228 



NATURE 



\7an 3, i: 



The doctrine of evolution, as taught by the biologists of to- 

 day, has several stages as grounds or parts of its presentation. 

 First, the foundation principle is this : That the species of ani- 

 mals and of plants, the species of organic beings, as well as the 

 various natural division^ into which th;se organic being; fall, 

 have not always been as we see them to-day, but they have been 

 produced by a process of change which has progressed from age 

 to age through the influence of natural laws ; that, therefore, 

 the species which now exist are the descendants of other species 

 which have existed heretofore, by the ordinary processes of re- 

 production ; and that all the various structures of organic beings 

 which make them what they are, and which compel them to act 

 as they now act, are the result of gradual or sudden modifica- 

 tions and changes during the periods of geologic time. That 

 is the first phase or aspect which meets the naturalist or 

 biol igist. 



All ither phase of the question relates to the origin itself of 

 that life which is supposed to inhabit or possess organic beings. 

 There is an hypothesi. of evolution which derives this life from 

 no-life, which derives vitality from non-vitality. That is another 

 branch of the subject, to which I cannot devote much attention 

 to-day. There is still another department of the subject, which 

 relates to the origin of mind, and which derives the mental 

 organisation of ihe higher animals, especially of man, from pre- 

 existent types of mental organisation. This gives us a genealogy 

 of mind, a history of the production or creation of mind, as it is 

 now presented in its more complex aspects as a function of the 

 human brain. This aspect of the subject is, of course, interest- 

 ing, and upon that I can touch with more confidence than upon 

 the question of the origin of life. 



Coming now to the question of the origin of structures, we 

 have by this time accumulated a vast number of facts which 

 have been collated by laborious and faithful workers, in many 

 countries and during many years ; so that we can speak with a 

 good deal of confidence on this subject also. As to the pheno- 

 mena which meet the student of zoology and botany at every 

 turn, I would merely repeat what every one knows — and I beg 

 pardon of my biological friends for telling them a few well- 

 known truth--, for there may be those present who are not in the 

 Biolo Tical Section— th it the phenomena w hich meet the student of 

 biology come under two leading classes : iheone is the remarkable 

 fidelity of species in reproducing their like. "Like produces 

 like," is the old theorem, and is true in a great many cases ; just 

 as coins are struck from the die, just as castings are turned out 

 from a common mould. It is one of the most wonderful pheno- 

 mena of nature, thit such complex organisms, consisting of so 

 many parts, should be repeated from age to age, and from gene- 

 ration to generation, with such surprising fidelity and precision. 

 This fact is the first that strikes the student of these sciences. 

 The general impression of the ordinary person wou'd be that 

 these things must continue unchanged. When I began to study 

 zoology and botany, I was remarkably surprised to find there 

 was a science of which I had no conception, and that was this 

 remarkable reproduction of types one after another in succession. 

 After a man has had this idea thoroughly assimilated by his honest 

 and conscientious studies, he will be again struck with another class 

 of facts. He will find, not unfrequently, that this doctrine does 

 not apply. He will find a series of facts which show that many 

 i'ldividuals fail to coincide with their fellows precisely, the most 

 remarkable variations and the most remarkable haif-w-ay atti- 

 tudes and double sided aspects occurring ; and he will come to 

 thecmclu Idu, sooner or later, that like does not produce like 

 with the same precision and fidelity with w hich he had sui>po<ed 

 it dil. So that we have these two classes of facts, — the one 

 relating t >, and expressing, the law of heredity ; the other, which 

 expresses the law of metamorphosis. I should not like to say 

 which class of facts is the most numerously presented to the 

 student. In the present fauna we find many groups of species 

 and varieties before us ; but how many species we have, how 

 many genera we have, and families, we cannot definitely sl.ate. 

 Th; more precise and exact a person is in his definition and in 

 his analysis, the more definite his science becomes, and theinore 

 precise and scientific his work. It is a case of analy^is and 

 forms. What the scales are to the chemist and the physicist, 

 the rule and measure are to the biologist. It is a question of 

 dimensiMi, it is a question of length and bre.adth and thickness, 

 a question of curves, a question of crooked shapes or simple 

 shape;, — rarely simple shapes, mostly crooked, generally bi- 

 lateral. It require! that one should have a mechanical eye, and 

 should have also tonething of an artistic eye to appreciate these 



forms, lo measure them, a id to be able to compare and weigh 

 them. 



