AforsT :!l, 188:;.] 



SCIENCE. 



v.] 



The doctrine of evolution, as taught by the biolo- 

 pisls of to-il:iy, ha-i sevoral stages as grounds or parts 

 of its presiMiliition. First, the foundation principle 

 istlii<: Thai the species of animals and of plants, 

 the species of organic beings, as well as the various 

 natui-al divisions into which these organic beings 

 fall, have not always been sls we see them to-day, 

 but they have been produced by a process of change 

 ■wliii'h has progres^sed from age to age through the 

 indniMice of natural laws; that, therefore, the spe- 

 oie< which now exist are the descendants of other 

 species which have existed heretofore, by the ordinary 

 processes of reproduction; and that all the various 

 structures of organic heing-s, which make them what 

 they are, and which compel them to act as they now 

 act, are the result of gradual or sudden modifications 

 and changes during the periods of geologic time. 

 Tliat is the first phase or aspect which meets the 

 inituralist or biologist. 



.Vnolher phase of the question relates to the origin 

 itself of that life which is supposed to inhabit or 

 possess org.anic beings. There is an hypothesis 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 organization of the 

 biglier animals, especially of man, from pre-existent 

 types of mental organization. This gives us a gene- 

 alogy 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, interesting; and 

 upon that I can touch with more confidence than 

 upon the question of the origin of life. 



Coming now to the <iuestion of the origin of 

 structures, we have by this time accumulated a vast 

 number of facts which have been collated by labo- 

 rious and faithful worl<ers, 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 phenomena which meet the student of zoology 

 and botany at every turn, I would merely repeat, what 

 every one knows, — and 1 beg pardon of my biological 

 friends for telling them a few well-known truths, f„r 

 there may be those present who are not in the biolo- 

 gical section, — the phenomena which meet the stu- 

 dent of biology come under two leading classes: the 

 one is the remarkable fidelity of species in reprodu- 

 cing their like. ' Like produces like,' is the old theo- 

 rem, and is true in a great many cases; just as C(rins 

 are struck from the die, just as castings are turned 

 out from a common moulil. It is one of the most 

 wonderful phenomena of nature, that such complex 

 organisms, consisting of so many parts, should be 

 repeated from age to age, and from generation to 

 generation, with such surprising fidelity and pre- 

 cision. This fact is the first that strikes the student 

 of these sciences. The general impression of the 

 ordinary person would be, that these things must con- 

 tinue unchanged. When I began to study zoology 

 and botany, I was remarkably surprised to find there 



was a science of which I had no concejilion, and 

 that was this remarkable reproduction of types one 

 after another in succession. After a man has had 

 this idea tlioroughly assimiLatcd by his honest and 

 conscientious studies, he will be .again struck with an- 

 other class of facts, lie will find, not unfrequenlly, 

 that thisdoetrinedoes not apply. He will find a. series 

 of facts which show that many individuals fail to coin- 

 cide with their fellows precisely, the most remarkable 

 variations and the most remarkable half-way attitudes 

 and double-sided aspects occurring; and he will come 

 to the conclusion, s inner or laic-r, that like dues 

 not jjroduce like with the same precision and fidelity 

 with which he had supposed it did. So that we have 

 these two cla.sses of facts, — the one relating to, and 

 expressing, the law of heredity; the other, which 

 expresses the law of metamorphosis. I sh'>nlil not 

 like to say which chass of facts is the most numer- 

 ously 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 state. The 

 more precise and exact a person is in his definition 

 and in his analysis, the more definite his science be- 

 comes, and the more precise and scientific his work. 

 It is a case of analysis and forms. What the scales are 

 to the chemist and the physicist, the rule and meas- 

 ure are to the biologist. It is a question of dimension, 

 it is a question of length and breadth and thickness, 

 a question of curves, a question of crooked shapes or 

 simple shapes. — rarely simple sh.apes, mostly crooked, 

 generally bilateral. It requires that one should have 

 a mechanical eye, and should have also something of 

 an artistic eye, to appreciate these forms, to measure 

 them, and to be able to compare and weigh them. 



Now, when we come to arrange our shapes and our 

 measurements, we tiiul, as I said before, a certain 

 number of identities, and a certain number of varia- 

 tions. This question of variation is so common and 

 so remarkable, that it becomes perfectly evident to 

 the specialist in each department, that like does not 

 at all limes produce like. It is perfectly clear, and 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 the degree to 

 which itextends. 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 farther 

 on. 



I believe that this is the simplest mode of stating 

 and explainins the law of variation: that some forms 

 ac<|uire something which their parents do not pos- 

 sess; and that those which ac<|uire something addi- 

 tional have to pass through more numerous stages 

 than those which have not acquired so much bad 

 themselves passed through. 



Of course we ai'j; met with the opposite side of the 

 case, — this law of heredity. We are told that the 

 facts there are not accounted 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 



