The choice was a happy one, for, except by the German zoologist Von Spix, and the botanist Von Martius in 1817-20, and subsequently by Count de Castelnau, no exploration of a region so rich and interesting to the biologist had been attempted. Early in 1848 Bates and Wallace met in London to study South American animals and plants in the principal collections, and afterward went to Chatsworth to gain information about orchids, which they proposed to collect in the moist tropical forests and send home.
On 26th of April, 1848, they embarked at Liverpool in a barque of only 192 tons burden, one of the few ships then trading to Pará, to which seaport of the Amazons region a swift passage, “straight as an arrow,” brought them on 28th of May.
The travellers soon settled in a rocinha, or country-house, a mile and half from Pará, and close to the forest, which came down to their doors. Like other towns along the Amazons, Pará stands on ground cleared from the forest that stretches, a well-nigh pathless jungle of luxuriant primeval vegetation, two thousand miles inland. In that paradise of the naturalist, the collectors gathered consignments which met with ready sale in London, and thus spent a couple of years in pursuits moderately remunerative and wholly pleasurable, till, on reaching Barra, at the mouth of the Rio Negro, one thousand miles from Pará, in March, 1850, Bates and Wallace, who was accompanied by his younger brother, parted company, “finding it more convenient to explore separate districts and collect independently.” Wallace took the northern parts and tributaries of the Amazons, and Bates kept to the main stream, which, from the direction it seems to take at the fork of the Rio Negro, is called the Upper Amazons or the Solimoens. Different in character and climatic conditions from the Lower Amazons, it flows through a “vast plain about a thousand miles in length, and five hundred or six hundred miles in breadth covered with one uniform, lofty, impervious, and humid forest.” Bates stayed in the country till June, 1859, but Wallace left in 1852, and in the following year published an account of his journey under the title of Travels on the Amazon and Rio Negro. That book was written under the serious disadvantage of the destruction of the greater part of the notes and specimens by the burning of the ship in which Mr. Wallace took passage on his homeward voyage. That it remains one of the select company of works of travel for which demand is continuous is evidenced in a reprint which appeared in 1891. If it affords few hints of the author’s bent of mind toward the question of the origin of species, it shows what interest was being aroused within him over the allied subject of the geographical distribution of plants and animals which Mr. Wallace was to make so markedly his own.
In 1854 he sailed for the Malay Archipelago, where nearly eight years were spent in exploring the region from Sumatra to New Guinea. The large and varied outcome of that labour was embodied in numerous papers communicated to learned societies and scientific journals, and in a series of delightful books from The Malay Archipelago, first published in 1869, to Island Life, published in 1880. Among the minor results of his extensive travels—for all else that Wallace did pales before the great discovery which links his name with Darwin’s—was the establishment of a line, known as “Wallace’s,” which divides the Malay Archipelago into two main groups, “Indo-Malaysia and Austro-Malaysia, marked by distinct species and groups of animals.” That line runs through a deep channel separating the islands of Bali and Lombok; the plants and animals on which, although but fifteen miles of water separate them, differ from each other even more than do the islands of Great Britain and Japan. “A similar line, but somewhat farther east, divides on the whole the Malay from the Papuan races of man.”
Among the more fugitive contributions which mark Mr. Wallace’s approach to a solution of the problem in quest of which he and Bates went to the Amazons is a paper On the Law which has Regulated the Introduction of New Species, published in the Annals and Magazine of Natural History, 1855. In this he shows that some form of evolution of one species from another is needed to explain the geological and geographical facts of which examples are given.
In the interesting preface to the reprint of the famous paper On the Tendencies of Varieties to depart Indefinitely from the Original Type, Mr. Wallace recites the several researches which he made in quest of that “form” till, when lying ill with fever at Ternate, in February, 1858, something led him to think of the “positive checks” described by Malthus in his Essay on Population, a book which he had read some years before. Oddly enough, therefore, the honours lie with the maligned Haileybury Reverend Professor of Political Economy in furnishing both Darwin and Wallace with the clue. The “positive checks”—war, disease, famine—Wallace felt must act even more effectively on the lower animals than on man, because of their more rapid rate of multiplication. And he tells us, in the prefatory note to a reprint of his paper, “there suddenly flashed on me the idea of the survival of the fittest, and in the two hours that elapsed before my ague fit was over I had thought out the whole of the theory, and in the two succeeding evenings wrote it out in full and sent it by the next post to Mr. Darwin,” asking him, if he thought well of the essay, to send it to Lyell. This Darwin did with the following remarks: “Your words have come true with a vengeance—that I should be forestalled.... I never saw a more striking coincidence; if Wallace had my MS. sketch written out in 1842, he could not have made a better short abstract! Even his terms now stand as heads of my chapters. Please return me the MS., which he does not say he wishes me to publish; but I shall, of course, at once write and offer to send to any journal. So all my originality, whatever it may amount to, will be smashed, though my book, if it will ever have any value, will not be deteriorated, as all the labour consists in the application of the theory.” Darwin came out well in this business. For to have hit upon a theory which interprets so large a question as the origin and causes of modification of life-forms; to keep on turning it over and over again in the mind for twenty long years; to spend the working hours of every day in collection and verification of facts for and against it; and then to have another man launching a “bolt from the blue” in the shape of a paper with exactly the same theory, might well disturb even a philosopher of Darwin’s serenity.
