Lamarck, the Founder of Evolution Part 38

This was succeeded by Rev. J. T. Gulick's profound essays "On Diversity of Evolution under One Set of External Conditions"[235] (1872), and on "Divergent Evolution through c.u.mulative Segregation"[236] (1887).

These and later papers are based on his studies on the land sh.e.l.ls of the Hawaiian Islands. The cause of their extreme diversity of local species is, he claims, not due to climatic conditions, food, enemies, or to natural selection, but to the action of what he calls the "law of segregation."

Fifteen years later Mr. Romanes published his theory of physiological selection, which covered much the same ground.

A very strong little book by an ornithologist of wide experience, Charles Dixon,[237] and refreshing to read, since it is packed with facts, is Lamarckian throughout. The chief factor in the formation of local species is, he thinks, isolation; the others are climatic influences (especially the glacial period), use and disuse, and s.e.xual selection as well as chemical agency. Dixon insists on the "vast importance of isolation in the modification of many forms of life, without the a.s.sistance of natural selection." Again he says: "Natural selection, as has often been remarked, can only preserve a beneficial variation--it cannot originate it, it is not a cause of variation; on the other hand, the use or disuse of organs is a direct cause of variation, and can furnish natural selection with abundance of material to work upon" (p. 49). The book, like the papers of Allen, Ridgway, Gulick, and others, shows the value of isolation or segregation in special areas as a factor in the origination of varieties and species, the result being the prevention of interbreeding, which would otherwise swamp the incipient varieties.

Here might be cited Delboeuf's law:[238]

"When a modification is produced in a very small number of individuals, this modification, even were it advantageous, would be destroyed by heredity, as the favored individuals would be obliged to unite with the unmodified individuals. _Il n'en est rien, cependant._ However great may be the number of forms similar to it, and however small may be the number of dissimilar individuals which would give rise to an isolated individual, we can always, while admitting that the different generations are propagated under the same conditions, meet with a number of generations at the end of which the sum total of the modified individuals will surpa.s.s that of the unmodified individuals." Giard adds that this law is capable of mathematical demonstration. "Thus the continuity or even the periodicity of action of a primary factor, such, for example, as a variation of the _milieu_, shows us the necessary and sufficient condition under which a variety or species originates without the aid of any secondary factor."

Semper,[239] an eminent zoologist and morphologist, who also was the first (in 1863) to criticise Darwin's theory of the mode of formation of coral atolls, though not referring to Lamarck, published a strong, catholic, and original book, which is in general essentially Lamarckian, while not undervaluing Darwin's principle of natural selection. "It appears to me," he says, in the preface, "that of all the properties of the animal organism, Variability is that which may first and most easily be traced by exact investigation to its efficient causes."

"By a rearrangement of the materials of his argument, however, we obtain, as I conceive, convincing proof that external conditions can exert not only a very powerful selective force, but a transforming one as well, although it must be the more limited of the two.

"An organ no longer needed for its original purpose may adapt itself to the altered circ.u.mstances, and alter correspondingly if it contains within itself, as I have explained above, the elements of such a change. Then the influence exerted by the changed conditions will be _transforming_, not _selective_.

"This last view may seem somewhat bold to those readers who know that Darwin, in his theory of selection, has almost entirely set aside the direct transforming influence of external circ.u.mstances.

Yet he seems latterly to be disposed to admit that he had undervalued the transforming as well as the selective influence of external conditions; and it seems to me that his objection to the idea of such an influence rested essentially on the method of his argument, which seemed indispensable for setting his theory of selection and his hypothesis as to the transformation of species in a clear light and on a firm footing" (p. 37).

Dr. H. de Varigny has carried on much farther the kind of experiments begun by Semper. In his _Experimental Evolution_ he employs the Lamarckian factors of environment and use and disuse, regarding the selective factors as secondary.

The Lamarckian factors are also depended upon by the late Professor Eimer in his works on the variation of the wall-lizard and on the markings of birds and mammals (1881-88), his final views being comprised in his general work.[240] The essence of his point of view may be seen by the following quotation:

"According to my conception, the physical and chemical changes which organisms experience during life through the action of the environment, through light or want of light, air, warmth, cold, water, moisture, food, etc., and which they transmit by heredity, are the primary elements in the production of the manifold variety of the organic world, and in the origin of species. From the materials thus supplied the struggle for existence makes its selection. These changes, however, express themselves simply as growth" (p. 22).

In a later paper[241] Eimer proposes the term "orthogenesis," or direct development, in rigorous conformity to law, in a few definite directions. Although this is simply and wholly Lamarckism, Eimer claims that it is not, "for," he strangely enough says, "Lamarck ascribed no efficiency whatever to the effects of outward influences on the animal body, and very little to their effects upon vegetable organisms."

