a history of science-4-第30章
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urrent belief with that class of humanity who accept almost any statement as true that harmonizes with their prejudices without realizing its implications。
Thus it is recorded with eclat that the discovery of the close proximity of America at the northwest with Asia removes all difficulties as to the origin of the Occidental faunas and floras； since Oriental species might easily have found their way to America on the ice； and have been modified as we find them by 〃the well…known influence of climate。〃 And the persons who gave expression to this idea never dreamed of its real significance。 In truth； here was the doctrine of evolution in a nutshell； and； because its ultimate bearings were not clear； it seemed the most natural of doctrines。 But most of the persons who advanced it would have turned from it aghast could they have realized its import。 As it was； however； only here and there a man like Buffon reasoned far enough to inquire what might be the limits of such assumed transmutation； and only here and there a Darwin or a Goethe reached the conviction that there are no limits。
LAMARCK VERSUS CUVIER
And even Goethe and Darwin had scarcely passed beyond that tentative stage of conviction in which they held the thought of transmutation of species as an ancillary belief not ready for full exposition。 There was one of their contemporaries； however； who； holding the same conception； was moved to give it full explication。 This was the friend and disciple of Buffon； Jean Baptiste de Lamarck。 Possessed of the spirit of a poet and philosopher； this great Frenchman had also the widest range of technical knowledge； covering the entire field of animate nature。 The first half of his long life was devoted chiefly to botany； in which he attained high distinction。 Then； just at the beginning of the nineteenth century； he turned to zoology； in particular to the lower forms of animal life。 Studying these lowly organisms； existing and fossil； he was more and more impressed with the gradations of form everywhere to be seen； the linking of diverse families through intermediate ones； and in particular with the predominance of low types of life in the earlier geological strata。 Called upon constantly to classify the various forms of life in the course of his systematic writings； he found it more and more difficult to draw sharp lines of demarcation； and at last the suspicion long harbored grew into a settled conviction that there is really no such thing as a species of organism in nature； that 〃species〃 is a figment of the human imagination； whereas in nature there are only individuals。
That certain sets of individuals are more like one another than like other sets is of course patent； but this only means； said Lamarck； that these similar groups have had comparatively recent common ancestors； while dissimilar sets of beings are more remotely related in consanguinity。 But trace back the lines of descent far enough； and all will culminate in one original stock。 All forms of life whatsoever are modified descendants of an original organism。 From lowest to highest； then； there is but one race； one species； just as all the multitudinous branches and twigs from one root are but one tree。 For purposes of convenience of description； we may divide organisms into orders； families； genera； species； just as we divide a tree into root； trunk； branches； twigs； leaves； but in the one case； as in the other； the division is arbitrary and artificial。
In Philosophie Zoologique （1809）； Lamarck first explicitly formulated his ideas as to the transmutation of species； though he had outlined them as early as 1801。 In this memorable publication not only did he state his belief more explicitly and in fuller detail than the idea had been expressed by any predecessor； but he took another long forward step； carrying him far beyond all his forerunners except Darwin； in that he made an attempt to explain the way in which the transmutation of species had been brought about。 The changes have been wrought； he said； through the unceasing efforts of each organism to meet the needs imposed upon it by its environment。 Constant striving means the constant use of certain organs。 Thus a bird running by the seashore is constantly tempted to wade deeper and deeper in pursuit of food； its incessant efforts tend to develop its legs； in accordance with the observed principle that the use of any organ tends to strengthen and develop it。 But such slightly increased development of the legs is transmitted to the off spring of the bird； which in turn develops its already improved legs by its individual efforts； and transmits the improved tendency。 Generation after generation this is repeated； until the sum of the infinitesimal variations； all in the same direction； results in the production of the long…legged wading…bird。 In a similar way； through individual effort and transmitted tendency； all the diversified organs of all creatures have been developedthe fin of the fish； the wing of the bird； the hand of man； nay； more； the fish itself； the bird； the man； even。 Collectively the organs make up the entire organism； and what is true of the individual organs must be true also of their ensemble； the living being。
Whatever might be thought of Lamarck's explanation of the cause of transmutationwhich really was that already suggested by Erasmus Darwinthe idea of the evolution for which he contended was but the logical extension of the conception that American animals are the modified and degenerated descendants of European animals。 But people as a rule are little prone to follow ideas to their logical conclusions； and in this case the conclusions were so utterly opposed to the proximal bearings of the idea that the whole thinking world repudiated them with acclaim。 The very persons who had most eagerly accepted the idea of transmutation of European species into American species； and similar limited variations through changed environment； because of the relief thus given the otherwise overcrowded ark； were now foremost in denouncing such an extension of the doctrine of transmutation as Lamarck proposed。
And； for that matter； the leaders of the scientific world were equally antagonistic to the Lamarckian hypothesis。 Cuvier in particular； once the pupil of Lamarck； but now his colleague； and in authority more than his peer； stood out against the transmutation doctrine with all his force。 He argued for the absolute fixity of species； bringing to bear the resources of a mind which； as a mere repository of facts； perhaps never was excelled。 As a final and tangible proof of his position； he brought forward the bodies of ibises that had been embalmed by the ancient Egyptians； and showed by comparison that these do not differ in the slightest particular from the ibises that visit the Nile to…day。
Cuvier's reasoning has such great historical interestbeing the argument of the greatest opponent of evolution of that daythat we quote it at some length。
〃The following objections；〃 he says； 〃have already been started against my conclusions。 Why may not the presently existing races of mammiferous land quadrupeds be mere modifications or varieties of those ancient races which we now find in the fossil state； which modifications may have been produced by change of climate and other local circumstances； and since raised to the present excessive difference by the operations of similar causes during a long period of ages？
〃This objection may appear strong to those who believe in the indefinite possibility of change of form in organized bodies； and think that； during a succession of ages and by alterations of habitudes； all the species may change into one another； or one of them give birth to all the rest。 Yet to these persons the following answer may be given from their own system： If the species have changed by degrees； as they assume； we ought to find traces of this gradual modification。 Thus； between the palaeotherium and the species of our own day； we should be able to discover some intermediate forms； and yet no such discovery has ever been made。 Since the bowels of the earth have not preserved monuments of this strange genealogy； we have no right to conclude that the ancient and now
