II.
An outline of Darwin's personality would not be complete without a glance at some of his mental characteristics, and at his attitude toward religion. Of his intellectual powers, he himself speaks with extraordinary modesty in his autobiography. He points out that he always experienced much difficulty in expressing himself clearly and concisely, but he opines that this very difficulty may have had the compensating advantage of forcing him to think long and intently about every sentence, and thus enabling him to detect errors in reasoning and in his own observations, or in those of others. He disclaimed the possession of any great quickness of apprehension or wit, such as distinguished Huxley. He protested, also, that his power to follow a long and purely abstract train of thought was very limited, for which reason he felt certain that he never could have succeeded with metaphysics or mathematics. His memory, too, he described as extensive, but hazy. So poor in one sense was it that he never could remember for more than a few days a single date or a line of poetry. On the other hand, he did not accept as well founded the charge made by some of his critics that, while he was a good observer, he had no power of reasoning. This, he thought, could not be true, because the "Origin of Species" is one long argument from the beginning to the end, and has convinced many able men. No one, he submits, could have written it without possessing some power of reasoning. He was willing to assert that "I have a fair share of invention, and of common sense or judgment, such as every fairly successful lawyer or doctor must have, but not, I believe, in any higher degree." He adds humbly that perhaps he was "superior to the common run of men in noticing things which easily escape attention, and in observing them carefully."
Writing in the last year of his life, he expressed the opinion that in two or three respects his mind had changed during the preceding twenty or thirty years. Up to the age of thirty or beyond it poetry of many kinds gave him great pleasure. Formerly, too, pictures had given him considerable, and music very great, delight. In 1881, however, he said: "Now for many years I cannot endure to read a line of poetry; I have tried lately to read Shakspeare, and found it so intolerably dull that it nauseated me. I have also almost lost my taste for pictures or music. Music generally sets me thinking too energetically of what I have been at work on, instead of giving me pleasure. I retain some taste for fine scenery, but it does not cause me the exquisite delight which it formerly did." Darwin was convinced that the loss of these tastes was not only a loss of happiness, but might possibly be injurious to the intellect, and more probably to the moral character, by enfeebling the emotional side of one's nature. So far as he could judge, his mind had become in his later years a kind of machine for grinding general laws out of large collections of facts, and that atrophy had taken place in that part of the brain on which the higher aesthetic tastes depend. Curiously enough, however, he retained his relish for novels, and for books on history, biography, and travels.
It is well known that Darwin was extremely reticent with regard to his religious views. He believed that a man's religion was essentially a private matter. Repeated attempts were made to draw him out upon the subject, and some of these were partially successful. Writing to a Dutch student in 1873, he said: "I may say that the impossibility of conceiving that this grand and wondrous universe, with our conscious selves, arose through chance seems to me the chief argument for the existence of God; but whether this is an argument of real value I have never been able to decide. I am aware that if we admit a First Cause, the mind still craves to know whence it came and how it arose. Nor can I overlook the difficulty from the immense amount of suffering through the world. I am also induced to defer to a certain extent to the judgment of the many able men who have fully believed in God; but here again I see how poor an argument this is. The safest conclusion seems to me that the whole subject is beyond the scope of man's intellect; but man can do his duty." To questions put by a German student in 1879, he replied: "Science has nothing to do with Christ, except in so far as the habit of scientific research makes a man cautious in admitting evidence. For myself I do not believe that there ever has been any revelation. As for a future life, every man must judge for himself between conflicting vague probabilities." In the same year he told another correspondent: "In my most extreme fluctuations I have never been an atheist in the sense of denying the existence of a God. I think that generally (and more and more as I grow older), but not always, that an Agnostic would be the more correct description of my state of mind." His latest view is indicated in a letter dated July 3, 1881. Here he expressed the "inward conviction that the universe is not the result of chance." He adds, however: "But, then, with me the horrid doubt always arises whether the convictions of man's mind, which has been developed from the mind of the lower animals, are of any value, or at all trustworthy. Would any one trust the convictions in a monkey's mind, if there are any convictions in such a mind?" The Duke of Argyll has recorded the few words on the subject spoken by Darwin in the last year of his life. The Duke said that it was impossible to look at the wonderful contrivances for certain purposes in nature, and fail to recognize that they were the effect and the expression of mind. Darwin looked at the Duke very hard, and said, "Well, that often comes over me with overwhelming force; but at other times"--here he shook his head vaguely--"it seems to go away."
III.
