II.] BELIEF IN ACQUIRED CHARACTERS. 59 



largely by the constitution of the organism, but that va- 

 riation itself, that is, variability, proceeds largely from 

 external causes;, and the characters arising in the life- 

 time of an individual may become hereditar3\ (See 

 page 27.) I must hasten to explain, however, that 

 Darwin clearly recognized the importance of the union 

 of sexes, or crossing, as a cause of variation. 



While Darwin believed that the effects of variability 

 arise ' ' generally from changed conditions acting during 

 successive generations," he nevertheless believed that 

 the first increment of change — that arising in the first 

 individual of a given series — might be directly carried 

 over to the first offspring. That is, he believed in the 

 hereditability of acquired or new external characters, a 

 fact which is emphasized by his conviction that certain 

 mutilations, and even the effects of use and disuse, may 

 be transmitted. Yet, whilst Darwin accepted the doc- 

 trine, he believed it much less thoroughly than Lamarck 

 did, and it is but an incidental part of his philosophy, 

 while it is an essential tenet of Lamarckism. 



Thus far, the hereditability of all important characters 

 had not been disputed. In other words, heredity as a 

 general law or force in the organic world had been 

 assumed. But with the refinement of the discussions it 

 became necessary to conceive of some definite means 

 through which the transmission of particular characters 

 or features should operate; and it was soon found, also, 

 that no philosophy of evolution can expect to explain the 

 phenomena of organic life unless it is connected and co- 

 ordinated with some hypothesis of the method of heredity. 

 While, therefore, a hypothesis of heredity need not 

 necessarily be associated with the abstract theory of evo- 

 lution, all such hypotheses which are now before the 



