Well,I have taken a good deal of pains at various times to prove this,and I have endeavoured to meet the objections of those who maintain,that the structural differences between man and the lower animals are of so vast a character and enormous extent,that even if Mr.Darwin's views are correct,you cannot imagine this particular modification to take place.It is,in fact,easy matter to prove that,so far as structure is concerned,man differs to no greater extent from the animals which are immediately below him than these do from other members of the same order.Upon the other hand,there is no one who estimates more highly than I do the dignity of human nature,and the width of the gulf in intellectual and moral matters,which lies between man and the whole of the lower creation.
But I find this very argument brought forward vehemently by some."You say that man has proceeded from a modification of some lower animal,and you take pains to prove that the structural differences which are said to exist in his brain do not exist at all,and you teach that all functions,intellectual,moral,and others,are the expression or the result,in the long run,of structures,and of the molecular forces which they exert."It is quite true that I do so.
"Well,but,"I am told at once,somewhat triumphantly,"you say in the same breath that there is a great moral and intellectual chasm between man and the lower animals.How is this possible when you declare that moral and intellectual characteristics depend on structure,and yet tell us that there is no such gulf between the structure of man and that of the lower animals?"I think that objection is based upon a misconception of the real relations which exist between structure and function,between mechanism and work.Function is the expression of molecular forces and arrangements no doubt;but,does it follow from this,that variation in function so depends upon variation in structure that the former is always exactly proportioned to the latter?If there is no such relation,if the variation in function which follows on a variation in structure,may be enormously greater than the variation of the structure,then,you see,the objection falls to the ground.
Take a couple of watches--made by the same maker,and as completely alike as possible;set them upon the table,and the function of each--which is its rate of going--will be performed in the same manner,and you shall be able to distinguish no difference between them;but let me take a pair of pincers,and if my hand is steady enough to do it,let me just lightly crush together the bearings of the balance-wheel,or force to a slightly different angle the teeth of the escapement of one of them,and of course you know the immediate result will be that the watch,so treated,from that moment will cease to go.But what proportion is there between the structural alteration and the functional result?Is it not perfectly obvious that the alteration is of the minutest kind,yet that slight as it is,it has produced an infinite difference in the performance of the functions of these two instruments?
Well,now,apply that to the present question.What is it that constitutes and makes man what he is?What is it but his power of language--that language giving him the means of recording his experience--making every generation somewhat wiser than its predecessor,--more in accordance with the established order of the universe?
What is it but this power of speech,of recording experience,which enables men to be men--looking before and after and,in some dim sense,understanding the working of this wondrous universe--and which distinguishes man from the whole of the brute world?I say that this functional difference is vast,unfathomable,and truly infinite in its consequences;and I say at the same time,that it may depend upon structural differences which shall be absolutely inappreciable to us with our present means of investigation.What is this very speech that we are talking about?I am speaking to you at this moment,but if you were to alter,in the minutest degree,the proportion of the nervous forces now active in the two nerves which supply the muscles of my glottis,I should become suddenly dumb.The voice is produced only so long as the vocal chords are parallel;and these are parallel only so long as certain muscles contract with exact equality;and that again depends on the equality of action of those two nerves I spoke of.So that a change of the minutest kind in the structure of one of these nerves,or in the structure of the part in which it originates,or of the supply of blood to that part,or of one of the muscles to which it is distributed,might render all of us dumb.But a race of dumb men,deprived of all communication with those who could speak,would be little indeed removed from the brutes.And the moral and intellectual difference between them and ourselves would be practically infinite,though the naturalist should not be able to find a single shadow of even specific structural difference.
But let me dismiss this question now,and,in conclusion,let me say that you may go away with it as my mature conviction,that Mr.Darwin's work is the greatest contribution which has been made to biological science since the publication of the 'Regne Animal'of Cuvier,and since that of the 'History of Development'of Von Baer.I believe that if you strip it of its theoretical part it still remains one of the greatest encyclopaedias of biological doctrine that any one man ever brought forth;and I believe that,if you take it as the embodiment of an hypothesis,it is destined to be the guide of biological and psychological speculation for the next three or four generations.
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