We pass to a consideration of Darwin's masterworks, the "Origin of Species," the "Variation of Animals and Plants under Domestication," and the "Descent of Man." Before indicating the conclusions reached in the first of these works, we should point out to what extent Darwin had been preceded by dissenters from the belief once almost universally entertained by biologists that species were independently created, and, once created, were immutable. Lamarck was the first naturalist whose divergent views upon the subject excited much attention. In writings published at various dates from 1801 to 1815, he upheld the doctrine that all species, including man, are descended from other species. He pronounced it probable that all changes in the organic, as well as in the inorganic world, were the result of law, and not of miraculous interposition. He seems to have been led to his opinion that the change of species had been gradual by the difficulty experienced in distinguishing species from varieties by the almost perfect gradation of forms in certain groups, and by the analogy of domestic productions. With respect to the means of modification, he attributed something to the direct action of the physical conditions of life, something to the crossing of already existing forms, and much to use and disuse, or, in other words, to the effect of habit. Finally, he held that characters acquired by an existing individual might be transmitted to its offspring.
In 1813 Dr. W.C. Wells read before the Royal Society "An Account of a White Female, Part of whose Skin resembles that of a Negro." In this paper the author distinctly recognized the principle of natural selection, but applied it only to the races of man, and in man only to certain characters. After remarking that negroes and mulattoes enjoy an immunity from certain tropical diseases, he observed, first, that all animals tend to vary in some degree, and, secondly, that agriculturalists improve their domesticated animals by selection. He added that what is done in the latter case by art seems to be done with equal efficacy, though more slowly, by nature in the formation of varieties of mankind fitted for the countries which they inhabit. Again in 1831 Mr. Patrick Matthew published a work on "Naval Timber and Arboriculture," in which he put forth precisely the same view concerning the origin of species as that propounded by Mr. Wallace and by Darwin. Unfortunately for himself, the view was cursorily suggested in scattered passages of an appendix to a work on a different subject, so that it remained unnoticed until Mr. Matthew himself drew attention to it in 1860, after the publication of the "Origin of Species." We observe finally that Mr. Herbert Spencer, in an essay published in 1852, and republished six years later, contrasted the theories of the creation and the development of organic beings. He argued from the analogy of domestic productions, from the changes which the embryos of many species undergo, from the difficulty of distinguishing species and varieties, and from the principle of general gradation, that species have been modified; and he attributed the modification to the change of circumstances.
The two volumes comprising the "Origin of Species" constitute, as the author said, one long argument. It is, of course, impossible in the space at our command to recapitulate in detail even the leading facts and inferences which are brought forward to prove that species have been modified during a long course of descent. We must confine ourselves to a succinct statement of the author's general conclusions. What he undertakes to prove is that the modification of species during a long course of descent has been effected chiefly through the natural selection of numerous successive slight favorable variations, aided in an important manner by the inherited effects of the use and disuse of parts; and in an unimportant manner,--that is, in relation to adaptive structures, whether past or present, by the direct action of external conditions, and by variations which seem to us, in our ignorance, to arise spontaneously. It should be observed that Darwin does not attribute the modification exclusively to natural selection. What he asserts is: "I am convinced that natural selection has been the main, but not the exclusive, means of modification." He submits that a false theory would hardly explain in so satisfactory a manner as does the theory of natural selection the several large classes of facts marshalled in the two volumes now under review. If it be objected that this is an unsafe method of arguing, Darwin rejoins that it is a method usual in judging of the common events of life, and has often been used by the greatest natural philosophers. The undulatory theory of light, for instance, has thus been arrived at; and the belief in the revolution of the earth on its own axis was, until lately, supported by scarcely any direct evidence. It is no valid objection to the Darwinian theory of the origin of species that science as yet throws no light on the far higher problem of the essence or origin of life. Neither has any one explained what is the essence of the attraction of gravity, though nobody now objects to following out the results consequent on this unknown element of attraction.
Why, it may be asked, did nearly all the most eminent naturalists and geologists until recently decline to believe in the mutability of species? Darwin replies that the belief that species were immutable productions was almost unavoidable as long as the history of the world was thought to be of short duration. Even now that we have acquired some idea of the lapse of time, men are too apt to assume without proof that the geological record is so perfect that it would have afforded plain evidence of the mutation of species if they had really undergone mutation. The chief cause, however, of the once-prevalent unwillingness to admit that one species has given birth to other and distinct species is the fact that men are slow to admit great changes of which they do not see the steps. The difficulty is the same which was experienced by many geologists when Lyell first insisted that long lines of inland cliffs had been formed and great valleys excavated, not by catastrophes, but by the slow-moving agencies which we see still at work. The human mind cannot grasp the full meaning of the term of even a million years; cannot add up and perceive the full effects of many slight variations accumulated during an almost infinite number of generations.