In our author’s next chapter, the twelfth of the series, he proceeds to examine the “Lamarckian hypothesis of the origin of plants, and its consequences.”
In his thirteenth chapter, on “The two Floras, marine and terrestrial,” he has shown that all our experience is opposed to the opinion, that the one has been transmuted into the other. If the marine had been converted into terrestrial vegetation, we ought to have, in the Lake of Stennis, for example, plants of an intermediate character between the algæ of the sea, and the monocotyledons of the lake. But no such transition-plants are found. The algæ, as our author observes, become dwarfish and ill-developed. They cease to exist as the water becomes fresher, “until at length we find, instead of the brown, rootless, flowerless fucoids and confervæ of the ocean, the green, rooted, flowering flags, rushes, and aquatic grasses of the fresh water. Many thousands of years have failed to originate a single intermediate plant.” The same conclusion may be drawn from the character of the vegetation along the extensive shores of Britain and Ireland. No botanist has ever found a single plant in the transition state.
The fourteenth chapter of the “Footprints” will be perused with great interest by the general reader. It is a powerful and argumentative exposure of the development hypothesis, and of the manner in which the subject has been treated in the “Vestiges.” Whether we consider it in its nature, in its history, or in the character of the intellects with whom it originated, or by whom it has been received and supported, Mr. Miller has shown that it has nothing to recommend it. It existed as a wild dream before Geology had any being as a science. It was broached more than a century ago by De Maillet, who knew nothing of the geology even of his day. In a translation of his Telhamed, published in 1750, Mr. Miller finds very nearly the same account given of the origin of plants and animals, as that in the “Vestiges,” and in which the sea is described as that “great and fruitful womb of nature, in which organization and life first begin.” Lamarck, though a skilful botanist and conchologist, was unacquainted with geology; and as he first published his development hypothesis in 1802, (an hypothesis identical with that of the “Vestiges,”) it is probable that he was not then a very skilful zoologist. Nor has Professor Oken any higher claims to geological acquirements. He confesses that he wrote the first edition of his work in a kind of inspiration! and it is not difficult to estimate the intelligence of the inspiring idol that announced to the German sage that the globe was a vast crystal, a little flawed in the facets, and that quartz, feldspar, and mica, the three constituents of granite, were the hail-drops of heavy showers of stone that fell into the original ocean, and accumulated into rocks at the bottom!
Such is the unscientific parentage of the theories promulgated in the “Vestiges.” But the author of this work appeals in the first instance to science. Astronomy, Geology, Botany, and Zoology are called upon to give evidence in his favor; but the astronomer, geologist, botanist, and the zoologist, all refuse him their testimony, deny his premises, and reject his results. “It is not,” as Mr. Miller happily observes, “the illiberal religionist that casts him off. It is the inductive philosopher.” Science addresses him in the language of the possessed: “The astronomer I know, and the geologist I know; but who are ye?” Thus left alone in a cloud of star-dust, or in brackish water between the marine and terrestrial flora, he “appeals from science to the want of it,” casts a stone at our Scientific Institutions, and demands a jury of “ordinary readers,” as the only “tribunal” by which “the new philosophy is to be truly and righteously judged.”
The last and fifteenth chapter of Mr. Miller’s work, “On the Bearing of Final Causes on Geologic History,” if read with care and thought, will prove at once delightful and instructive. The principle of final causes, or the conditions of existence, affords a wide scope to our reason in Natural History, but especially in Geology. It becomes an interesting inquiry, if any reason can be assigned why at certain periods species began to exist, and became extinct after the lapse of lengthened periods of time, and why the higher classes of being succeeded the lower in the order of creation? The incompleteness of geological science, however, does not permit us to remove, for the present, the veil which hangs over this mysterious chronology; but our author is of opinion that in about a quarter of a century, in a favored locality like the British Islands, geological history “will assume a very extraordinary form.”
It is a singular fact, which will yet lead to singular results, that Cuvier’s arrangement of the four classes of vertebrate animals should exhibit the same order as that in which they are found in the strata of the earth. In the fish, the average proportion of the brain to the spinal cord is only as 2 to 1. In the reptile, the ratio is 2½ to 1. In the bird, it is as 3 to 1. In the mammalia, it is as 4 to 1; and in man, it is as 23 to 1. No less remarkable is the fœtal progress of the human brain. It first becomes a brain resembling that of a fish; then it grows into the form of that of a reptile; then into that of a bird; then into that of a mammiferous quadruped, and finally it assumes the form of a human brain, “thus comprising in its fœtal progress an epitome of geological history, as if man were in himself a compendium of all animated nature, and of kin to every creature that lives.”
With these considerations, Mr. Miller has brought his subject to the point at which Science in its onward progress now stands. It is to embryology we are in future to look for further information upon the most intimate relations which exist between all organized beings. We may fairly entertain the hope that the time is not far when we shall not only fully understand the Plan of Creation, but even lift some corner of the veil which has hitherto prevented us from forming adequate ideas of the first introduction of animal and vegetable life upon earth, and of the changes which both kingdoms have undergone in the succession of geological ages.
L. AGASSIZ.
Cambridge, September, 1850.