However, both Hooker and Lyell had read his sketch a dozen years before, and it was arranged by them, not as considering claims of priority, which have too often been occasion of unworthy wrangling, but in the “interests of science generally,” that an abstract of Darwin’s manuscript should be read with Wallace’s paper at a meeting of the Linnæan Society on the 1st of July, 1858. The full title of the joint communication was On the Tendency of Species to form Varieties, and on the Perpetuation of Varieties and Species by Natural Selection. Sir Joseph Hooker, describing the gathering, says that “the interest excited was intense, but the subject was too novel and too ominous for the old school to enter the lists before armouring. After the meeting it was talked over with bated breath. Lyell’s approval, and perhaps, in a small way mine, as his lieutenant in the affair, rather overawed the Fellows, who would otherwise have flown out against the doctrine. We had, too, the vantage ground of being familiar with the authors and their theme.” Nothing can deprive Mr. Wallace of the honour due to him as the co-originator of the theory, which, regarded in its application to the origin, history, and destiny of man, involves the most momentous changes in belief, and there may be fitly quoted here his own modest and, doubtless, correct, assessment of limitations which in no wise invalidate his high claims. In the Preface to his Contributions to the Theory of Natural Selection (1870), Mr. Wallace says the book will prove that he both saw at the time the value and scope of the law which he had discovered, and has since been able to apply to some purpose in a few original lines of investigation. “But,” he adds, “here my claims cease. I have felt all my life, and I still feel, the most sincere satisfaction that Mr. Darwin had been at work long before me, and that it was not left for me to attempt to write the Origin of Species. I have long since measured my own strength, and know full well that it would be quite unequal to that task. Far abler men than myself may confess that they have not that untiring patience in accumulating, and that wonderful skill in using, large masses of facts of the most varied kind—that wide and accurate physiological knowledge—that acuteness in devising and skill in carrying out experiments, and that admirable style of composition at once clear, persuasive, and judicial—qualities which, in their harmonious combination, mark out Mr. Darwin as the man, perhaps of all men now living, best fitted for the great work he has undertaken and accomplished.”
In a letter to Wallace dated 20th April, 1870, Darwin says, “There has never been passed on me, or, indeed, on any one, a higher eulogium than yours. I wish that I fully deserved it. Your modesty and candour are very far from new to me. I hope it is a satisfaction to you to reflect—and very few things in my life have been more satisfactory to me—that we have never felt any jealousy towards each other, though in one sense rivals. I believe I can say this of myself with truth, and I am absolutely sure it is true of you.”
But on one question, and that round which discussion still rages, the friends were poles asunder. There had been correspondence between them as to the bearing of the theory of natural selection on man, and in April, 1869, Darwin wrote, “As you expected, I differ grievously from you, and I am very sorry for it. I can see no necessity for calling in an additional and proximate cause in regard to man.” In the fifteenth chapter of his comprehensive book on Darwinism, Wallace admits the action of natural selection in man’s physical structure. This structure classes him among the vertebrates; the mode of human suckling classes him among the mammals; his blood, his muscles, and his nerves, the structure of his heart with its veins and arteries, his lungs and his whole respiratory and circulatory systems, all closely correspond to those of other mammals, and are often almost identical with them. He possesses the same number of limbs, terminating in the same number of digits, as belong fundamentally to the mammals. His senses are identical with theirs, and his organs of sense are the same in number and occupy the same relative position. Every detail of structure which is common to the mammalia as a class is found also in man, while he differs from them only in such ways and degrees as the various species or groups of mammals differ from each other. He is, like them, begotten by sexual conjugation; like them, developed from a fertilized egg, and in his embryonic condition passes through stages recapitulating the variety of enormously remote ancestors of whom he is the perfected descendant. Full-grown, he appears as most nearly allied to the anthropoid or man-like apes; so much does his skeleton resemble theirs that, comparing him with the chimpanzee, we find, with very few exceptions, bone for bone, differing only in size, arrangement, and proportion.
Mr. Wallace, therefore, rejected the idea of man’s special creation “as being entirely unsupported by facts, as well as in the highest degree improbable.” But he would not allow that natural selection explains the origin of man’s spiritual and intellectual nature. These, he argues, “must have had another origin, and for this origin we can only find an adequate cause in the unseen universe of Spirit.” More detailed treatment of this argument will be given further on; here reference is made to it as furnishing the explanation why Mr. Wallace kept not his “first estate,” and dropped out of the ranks of Pioneers of Evolution. Many subjects, as hinted above, have occupied his facile pen—land nationalization, causes of depression in trade, labourers’ allotments, vaccination, et hoc genus omne; showing, at least, the prominence which all social matters occupy in the minds of the leading exponents of the theory of Evolution. For of this, as will be seen, both Herbert Spencer and Huxley supply cogent examples in their application of that theory to human interests. But it is as a defender, although on lines of his own not wholly orthodox, of supernaturalism, with attendant beliefs in miracles and the grosser forms of spiritualism, that Mr. Wallace appears in the character of opponent to the inclusion of man’s psychical nature as a product of Evolution.