Premonitions of Biological Evolution.
The eighteenth century had done much to impress the minds of men with an orderly development in sun and planets (Kant and Laplace), in the institutions of human societies (Montesquieu), and in the moral aspirations of mankind (Lessing). Many bold attempts had been made to trace a like orderly development in the physical life of plants and animals (Buffon, Erasmus Darwin, etc.), but neither was the proof cogent nor the process intelligible. Cautious people therefore, and those whose prepossessions inclined them to adopt a very different origin for terrestrial life, held during all this time a position of some strength against speculative philosophers who tried to explain the variety and perfection of living nature by unconscious and unintelligent factors.
About the year 1840 the doctrine of the fixity of species seemed to be victorious. Cuvier's knowledge and skilful advocacy had a few years before over-powered Geoffroy St. Hilaire's conception of a common plan of structure pervading the whole animal kingdom, and the new Philosophie Anatomique was laid on the shelf, side by side with the Philosophie Zoologique of Lamarck, the Zoonomia of Erasmus Darwin, the Théorie de la Terre of Buffon, and the Protogæa of Leibnitz. Yet even then a spectator who was fully informed and at the same time gifted with uncommon foresight might have satisfied himself that the victory of evolution had become inevitable.
Cuvier's memorable descriptions of the extinct vertebrates of the Paris basin had founded the new science of Palæontology, and though neither he nor anyone else was aware of the fact, had made it possible to trace, very imperfectly no doubt, the descent of a few modern ungulates. Lyell's Principles of Geology (1830-3) had shaken the belief in catastrophes repeatedly breaking the succession of life on the earth. It was rapidly becoming impossible to maintain that the account of creation given in the book of Genesis was even approximately accurate. In the year 1828 Baer had almost made up his mind that the facts of development pointed to a common plan of structure, perhaps to a common origin, for each of the great types of animal life.[43] Darwin's Journal had appeared in 1839, and though the explanations which it offered were not inconsistent with prevalent opinion, evolutionary suggestions were introduced into the second edition of 1845. Lyell at least was already aware that the voyage of the Beagle had impelled Darwin to examine afresh the accepted philosophy of creation. Between 1840 and 1850 faint signs of coming change struck orthodox reasoners with misgiving and gave increased confidence to free-thinkers. A few German botanists and zoologists declared against the immutability of species. The Vestiges of the Natural History of Creation, which might be called a premature explosion, dates from 1844. Hofmeister (see supra, p. 109) put forth a detailed comparison of the flowering plants with the higher cryptogams, which strongly suggested a theory of descent with modification, and is unintelligible on any other basis. He indicated no such interpretation himself, being content to establish the new homologies; but the Origin of Species, as soon as it appeared, commanded his entire sympathy.
Among those who rejected fixity of species and special creation before 1859 none was so clear or so outspoken as Herbert Spencer, who thought out for himself an evolutionary philosophy which was not shaken by Darwin. It is impossible to discuss in this place the question whether or not it was shaken by Weismann.
Agassiz's Essay on Classification, which was published in October, 1857, was the last manifesto issued before the Origin of Species by the party which stood out for fixity of species, the last polemic which made De Maillet, Lamarck, and the Vestiges its targets. It is an eloquent but inconsiderate defence of an extreme position. According to Agassiz every branch, class, order, family, genus, and species represents a distinct creative thought; every mark of affinity, every appearance of adaptation to surroundings, has been expressly designed. Extinction and replacement of species are due to the direct intervention of the Creator; pterodactyls are prophetic types of birds, and indicate that divine wisdom had foreseen the possibility of an advance in the organisation of animals which was not immediately practicable; the mallard and scaup duck occur on both sides of the Atlantic because they were simultaneously but separately created in Europe and North America; the teeth of the whale, which never cut the gum, are the result of obedience to a certain uniformity of fundamental structure. Explanations like these removed no difficulties and suggested no inquiries. In the hot debates which ensued the Essay on Classification was rarely mentioned.
[32] Cross and Self-Fertilisation of Plants, chap. xi.
[33] Cuvier did not himself use the word palæontology, which first came in about 1830. In the same way Buffon writes on the history of animals, not on zoology, and on the theory of the earth, not on geology.
[34] This anecdote has also been related in a rather different form.
[35] The same process of "embryonic fission" occurs in other animals also, one of which is a mammal (Praopus).
[36] Linnæus (Fund. Bot. § 134, and Sponsalia Plantarum) gives it as above; Harvey has "Ex ovo omnia"; "ovum esse primordium commune omnibus animalibus," etc.
[37] Harvey need not have gone outside the writings of Aristotle to get the substance of his generalisation. He would have found there that the chief task of both plants and animals is propagation, either by seeds, or eggs, which Aristotle believed to be equivalent to seeds (Hist. anim., VIII., i.; De anim. gen., I., iv.; I., xxiii.). Aristotle excepted the "imperfect animals," such as insects, and the seedless plants, concerning both of which his knowledge was misty and inaccurate; there is no indication that Harvey was better informed.
[38] Hooke figured a thin section of dry cork in his Micrographia (1665), remarking that it was divided into "little boxes or cells." The word cell was suggested by the resemblance of the tissue to a honeycomb; since 1838 it has been thoughtlessly extended from the skeleton to the particle of living matter enclosed within it. Robert Brown (1831) showed that a nucleus is usual in plant-cells; it had been figured by Fontana and others long before. Down to 1838 no results of biological interest followed from the discovery.
[39] Parkinson (1629) speaks of a stove or hothouse, "such as are used in Germany."
[40] The graceful practice of naming genera of plants after benefactors to botany or horticulture was introduced by Father Plumier (1646-1704), who gave the names of L'Obel and Fuchs to the Lobelia and Fuchsia, and whose own name is appropriately borne by the frangipane (Plumeria).
[41] See the account of Cartagena in the Personal Narrative.
[42] See particularly his Essai sur la géographie des plantes (1805).
[43] Baer's expressions are so guarded that his real opinions in 1828 can only be surmised. He never accepted a consistent theory of organic evolution.
PERIOD V
(1859 AND LATER)