We can probably best illustrate the opinions of Americans on the question of evolution just before the appearance of Darwin’s great work by directing attention to James D. Dana’s Thoughts on Species (24, 305, 1857). After reading this article and others of a similar nature by Agassiz, one comes to the opinion that unconsciously both men are proving evolution, but consciously they are firm creationists. It is astonishing that with their extended and minute knowledge of living organisms and their philosophic type of mind neither could see the true significance of the imperceptible transitions between some species, which if they do not actually pass into, at least shade towards, one another.
Dana speaks of “the endless diversities in individuals” that compose a species, and then states that a living species, like an inorganic one, “is based on a specific amount or condition of concentered force defined in the act or law of creation.” Species, he says, are permanent, and hybrids “cannot seriously trifle with the true units of nature, and at the best, can only make temporary variations.” “We have therefore reason to believe from man’s fertile intermixture, that he is one in species: and that all organic species are divine appointments which cannot be obliterated, unless by annihilating the individuals representing the species.”
Through the activities of the French the world was prepared for the reception of evolution, and now it was already in the minds of many advanced thinkers. In 1860 Asa Gray sent to the editor of the Journal (29, 1) an article by the English botanist, Joseph D. Hooker, entitled “On the Origination and Distribution of Species,” with these significant remarks:
“The essay cannot fail to attract the immediate and profound attention of scientific men.... It has for some time been manifest that a re-statement of the Lamarckian hypothesis is at hand. We have this, in an improved and truly scientific form, in the theories which, recently propounded by Mr. Darwin, followed by Mr. Wallace, are here so ably and altogether independently maintained. When these views are fully laid before them, the naturalists of this country will be able to take part in the interesting discussion which they will not fail to call forth.”
Hooker took up a study of the flora of Tasmania, of which the above cited article is but a chapter, with a view to trying out Darwin’s theory, and he now accepts it. He says, “Species are derivative and mutable.” “The limits of the majority of species are so undefinable that few naturalists are agreed upon them.”
Asa Gray had received from Darwin an advance copy of the book that was to revolutionize the thought of the world, and at once wrote for the Journal a Review of Darwin’s Theory on the Origin of Species by means of Natural Selection (29, 153, 1860). This is a splendid, critical but just, scientific review of Darwin’s epoch-making book. Evidently views similar to those, of the English scientist had long been in the mind of Gray, for he easily and quickly mastered the work. He is easy on Dana’s Thoughts on Species, which were idealistic and not in harmony with the naturalistic views of Darwin. On the other hand, he contrasts Darwin’s views at length with those of the creationists as exemplified by Louis Agassiz, and says “The widest divergence appears.”
Gray says in part:
“The gist of Mr. Darwin’s work is to show that such varieties are gradually diverged into species and genera through natural selection; that natural selection is the inevitable result of the struggle for existence which all living things are engaged in; and that this struggle is an unavoidable consequence of several natural causes, but mainly of the high rate at which all organic beings tend to increase.
Darwin is confident that intermediate forms must have existed; that in the olden times when the genera, the families and the orders diverged from their parent stocks, gradations existed as fine as those which now connect closely related species with varieties. But they have passed and left no sign. The geological record, even if all displayed to view, is a book from which not only many pages, but even whole alternate chapters have been lost out, or rather which were never printed from the autographs of nature. The record was actually made in fossil lithography only at certain times and under certain conditions (i.e., at periods of slow subsidence and places of abundant sediment); and of these records all but the last volume is out of print; and of its pages only local glimpses have been obtained. Geologists, except Lyell, will object to this,—some of them moderately, others with vehemence. Mr. Darwin himself admits, with a candor rarely displayed on such occasions, that he should have expected more geological evidence of transition than he finds, and that all the most eminent paleontologists maintain the immutability of species.
The general fact, however, that the fossil fauna of each period as a whole is nearly intermediate in character between the preceding and the succeeding faunas, is much relied on. We are brought one step nearer to the desired inference by the similar ‘fact,’ insisted on by all paleontologists, that fossils from two consecutive formations are far more closely related to each other, than are the fossils of two remote formations.