June 8, 1900.] 



SCIENCE. 



the offspring of the same parents. It is 

 these differences to which we apply the term 

 variation. The immense importance of the 

 study of variations maj' be judged from the 

 fact that, according to the generally received 

 evolution theory of Darwin, it is to them 

 that the whole of the variety of living and 

 extinct organisms is due. Without varia- 

 tion there could have been no progress, no 

 evolution in the structure of organisms. If 

 offspring had always exactly resembled their 

 parents and presented no points of differ- 

 ence, each succeeding generation would 

 have resembled those previously existing, 

 and no change, whether backwards or for- 

 wards, could have occurred. This phenom- 

 enon of genetic variation forms the bedrock 

 upon which all theories of evolution must 

 rest, and it is only by a study of variations, 

 of their nature and cause, that we can ever 

 hope to obtain any real insight into the ac- 

 tual way in which evolution has taken place. 

 Notwithstaading its importance, the subject 

 is one which has scarcely received from zo- 

 ologists the attention which it merits. 



Though much has been written on the 

 causes of variation, too little attention has 

 of late years been paid to the phenomenon. 

 Since the publication of Darwin's great 

 work on the ' Variation of Animals and 

 Plants under Domestication,' there have 

 been but few books of first-rate importance 

 dealing with the subject. The most impor- 

 tant of these is Mr. William Bateson's work, 

 entitled ' Materials for the Study of Varia- 

 tion.' I have no hesitation in saying that 

 I regard this work as a most important con- 

 tribution to the literature of the Evolution 

 theory. In it attention is called, with that 

 emphasis which the subject demands, to the 

 supreme importance of the actual study of 

 variation to the evolutionist, and a syste- 

 matic attempt is made to classify variations 

 as they occur in Nature. In preparing this 

 book Mr. Bateson has performed a very real 

 service to zoology, not the least part of 



which is that he has made a most effective 

 protest against that looseness of speculative 

 reasoning which, since the publication of 

 the ' Origin of Species,' has marred the 

 pages of so many zoological writers. 



The Variations of Organisms may be 

 grouped under two heads, according to 

 their nature and source: (1 ) There are those 

 variations which appear to have no relation 

 tb the external conditions, for they take 

 place when these remain unchanged, e. g., 

 in members of the same litter ; they are in- 

 herent in the constitution of the individual. 

 These we shall call constitutional varia- 

 tions, or as their appearance seems nearly 

 always to be connected with reproduction, 

 they may be called genetic (congenital, blas- 

 togenic) variations. (2) The second kind 

 of variations are those which are caused 

 by the direct action of external conditions. 

 These variations constitute the so-called oe- 

 quired characters. 



My first object is to consider these two 

 kinds of variations, their nature, their 

 causes and their results on subsequent gen- 

 erations and to inquire whether there are 

 any fundamental differences between them. 

 In this connection it is of particular im- 

 portance that we should inquire whether 

 acquired modifications are transmitted in 

 reproduction. As is well known, there are 

 two schools of thought holding directly op- 

 posite views as to this matter. The one of 

 these schools — the so-called Lamarckian 

 school — holds that they may be transmitted 

 as such in reproduction ; the other school, 

 on the other hand, maintains that acquired 

 modifications affect only the individual 

 concerned, and are not handed on as such 

 in reproduction. That the decision of the 

 matter is not only theoretically important, 

 but also practically, is evident, for upon it 

 depends the answer to the question whether 

 mental or other facilities acquired by the 

 laborious exercise of the individual are ever 

 transmitted to the offspring — whether the 