Whereas if he had read his Lamarck carefully, he would have seen that the French evolutionist distinctly states that the environment acts directly on plants and the lower animals, but indirectly on those animals with a brain, meaning the higher vertebrates. The same anti-selection views are held by Eimer's pupil, Piepers,[242] who explains organic evolution by "laws of growth, ... uncontrolled by any process of selection."

Dr. Cunningham likewise, in the preface to his translation of Eimer's work, gives his reasons for adopting Neolamarckian views, concluding that "the theory of selection can never get over the difficulty of the origin of entirely new characters;" that "selection, whether natural or artificial, could not be the essential cause of the evolution of organisms." In an article on "The New Darwinism" (_Westminster Review_, July, 1891) he claims that Weismann's theory of heredity does not explain the origin of horns, venomous teeth, feathers, wings of insects, or mammary glands, phosph.o.r.escent organs, etc., which have arisen on animals whose ancestors never had anything similar.

Discussing the origin of whales and other aquatic mammals, W. Kukenthal suggests that the modifications are partially attributable to mechanical principles. (_Annals and Mag. Nat. Hist._, February, 1891.)

From his studies on the variation of b.u.t.terflies, Karl Jordan[243]

proposes the term "mechanical selection" to account for them, but he points out that this factor can only work on variations produced by other factors. Certain cases, as the similar variation in the same locality of two species of different families, but with the same wing pattern, tell in favor of the direct action of the local surroundings on the markings of the wings.

In the same direction are the essays of Schroeder[244] on the markings of caterpillars, which he ascribes to the colors of the surroundings; of Fischer[245] on the trans.m.u.tations of b.u.t.terflies as the result of changes of temperature, and also Dormeister's[246] earlier paper.

Steinach[247] attributes the color of the lower vertebrates to the direct influence of the light on the pigment cells, as does Biedermann.[248]

In his address on evolution and the factors of evolution, Professor A.

Giard[249] has given due credit to Lamarck as "the creator of transformism," and to the position to be a.s.signed to natural selection as a secondary factor. He quotes at length Lamarck's views published in 1806. After enumerating the primary factors of organic evolution, he places natural selection among his secondary factors, such as heredity, segregation, amixia, etc. On the other hand, he states that Lamarck was not happy in the choice of the examples which he gave to explain the action of habits and use of parts. "Je ne rappellerai par l'histoire tant de fois critique du cou de la giraffe et des cornes de l'escargot."

Another important factor in the evolution of the metazoa or many-celled animals, from the sponges and polyps upward from the one-celled forms or protozoa, is the principle of animal aggregation or colonization advanced by Professor Perrier. As civilization and progressive intelligence in mankind arose from the aggregation of men into tribes or peoples which lived a sedentary life, so the agricultural, building, and other arts forthwith sprang up; and as the social insects owe their higher degree of intelligence to their colonial mode of life, so as soon as unicellular organisms began to become fixed, and form aggregates, the sponge and polyp types of organization resulted, this leading to the gastraea, or ancestral form from which all the higher phyla may have originated.

M. Perrier appears to fully accept Lamarck's views, including his speculations as to wants, and use and disuse. He, however, refuses to accept Lamarck's extreme view as to the origin through effort of entirely new organs. As he says: "Unfortunately, if Lamarck succeeded in explaining in a plausible way the modification of organs already existing, their adaptation to different uses, or even their disappearance from disuse, in regard to the appearance of new organs he made hypotheses so venturesome that they led to the momentary forgetfulness of his other forceful conceptions."[250]

The popular idea of Lamarckism, and which from the first has been prejudicial to his views, is that an animal may acquire an organ by simply wishing for or desiring it, or, as his French critics put it, "Un animal finit toujours par posseder un organe quand il le veut." "Such,"

says Perrier,[251] "is not the idea of Lamarck, who simply attributes the transformations of species to the stimulating action of external conditions, construing it under the expression of wants (_besoins_), and explaining by that word what we now call _adaptations_. Thus the long neck of the giraffe results from the fact that the animal inhabits a country where the foliage is situated at the tops of high trees; the long legs of the wading birds have originated from the fact that these birds are obliged to seek their food in the water without wetting themselves," etc. (See p. 350.)

"Many cases," says Perrier, "may be added to-day to those which Lamarck has cited to support his first law [pp. 303, 346]; the only point which is open to discussion is the extent of the changes which an organ may undergo, through the use it is put to by the animal. It is a simple question of measurement. The possibility of the creation of an organ in consequence of external stimuli is itself a matter which deserves to be studied, and which we have no right to reject without investigation, without observations, or to treat as a ridiculous dream; Lamarck would doubtless have made it more readily accepted, if he had not thought it well to pa.s.s over the intermediate steps by means of wants. It is incontestable that by lack of exercise organs atrophy and disappear."

