The order of events then is: first, increased and altered muscular function; second, growth of bones and adjustment; third, binding together of these by new or modified ligaments. If it were possible to separate in this way the age-long formation of such a living tool as the human foot, this is the order in which alone, I submit, the sequence of events can be placed. It is a convenient, because simple and plain example of initiative in evolution, and I cannot say how much I owe to Professor Keith’s teaching on the subject.[71]
CHAPTER XXII.
MUSCLES.
A work of great value to the biologist has been written by one whose work has led him in the widening path of human physiology and its very title is instinct with meaning. The Integrative action of the Nervous System may not aid the systematist or the student of genetics, but for insight into formative powers, where the former can but record facts and find no interpretation, such a work is of supreme importance. When the plant sealed its fate and enclosed itself in a cell-wall and abandoned a life of movement, it was foreordained that its rival would be that cell and its descendants which could adopt a free life, and that the future of the world would lie at the proud foot of that conqueror who could command and mobilize the resources of a nervous system. And, as we know, it has fallen to man to receive the rewards of this promise and potency of a higher life. If one seeks to understand the steps by which man has arrived at his primacy it can only be by the highway of nervous progress, however much the tracing of certain connecting or collateral paths may throw light on contributing causes. So that man’s place in Nature is nearly synonymous with the structural evolution of his brain, as Huxley has shown in his clear and simple manner. Even if man is to remain still an animal Melchisedec for generations to come, or to put it lower, a foundling, no future discoveries that can be imagined will disprove Huxley’s declaration, “Evolution is no longer an hypothesis, but an historical fact.” And yet if man has become adapted to his world, and, in it, crowned with glory and honour by the unfolding of some original complexity, or as the result of some fortunate mutations in the distant past, the human brain, with its cranial capacity of nearly three times the number of cubic centimetres to that of the gorilla, has been making false claims to a paramountcy over all factors in the wonderful initiative of fresh capacities and their mobilisation for conquest. Nothing less than such a “claim” was understood by the ancients, and, though metaphysics had to supply the lack of anatomy and physiology, it has always been held that mind was lord of matter, and now scientific research has told us why. But no one, even the most hard-shelled scholastic, can refuse to the brain organ its predominant share in the making of man. This is seen even in the frigid sphere of science by the difference of interest there is shown between any great discovery bearing on the evolution of man, or on some new lower animal form. When Sir. H. H. Johnston astonished zoologists in 1901 by his discovery and proof of the existence of an archaic large mammal which had been interned for an incalculable time in the Semliki Forest, the thrill felt at that historic meeting passed off very soon when the leading British biologist had monographed the Okapi, settled its name and surname and introduced it into text-books. This is never the fate of such as Pithecanthropus or Eoanthropus dawsoni, or of the more recent genealogical theory and researches as to arboreal man. The call of these studies of man’s evolution is felt by all, and the difference in the two branches of biology may account for what must have struck many others, that is the neglect of adding the blue ribbon of science to the honours of the discoverer of the Okapi.
These few trite remarks as to the importance of the nervous system in the making of man have been introduced here, though they bear more closely on the next two chapters, because this importance comes in at every stage of the present treatment of the origin of modifications in muscle.
Anatomists’ Views of Muscles.
There is a very strict and austere custom among anatomists, which doubtless is in a measure necessary, of insisting upon following rigorously the homologies of muscles, especially in human anatomy, and in this branch of a greater subject the canons are followed to an extent that surprises the seeker after origins. A remarkable example of this is in a paper by an eminent anatomist, now Professor at King’s College, Dr. E. Barclay Smith. It is a paper on the “Morphology of the short extensor of the human fingers.”[72] He says “the precise significance of this occasional extensor brevis digitorum manus is a matter of considerable interest.” He gives four possible interpretations of this unusual muscle. The last, viz., that it is derived from a new muscle-germ alone interests us here because of the remarkable caution and austerity of his remarks on this interpretation. “If an ext. brevis dig. manus cannot be regarded as an atavistic anomaly, or as a derivative from any existing musculature, the only way in which its presence can be accounted for is to suppose that it is of entirely new origin—the product of a new muscle-germ. Such an explanation is, of course, the last resort, and all other possible derivations must be disproved before it can be accepted.” The physiologist would probably think such an interpretation was the obviously first resort. The same writer discusses at length the homology of an exceedingly rare anomaly among muscles, the extensor ossis metacarpi hallucis, and his desire on the one hand to find a missing parent for Japhet, and his honesty and accuracy on the other hand lead him to say “even when it is present, it cannot be regarded as directly atavistic, since it does not represent a normal mammalian tendency.” And he adds a gentle but remote suggestion—“Brooks certainly describes such a muscle in menobranchus and hatteria—two rare and remote reptiles!” But, lawful and necessary though this be, there must be stages on the path of human evolution where such a method must fail and the anatomists can do no more than hold aloof from theory or speculation, with a certain grim enjoyment of the disputes and difficulties of the genealogists.
Initiative in Muscles.
Initiative in the evolution of muscles clearly occurs somewhere in the stem, and behind the formed expression of an altered habit is the integrating action of the nervous system. This will be by some looked at askance as a deus ex machinâ and reckoned as part of the argument from ignorance in a way which recalls Weismann’s scorn of Lamarckian factors in germinal selection. I submit that what he and Osborn call “the unknown factor” of use and habit, arising in response to new stimuli meets as no other proposed suggestion does the formation of new muscles. Given a certain fundamental architecture of skeleton and musculature, such as of primitive vertebrates, one can, without doing violence to any known facts, place the formation of new organs of movement in the following order:—