KINETOGENESIS, in evolution, the mechanical process of a transformation of parts, especially parts belonging to the internal skele ton, skull and limbs, is very ingeniously inter preted by Cope as having been accomplished in mammals through the agency molar motions, use and food. The motion itself is neo-Lamarckian. Cope's proposal (it was he who brought the term into existence) is to °cite examples of the direct modifying effect of external influ ences on the characters of individual animals and plants.* The influences which thusplay a part in evolution fall into two classes. They are either physicochemical, or molecular; or, they are mechanical, or molar. A gradual transformation of the parts of an organism is supposed by Cope to be the result of these influences. The two types of influence which thus express themselves in evolution, Cope calls Physiogenesis, which operates through molecu lar action; and Kinetogenesis, which expresses itself as molar motion. Cope has likewise traced the line of progression in fossil genera as exemplified by numerous series of inter mediate forms. But Herbert Spencer also con tributed much in this direction by his theory of the mechanical origin of the segmentation of the body in vertebrates, leading (as he thought) to the formation of vertebra.
This term suggested by E. D. Cope, meaning development by motion, or the exercise of parts or organs, is nearly the equivalent of use (q.v.). The examples given by Cope are the develop ment by use of muscles of any hard parts or bone. He claims that muscular tissue is highly plastic, and since it is directly con trolled by nervous or equivalent stimuli, °the effect of the latter in building structure is evi dent.* Another example, overlooked by late students, is the beautiful study on the mechan ical genesis of bone structure published by Wyman in 1857. This anatomist shows that the cancellated structure of the hone (see BONE) in the lumbar vertebra, the thigh-bone, tibia, as tragalus and os calcis of man is peculiar to him, and has °a definite relation to the erect position which is naturally assumed by man alone.* The fibres or cancelli of such bones as assist in supporting the weight °are arranged either in the direction of that weight, or in such a man ner as to support and brace those cancelli which are in that direction. In a mechanical point of view they may be regarded in nearly all these bones as a series of studs and braces.* Wyman dealing with the individual bones shows in what direction force or weight is applied to them, and the corresponding direction the cancelli assume. On the lumbar vertebra there is vertical pres sure, and the principal bone fibres within are also vertical. On the neck of the thigh bone the weight of the body is applied obliquely to the end of an arm, °within it there is a com bination of fibres giving strength with lightness, which forms a frame mechanically adapted for resisting the weight which rests upon it," and so with the astragalus. °A certain direction of fibres in all these instances co-exists with a certain direction, or certain directions, of the transmission of pressure. From this constant association of structures and function the in ference seems unavoidable, that they are means and ends.*
Comparing the bones in question with those of the gorilla and chimpanzee, only °slight traces of the trusswork described in man ex ist* As they practically exist in man alone, Wyman maintains that practically relate to the kind of locomotion which he alone of the whole ani mal series can be said to possess, namely, that of walking erect, and which requires in the pas sive and resting organs subservient to it, in order that it may be effected with ease and grace, a nice combination of lightness with strength in the materials. His attitude more than any other, in consequence of the pillars of support being arranged in vertical planes, requires the most effectual means for counter acting shocks.* Cope's contributions to this subject in the way of materials drawn from fossil vertebrates are extensive and weighty. He, and also Ry der, have discussed the molding of the limb joints as the result of mechanical strains; also the origin of the teeth, through mechanical strains or impacts.. Thus the origin of the canine, pseudo-canine and canine-like incisor • teeth °is due to the strains sustained by them on account of their position in the jaws at points which are naturally utilized in the seizing of prey, or the fighting of enemies.* For example the greatly increased size of the canine teeth of the walrus is due to the use of these teeth in the breaking of ice, and in climbing from the water upon the edge of the floe ice. It is so, adds Cope, with the straight incisors of the hippopotamus, °use as diggers has straightened them to a horizontal from their primitive ver tical direction, a change which is also partially accomplished in the true pigs (Sus).* The molar teeth owe their increased diam eters to much more severe direct irritation and impact. The origin of the sectorial or shear like molar teeth of the cat, lion and other carnivora is thus explained by Cope: °The specialization of one tooth to the exclusion of others as a sectorial appears to be due to the following causes: It is to be observed in the first place that when a carnivore devours a carcass, it cuts off masses with its sectorials, using them as shears. In so doing it brings the part to be divided to the angle or canthus of the soft walls of the mouth, which is at the front of the masseter muscle. At this point the greatest amount of force is gained, since the weight is thus brought immediately to the power, which would not be the case were the sectorial situated much in front of the mas seter. On the other hand, the sectorial could not be situated farther back, since it would then he inaccessible to a carcass or mass too large to be taken into the mouth.* The great length and chisel-like incisor teeth of the squirrel and other rodents also illustrate this subject. Their progressive lengthening through exercise has been explained by Ryder, who shows that the mechanical action involving backward pressure is precisely the opposite of that which has occurred to the carnivora, where the pressure has always been forward owing to the development of the canines.