Finally, says Perrier: "Without doubt the real mechanism of the improvement (_perfectionnement_) of organisms has escaped him [Lamarck], but neither has Darwin explained it. The law of natural selection is not the indication of a process of transformation of animals; it is the expression of the total results. It states these results without showing us how they have been brought about. We indeed see that it tends to the preservation of the most perfect organisms; but Darwin does not show us how the organisms themselves originated. This is a void which we have only during these later years tried to fill" (p. 90).

Dr. J. A. Jeffries, author of an essay "On the Epidermal System of Birds," in a later paper[252] thus frankly expresses his views as to the relations of natural selection to the Lamarckian factors. Referring to Darwin's case of the leg bones of domestic ducks compared with those of wild ducks, and the atrophy of disused organs, he adds:

"In this case, as with most of Lamarck's laws, Darwin has taken them to himself wherever natural selection, s.e.xual selection, and the like have fallen to the ground.

"Darwin's natural selection does not depend, as is popularly supposed, on direct proof, but is adduced as an hypothesis which gains its strength from being compatible with so many facts of correlation between an organism and its surroundings. Yet the same writer who considers natural selection proved will call for positive experimental proof of Lamarck's theory, and refuse to accept its general compatibility with the facts as support. Almost any case where natural selection is held to act by virtue of advantage gained by use of a part is equally compatible with Lamarck's theory of use and development. The wings of birds of great power of flight, the relations of insects to flowers, the claws of beasts of prey, are all cases in point."

Professor J. A. Thomson's useful _Synthetic Summary of the Influence of the Environment upon the Organism_ (1887) takes for its text Spencer's aphorism, that the direct action of the medium was the primordial factor of organic evolution. Professor Geddes relies on the changes in the soil and climate to account for the origin of spines in plants.

The botanist Sachs, in his _Physiology of Plants_ (1887), remarks: "A far greater portion of the phenomena of life are [is] called forth by external influences than one formerly ventured to a.s.sume."

Certain botanists are now strong in the belief that the species of plants have originated through the direct influence of the environment.

Of these the most outspoken is the Rev. Professor G. Henslow. His view is that self-adaptation, by response to the definite action of changed conditions of life, is the true origin of species. In 1894[253] he insisted, "_in the strictest sense of the term_, that natural selection is not wanted as an 'aid' or a 'means' in originating species." In a later paper[254] he rea.s.serts that all variations are definite, that there are no indefinite variations, and that natural selection "can take no part in the origination of varieties." He quotes with approval the conclusion of Mr. Herbert Spencer in 1852, published

"seven years before Darwin and Dr. Wallace superadded natural selection as an aid in the origin of species. He saw no necessity for anything beyond the natural power of change with adaptation; and I venture now to add my own testimony, based upon upwards of a quarter of a century's observations and experiments, which have convinced me that Mr. Spencer was right and Darwin was wrong. His words are as follows: 'The supporters of the development hypothesis can show ... that any existing species, animal or vegetable, when placed under conditions different from its previous ones, immediately begins to undergo certain changes of structure fitting it for the new conditions; ... that in the successive generations these changes continue until ultimately the new conditions become the natural ones.... They can show that throughout all organic nature there is at work a modifying influence of the kind they a.s.sign as the causes of specific differences; an influence which, though slow in its action, does in time, if the circ.u.mstances demand it, produce marked changes.'"[255]

Mr. Henslow adduces observations and experiments by Buckman, Bailey, Lesage, Lothelier, Costantin, Bonnier, and others, all demonstrating that the environment acts directly on the plant.

Henslow also suggests that endogens have originated from exogenous plants through self-adaptation to an aquatic habit,[256] which is in line with our idea that certain cla.s.ses of animals have diverged from the more primitive ones by change of habit, although this has led to the development of new cla.s.s-characteristics by use and disuse, phenomena which naturally do not operate in plants, owing to their fixed conditions.

Other botanists--French, German, and English--have also been led to believe in the direct influence of the _milieu_, or environment. Such are Viet,[257] and Scott Elliot,[258] who attributes the growth of bulbs to the "direct influence of the climate."

In a recent work Costantin[259] shares the belief emphatically held by some German botanists in the direct influence of the environment not only as modifying the form, but also as impressing, without the aid of natural selection, that form on the species or part of its inherited stock; and one chapter is devoted to an attempt to establish the thesis that acquired characters are inherited.

In his essay "On Dynamic Influences in Evolution" W. H. Dall[260] holds the view that--

"The environment stands in a relation to the individual such as the hammer and anvil bear to the blacksmith's hot iron. The organism suffers during its entire existence a continuous series of mechanical impacts, none the less real because invisible, or disguised by the fact that some of them are precipitated by voluntary effort of the individual itself.... It is probable that since the initiation of life upon the planet no two organisms have ever been subjected to exactly the same dynamic influences during their development.... The reactions of the organism against the physical forces and mechanical properties of its environment are abundantly sufficient, if we are granted a single organism, with a tendency to grow, to begin with; time for the operation of the forces; and the principle of the survival of the fittest."

