OTHER THEORIES OF SPECIES-FORMING. 271 



cells, etc. Use and disuse are equivalent simply to much or 

 little metabolism, and metabolism is as necessary to produce 

 passive organs or to change them, as use is to make muscles 

 larger. 



However, despite the successful destructive criticism by 

 Weismann and the neo-Darwinians of the alleged cases of 

 Many natural- tne inheritance of acquired characters adduced 

 ists believe in by the Lamarckians, and in spite of our lack of 

 of acquired knowledge, and indeed, difficulty of conception 

 characters, o f anv mechanism in the body capable of im- 

 pressing on the germ-plasm the effects of use, disuse, and 

 external stimuli in such a way as to compel a photographic 

 reproduction in the young of these effects as manifest in 

 the soma of the parent, numerous biologists do not hesitate 

 to avow their conviction of the actuality of such inheritance. 

 Now these biologists must have some basis of observation or 

 scientific fact for their belief. What is this basis ? They rest 

 their belief largely upon a kind of proof by indirection, a 

 certain necessity of consequence of other facts, and a logical 

 argument by elimination. The actual observed status of 

 animal life to-day and, as revealed by fossils, in past ages, 

 which is that of the existence of certain lines of descent or 

 evolution obviously following lines of modification based 

 on use and disuse; the inadequacy of natural selection to 

 explain the cumulation of adaptive modification until such 

 modification shall have reached a life-and-death determin- 

 ing selective value ; the apparent impossibility of explaining 

 the continued degeneration of vestigial organs by natural 

 selection ; the great difficulty of explaining correlative or 

 coadaptive modifications by selection alone; the possibility 

 that our lack of knowledge of a mechanism for ensuring the 

 hereditary transmission of acquired characters may be over- 

 come with further knowledge of the ultimate structure and 

 capacity of the germ-plasm; the great reasonableness and 

 logical plausibility of the whole Lamarckian conception; 



