按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
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 extinct species were as permanent in their forms and characters as those which exist at present； or； at least； that the catastrophe which destroyed them did not leave sufficient time for the productions of the changes that are alleged to have taken place。
〃In order to reply to those naturalists who acknowledge that the varieties of animals are restrained by nature within certain limits； it would be necessary to examine how far these limits extend。 This is a very curious inquiry； and in itself exceedingly interesting under a variety of relations； but has been hitherto very little attended to。 。 。 。 。 。 。 。 。
Wild animals which subsist upon herbage feel the influence of climate a little more extensively； because there is added to it the influence of food； both in regard to its abundance and its quality。 Thus the elephants of one forest are larger than those of another； their tusks also grow somewhat longer in places where their food may happen to be more favorable for the production of the substance of ivory。 The same may take place in regard to the horns of stags and reindeer。 But let us examine two elephants； the most dissimilar that can be conceived； we shall not discover the smallest difference in the number and articulations of the bones； the structure of the teeth； etc。 。 。 。 。 。 。 。 。
〃Nature appears also to have guarded against the alterations of species which might proceed from mixture of breeds by influencing the various species of animals with mutual aversion from one another。 Hence all the cunning and all the force that man is able to exert is necessary to accomplish such unions； even between species that have the nearest resemblances。 And when the mule breeds that are thus produced by these forced conjunctions happen to be fruitful； which is seldom the case； this fecundity never continues beyond a few generations； and would not probably proceed so far without a continuance of the same cares which excited it at first。 Thus we never see in a wild state intermediate productions between the hare and the rabbit； between the stag and the doe； or between the marten and the weasel。 But the power of man changes this established order； and continues to produce all these intermixtures of which the various species are susceptible； but which they would never produce if left to themselves。
〃The degrees of these variations are proportional to the intensity of the causes that produced themnamely； the slavery or subjection under which those animals are to man。 They do not proceed far in half…domesticated species。 In the cat； for example； a softer or harsher fur； more brilliant or more varied colors； greater or less sizethese form the whole extent of variety in the species； the skeleton of the cat of Angora differs in no regular and constant circumstances from the wild…cat of Europe。 。 。 。 。 。 。 。
The most remarkable effects of the influence of man are produced upon that animal which he has reduced most completely under subjection。 Dogs have been transported by mankind into every part of the world and have