Nos. 622-623] 



ORGANIC EVOLUTION 



gametes certain hypothetical entities to which the name 

 gene or factor has been applied and which give rise to 

 the heritable characters of an organism. Tims it is at 

 once recognized that the problem relates to the origin of 

 the gene, rather than to the origin of the apparent char- 

 acters with which it is correlated, and that by far the 

 greater number of so-called new characters are not new, 

 but were performed at remote periods of time. So far 

 as the present arguments are concerned, it matters not 

 whether the results are assumed to be brought about by 

 material units or enzyme reactions. The prepared poten- 

 tialities exist in either case. 



As examples of extreme types of characters which may 

 arise from the combinations of existing genes and which 

 might have been considered "mutations" at an earlier 

 period when the facts as to their origin were not fully 

 known, one need only mention the ' 'blue" of the Andalu- 

 sian Fowl exhibited by the hybrid between the black and 

 white parental stock, or the "pink" presented by the 

 cross between the red and white "four-o-clocks" of Cor- 

 rens. A type of characters more in line with mutations 

 which have been described and to which there is every 

 reason for believing that many of them may be referred, 

 rests upon multiple gene effects combined with sterility, 

 in accordance with evidence presented by Davis, and oth- 

 ers. Of decided interest in this connection is a recent 

 paper by Muller (1917) calling attention to "An (Eno- 

 thera-like case in Drosophila" where a result quite com- 

 parable to certain mutations of (Enothera is explained 

 through the action of balanced lethal genes. There are 

 other varying degrees of combinations from which "mu- 

 tant" characters may arise and which depend on the be- 

 havior of the genetic material in connection with reces- 

 sives, modifiers, lethals, crossovers, non-disjunction, etc. 



There is really nothing extraordinary in the appear- 

 ance and disappearance of the characters thus formed, 

 beyond their interpretation, and this has furnished false 

 premises for many erroneous conclusions, chief of which, 



