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 class, and thus a new class 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 classes.
Lang’s treatment, in his Text-book of Comparative Anatomy (1888), of the subjects of the musculature of worms and crustacea, and of the mechanism of the motion of the segmented body in the Arthropoda, is of much value in relation to the mechanical genesis of the body segments and limbs of the members of this type. Dr. B. Sharp has also discussed the same subject (American Naturalist, 1893, p. 89), also Graber in his works, while the present writer in his Text-book of Entomology (1898) has attempted to treat of the mechanical origin of the segments of insects, and of the limbs and their jointed structure, along the lines laid down by Herbert Spencer, Lang, Sharp, and Graber.
W. Roux[263] has inquired how natural selection could have determined the special orientation of the sheets of spongy tissue of bone. He contends that the selection of accidental variation could not originate species, because such variations are isolated, and because, to constitute a real advantage, they should rest on several characters taken together. His example is the transformation of aquatic into terrestrial animals.
G. Pfeffer[264] opposes the efficacy of natural selection, as do C. Emery[265] and O. Hertwig. The essence of Hertwig’s The Biological Problem of To-day (1894) is that “in obedience to different external influences the same rudiments may give rise to different adult structures” (p. 128). Delage, in his Théories sur l’Hérédité, summarizes under seven heads the objections of these distinguished biologists. Species arise, he says, from general variations, due to change in the conditions of life, such as food, climate, use and disuse, very rarely individual variations, such as sports or aberrations, which are more or less the result of disease.
Mention should also be made of the essays and works of H. Driesch,[266] De Varigny,[267] Danilewsky,[268] Verworn,[269] Davenport,[270] Gadow,[271] and others.
In his address on “Neodarwinism and Neolamarckism,” Mr. Lester F. Ward, the palæobotanist, says:
“I shall be obliged to confine myself almost exclusively to the one great mind, who far more than all others combined paved the way for the new science of biology to be founded by Darwin, namely, Lamarck.” After showing that Lamarck established the functional, or what we would call the dynamic factors, he goes on to say that “Lamarck, although he clearly grasped the law of competition, or the struggle for existence, the law of adaptation, or the correspondence of the organism to the changing environment, the transmutation of species, and the genealogical descent of all organic beings, the more complex from the more simple; he nevertheless failed to conceive the selective principle as formulated by Darwin and Wallace, which so admirably complemented these great laws.”[272]
As is well known, Huxley was, if we understand his expressions aright, not fully convinced of the entire adequacy of natural selection.
“There is no fault to be found with Mr. Darwin’s method, then; but it is another question whether he has fulfilled all the conditions imposed by that method. Is it satisfactorily proved, in fact, that species may be originated by selection? that there is such a thing as natural selection? that none of the phenomena exhibited by species are inconsistent with the origin of species in this way?
. . . . . . . . .
“After much consideration, with assuredly no bias against Mr. Darwin’s views, it is our clear conviction that, as the evidence stands, it is not absolutely proven that a group of animals, having all the characters exhibited by species in nature, has ever been originated by selection, whether artificial or natural. Groups having the morphological character of species, distinct and permanent races, in fact, have been so produced over and over again; but there is no positive evidence, at present, that any group of animals has, by variation and selective breeding, given rise to another group which was even in the least degree infertile with the first. Mr. Darwin is perfectly aware of this weak point, and brings forward a multitude of ingenious and important arguments to diminish the force of the objection.”[273]
We have cited the foregoing conclusions and opinions of upwards of forty working biologists, many of whom were brought up, so to speak, in the Darwinian faith, to show that the pendulum of evolutionary thought is swinging away from the narrow and restricted conception of natural selection, pure and simple, as the sole or most important factor, and returning in the direction of Lamarckism.