Now, when we come to arrange our shapes and our measure- 

 ments, we find, as I said before, a certain number of identities, 

 and a certain number of variations. This question of variation 

 is so common and so remarkabl", that it liecomes perfectly 

 evident to the specialist in each department that like doe> not 

 at all times produce like. It is perfectly clear, a'ld I will 

 venture the assertion that nearly all the biologists in this room 

 will bear me witness, that variability is practically unlimited in 

 its range, unlimited in the number of its examples, unlimited in 

 t'le degree to which it extends. That is to .say, the species vary 

 by failing to retain certain characteristics, and generic and other 

 characters are found to be absent or present in accordance with 

 some law to be discussed further on. 



1 believe that this is the simplest mode of stating and explain- 

 ing the law of variation : that some forms acquire something 

 which their parents do not posess ; and that those which acquire 

 something additional have to pass through more numerous stages 

 than those which have not acquired so much had themselves 

 passed through. 



Of course we are met with the opposite side of the case, — this 

 law of heredity. We are told that the facts there are not ac- 

 counted for in that way ; that we cannot pass from one class of 

 facts to the other class of facts ; what we find in one class is 

 not applicable to the other. Here is a question of rational pro- 

 cesses, of ordinary rea'ion. If the rules of chemistry are true 

 in America, I imagine they are true in Australia and Africa, 

 although I have not been there to see. If the law of gravitation 

 is effective here, I do not need to go to Australia or New Zea- 

 land lonscertain whether it is true there. So, if we find in a 

 group of animals a law sufficient to account for their creation, 

 it is not neces.sary to know that others of their relatives have 

 gone through a similar process. I am willing to allow the 

 ordinary practical law of induction, the practical law of infer- 

 ence, to carry me over these gaps, over these interruptions. 

 And I state the case in that way, because this is just where some 

 people differ from me, and that is just where I say the simple 

 question of rationaliiy comes in. I cannot believe that nature's 

 la\\s are so dissimilar, so irregular, so inexact, that those which 

 w e can see and understand in one place are not true in another ; 

 snd that the question of geological likelihood is similar to the 

 question of geographical likelihood. If a given process is true 

 in one of the geological periods it is true in another ; if it is true 

 in one part of the world it is true in another ; because I find 

 interruptions in the series here, it does not follow that there need 

 be interruptions clear through from age to age. The assumption 

 is on the side of that man who asserts that transitions have not 

 taken place between forms which are now distinct. 



We are told that we find no sort of evidence of that transition 

 in past geological periods ; we are assured that svc'i changes 

 have not taken place ; we are even assured that no such sign of 

 such transition from one species to another has ever been ob- 

 served, — a most as'.onishing assertion to make to a biologist, or 

 by a biologist ; and such persons have even the temerity to cite 

 special cases, as between the wolf aiid the dog. Many of our 

 domestic do^s are nothing but wolves, which have been modified 

 by the hand of man to a very slight extent indeed. Many dogs, 

 in fact neaily all dogs, are descendants of w'ild species of various 

 countries, and are but slightly modified. 



To take the question of the definition of species. Supposing 

 we have several species well defined, say four or five. In the 

 process of investigation we obtain a larger number of individual , 

 many of w hich betray characters which invalidate the definitions. 

 It becomes necessary to unite the four or five species into one. 

 And so then, because our system requires that we shall have 

 accurate definitions (the whole basis of the system is definitions — 

 you know the very comprehension of the subject requires defini- 

 tions), we throw them all together, because we cannot define all 

 the various special forms as we did before, until we have but one 

 species. And ihe critic of the view of evolution tells us, "I 

 told you so ! There is but one species, after all. There is no 

 such thing as connection between species; you never will find 

 it." Now, how many discoveries of this kind will be necessary 

 to convince the world that there are coi.nections between 

 species ? How long are we to go on finding connecting links, 

 and putting them together, as we have to do for the sake of the 

 definition, and then be told that we have nevertheless no inter- 

 mediate forn.s between species? The matter is too plain for 

 further comoient. We throw them together simply because our 