In his paper on the hinge of Pelecypod molluscs and its development, he has pointed out a number of the particular ways in which the dynamics of the environment may act on the characters of the hinge and sh.e.l.l of bivalve molluscs. He has also shown that the initiation and development of the columellar plaits in Voluta, Mitra, and other gasteropod molluscs "are the necessary mechanical result of certain comparatively simple physical conditions; and that the variations and peculiarities connected with these plaits perfectly harmonize with the results which follow within organic material subjected to a.n.a.logous stresses."

In the same line of study is Dr. R. T. Jackson's[261] work on the mechanical origin of characters in the lamellibranch molluscs. "The bivalve nature of the sh.e.l.l doubtless arose," he says, "from the splitting on the median line of a primitive univalvular ancestor;" and he adds: "A parallel case is seen in the development of a bivalve sh.e.l.l in ancient crustaceans;" in both types of sh.e.l.ls "the form is induced by the mechanical conditions of the case." The adductor muscles of bivalve molluscs and crustaceans are, he shows plainly, the necessary consequence of the bivalvular condition.

In his theory as to the origin of the siphon of the clam (_Mya arenaria_), he explains it in a manner identical with Lamarck's explanations of the origin of the wading and swimming birds, etc., even to the use of the words "effort" and "habit."

"In _Mya arenaria_ we find a highly elongated siphon. In the young the siphon hardly extends beyond the borders of the valves, and then the animal lives at or close to the surface. In progressive growth, as the animal burrows deeper, the siphon elongates, until it attains a length many times the total length of the valves.

"The ontogeny of the individual and the paleontology of the family both show that Mya came from a form with a very abbreviated siphon, and it seems evident that the long siphon of this genus was brought about by the effort to reach the surface induced by the habit of deep burial."

"The tendency to equalize the form of growth in a horizontal plane, or the geomalic tendency of Professor Hyatt,[262] is seen markedly in pelecypods. In forms which crawl on the free borders of the valves, the right and left growth in relation to the perpendicular is obvious, and agrees with the right and left sides of the animal.

In Pecten the animal at rest lies on the right valve, and swims or flies with the right valve lowermost. Here equalization to the right and left of the perpendicular line pa.s.sing through the centre of gravity is very marked (especially in the Vola division of the group); but the induced right and left aspect corresponds to the dorsal and ventral sides of the animal, not the right and left sides, as in the former case. Lima, a near ally of Pecten, swims with the edges of the valves perpendicular. In this case the geomalic growth corresponds to the right and left sides of the animal.

"The oyster has a deep or spoon-shaped attached valve, and a flat or flatter free valve. This form, or a modification of it, we find to be characteristic of all pelecypods which are attached to a foreign object of support by the cementation of one valve. All are highly modified, and are strikingly different from the normal form seen in locomotive types of the group. The oyster may be taken as the type of the form adopted by attached pelecypods. The two valves are unequal, the attached valve being concave, the free valve flat; but they are not only unequal, they are often very dissimilar--as different as if they belonged to a distinct type in what would be considered typical forms. This is remarkable as a case of acquired and inherited characteristics finding very different expression in the two valves of a group belonging to a cla.s.s typically equivalvular. The attached valve is the most highly modified, and the free is least modified, retaining more fully ancestral characters. Therefore, it is to the free young before fixation takes place and to the free, least-modified valve that we must turn in tracing genetic relations of attached groups. Another characteristic of attached pelecypods is camerated structure, which is most frequent and extensive in the thick attached valve. The form as above described is characteristic of the Ostreidae, Hinnites, Spondylus, and Plicatula, Dimya, Pernostrea, Aetheria, and Mulleria; and Chama and its near allies. These various genera, though ostreiform in the adult, are equivalvular and of totally different form in the free young. The several types cited are from widely separated families of pelecypods, yet all, under the same given conditions, adopt a closely similar form, which is strong proof that common forces acting on all alike have induced the resulting form.

What the forces are that have induced this form it is not easy to see from the study of this form alone; but the ostrean form is the base of a series, from the summit of which we get a clearer view."

(_Amer. Nat._, pp. 18-20.)

Here we see, plainly brought out by Jackson's researches, that the Lamarckian factors of change of environment and consequently of habit, effort, use and disuse, or mechanical strains resulting in the modifications of some, and even the appearance of new organs, as the adductor muscles, have originated new characters which are peculiar to the cla.s.s, and thus a new cla.s.s has been originated. The mollusca, indeed, show to an unusual extent the influence of a change in environment and of use and disuse in the formation of cla.s.ses.