The most complex animal proceeds originally from a simple cell; and 'at the two extremes we may contemplate the single germinal membrane of the ovum, which is discharging contemporaneously every function—digesting, absorbing, respiring, etc.; and the complete organic apparatus of man, the stomach, the lungs, the skin, the kidneys, and the liver—mechanisms set apart each for the discharge of a special duty, yet each having arisen, as we know positively from watching the order of their development, from that simple germinal membrane.' (Draper.) This is what one physiologist says of the ovum which is being developed into a complex being. Here is what another says of animals at the lower end of the zoological scale: 'The simplest organisms breathe, exhale, secrete, absorb, and reproduce, by their envelopes alone.' (Lewes.) Here we perceive the resemblance between the ovum of the higher animals and the permanent structure of the lower animals. Indeed, some of the lower forms of animal life are simply cells. How vast the difference between the organism of man, with all its complexity of structure, and that of the Ameba or Actinophrys, which, being merely a homogeneous mass of organic matter, performs all the functions of its simple life without any special organ whatever! Yet, is man any less a unit than the Ameba, or any other simple organism? Does his multiplicity of organs impair the integrity of his anatomical and physiological oneness? Is the circulation independent of respiration? Is digestion independent of the circulation? Can any one organ act independently of the others? Is not the entire series of parts, organs, and functions bound up in complete and inseparable unity? The vicarious action of one organ for another has been a question among physiologists; and if admitted, as in the case of the salivary glands acting for the kidneys in profuse spitting, and the skin for the liver, the vicarious function can only obtain to a slight degree and in a temporary manner. The destruction of any considerable organ involves the destruction of all the rest. I repeat that the integrity of the physiological unity at the top of the scale, is far more complete, with all its complexity, than is the integrity of the physiological unity at the bottom of the scale, with its marked simplicity of structure. By no sort of legerdemain or surgical skill can we make an individual mammal become two. If we divide it, the whole dies. Not so, however, with some of the lower grades of animal existence. Cut a hydra into thirty or forty pieces, and each piece will become a distinct animal—a facsimile of the original one. In quite an analogous way do a large number of animals at the lower end of the scale propagate, by segmentation and division; one individual becoming two, two four, and so on.
Many examples might be adduced to show the absence of organized unity in the lower orders of the animal creation. Thus, in the annelid, which is composed of a great many similar rings, and is regarded as quite a complex creature, there is so little dependence of one part on another, that a number of the rings may be destroyed without any injury to the rest. The Synapta, when in want of food, will amputate its own body to procure the necessary supply; and it has been observed to repeat the operation, until it 'had by degrees eaten away the whole of its body to keep life in the head.' (Quatrefages.) Such a phenomenon as this is very unlike that presented by the higher animals, which, together with their multiplied individuality of part and function, and their infinite variety of physiognomic expression, present, at the same time, a unity of organization so complete, that an injury to one part is instantaneously telegraphed to all parts of the system, and sympathized in by all to a greater or less extent.
As in physiology, the development of the individual corresponds to the development of the entire zoological series; so, when we rise into the psychological realm, do we ascertain that the development of the individual mind corresponds to the development of the mental series from the savage to the civilized. In the physiognomy of the savage there is little variety of expression; he has not differentiated that multiplicity of thought and feeling which moulds the face and plays upon its lineaments in the cultivated Teuton. The same is true of the latter while an infant. But who will say that the cultured man of this age is less a balanced, unitized creature than the child of the cradle, or of the forest? The latter is but a creature of impulse, moved by every appetite, and swayed by every gust of passion. He has no fixed principles for the regulation of his life. There is no presiding power to rule and subordinate the tumultuous and refractory elements of his character, and thus unitize the mental organism and its manifestations. This is what culture gives. Here then we also perceive that with the development of variety and complexity, the element of unity becomes more active and manifest. This view of the progressive unitization of the individual man in a psychological aspect, is very suggestive when taken in connection with the wane of despotism and the growth of liberty, as society and government advance, and it becomes ever less the province of law to govern, and also to regulate.
We have adduced some of the illustrations which physical and physiological science affords of the Law of Universal Development: let us close this part of our subject with the illustrations afforded by the rise and progress of Science as a whole. The first germs of science were very simple, existing in connection with Art, and subserving the purposes of priestcraft. For a long time the range of scientific inquiry was so limited that the same individual was able to grasp it entire. But one branch after another has sprung up, diverging more and more into the realms of the unknown, until no one mind can hope to obtain even a general knowledge of them all.
But this has not been the only tendency of scientific growth. Divergence and differentiation had not proceeded far till the combining and organizing movement began. The more individuality and complexity have threatened to outreach the mental powers and become unmanageable, the more have order and organization shown their ability to subordinate and unitize the seeming diversity of elements. While the sciences continued to increase in number and complexity, they began to overlap and interlace, the principles of one running into the domain of another, and even coördinating and binding together its seemingly incongruous parts.
A simple scientific generalization is based on certain facts which, taken in their collective capacity, mean the truth which is expressed in the formula. A higher generalization embraces those which are simpler, and unites by its expression the truths which they contain into the formula of one great truth. This process goes on, rising constantly higher and higher, the generalizations of the ascending series becoming more comprehensive, and the convergence of all the diversified elements into great general laws more striking and complete. Thus advances the unitizing movement of science; and it is now progressing with a steadiness and certainty unknown in former periods of research. Great minds are at this moment occupied in the discovery and verification of these great unitizing laws. Thus we perceive, that while science has developed a bewildering mass of individual facts and minor principles, it has also developed the germs of a unity which is destined to unfold with a richness and magnificence of result heretofore unknown in the annals of human inquiry.
As the special departments of science have testified, so also does the general view of all science testify to this Law of Universal Development.
But, what has all this to do with American Destiny? Very much, as may yet appear. It is by the Past only that we can read the Future; and if in history and in all development, there is revealed by the inductive process a great general law, that law becomes the Oracle of Destiny.
A fitting transition from science to history would be ethnology, the science of races, connected as it is with physics, chemistry, and physiology, on the one hand, and with history on the other.
There are different theories in vogue to account for the diversity of human races now in existence. Some refer human origin to an original pair, whose descendants have changed through the action of physical causes, as food, soil, climate, and scenery, and also through the operation of moral ones as dependent on the physical, and therefore secondary thereto, such as manners, customs, and government. Others deduce it from different lines of development, coming up through the zoological scale, and thence passing from the lower to the higher races of men. Others still speak of mankind as originating 'in nations,' each race being fixed in its physical and mental characteristics, and having an origin independent and distinct from all others.