120 SYMBIONTICISM AND THE ORIGIN OF SPECIES 



The "presence or absence" hypothesis assumed that dominant 

 characters are due to the presence of a factor and recessive 

 characters to its absence, and since regressive mutations, in 

 which some dominant character becomes recessive, are much more 

 numerous than progressive ones, it was suggested by Shull, 

 Bateson, and Davenport that evolution might be due to the loss 

 or disintegration of factors or genes. "This conception results," 

 said Shull ('07), "in an interesting paradox, namely the produc- 

 tion of a new character by the loss of an old unit," and he sug- 

 gests that at least the later stages of evolution may be a process 

 of analysis due to the disappearance of one unit after another. 

 Bateson ('14) also proposed the same thing in his well-known 

 inquiry "whether the course of evolution can at all reasonably 

 be represented as an unpacking of an original complex, which 

 contained within itself the whole range of diversity which living 

 things present;" and in the same category is the speculation by 

 Davenport that "the foundations of the organic world were laid 

 when a tremendously complex molecule capable of splitting up 

 into a vast number of simpler molecules, was evolved." [Quoted 

 from Conklin.] 



These conceptions, perhaps, have not been generally ac- 

 cepted, although the essential idea of "preformed" or 

 limited genes appears to be retained by most students in 

 genetics. 



It is necessary for us to question the logical probability 

 of one feature of these conceptions of genes. Obviously, 

 it is impossible morphologically to examine a gene, but we 

 are justified in entering into a speculative analysis of these 

 factors, since all the analyses that have gone before have 

 been speculative. This does not necessarily imply that 

 they have been without a basis. But, just as the most 

 generally-accepted view of the nature of mitochondria 

 was based on an assumed or misleading conception of the 

 chemical constitution of these bodies, so also, it appears 

 that an assimied or misleading conception of the nature 

 of genes has led to a "bhnd pocket" in heredity and evolu- 



