. This character and sterility when crossed, and generally a greater amount of difference, are two main features, which distinguish domestic races from species. ”

“ If, when most of the species inhabiting one region are different from those of another region, though closely allied to them, it can be shown that migration from the one region to the other has probably occurred at some former period, our general view will be much strengthened; for the explanation is obvious on the principle of descent with modification. ”

“ All racial progress, or eugenics, therefore, depends on the creation of a good environment, and the fitting of the race to that environment. Every improvement in the environment should bring about a corresponding biological adaptation. The two factors in evolution must go side by side, if the race is to progress in what the human mind considers the direction of advancement. In this sense, euthenics and eugenics bear the same relation to human progress as a man's two legs do to his locomotion. ”

“ Assimilation may be regressive, progressive, or reciprocal. Regressive assimilation is where a sound is assimilated to that which follows it, as in ἕννυμι for ϝεσ-νυμι, from the root vas, or ποσσί, for ποδ-σι (ποδ-σϝ-ι) , and γράμμα for γράφ-μα (τ) . Progressive assimilation is the converse of this, as in στέλλω for στελ-yω, μᾶλλον for μαλ-ιον, mellis for melv-is, or the Æolic ἔστελλα for ἔστελ-σα. Regressive assimilation largely preponderates in our Aryan languages, progressive assimilation in the Ural-Altaic ones ”

“ The exact lines of migration cannot be indicated. We cannot say why certain species and not others have migrated; why certain species have been modified and have given rise to new forms, while others have remained unaltered. We cannot hope to explain such facts, until we can say why one species and not another becomes naturalised by man's agency in a foreign land; why one species ranges twice or thrice as far, and is twice or thrice as common, as another species within their own homes. ”

“ Nor do I believe that any great physical change, as of climate, or any unusual degree of isolation, to check immigration, is necessary in order that new and unoccupied places should be left for natural selection to fill up by improving some of the varying inhabitants. For as all the inhabitants of each country are struggling together with nicely balanced forces, extremely slight modifications in the structure or habits of one species would often give it an advantage over others ”

“ The emigrants must either submit and adapt themselves to these new conditions of life or they perish. By adaptation their peculiar specific character becomes the more changed the greater the difference between the new and the old home. The new climate, the new food, but above all, new neighbours in the forms of other animals and plants, influence and tend to modify the inherited character of the immigrant species, and if it is not hardy enough to resist the influences, then sooner or later a new species must arise out of it. ”

“ Finally, the most marked effect of isolation is seen when individual members of a species are transferred to virgin territory which offers unoccupied areas, suitable not to one particular species alone, but to many nearly related species, so that the immigrant colony can adapt itself to all the different possibilities of life, and develop into a whole circle of species. ”

“ It will probably be found that every gradation still exists in various parts of the world, from a complete coincidence to a complete separation of the breeding and the subsistence areas; and when the natural history of a sufficient number of species is thoroughly worked out we may find every link between species which never leave a restricted area in which they breed and live the whole year round, to those other cases in which the two areas are absolutely separated. ”