iSga.J Elliot, Inheritance of Acquired Characters. QI 



there could be no advancement towards a more perfect develop- 

 ment, and the creature of today would be the same creature it 

 was at its creation, and it would I'emain the same throughout its 

 existence. John T. Gulick* has defined this principle in a 

 manner that seems most satisfactory, and nothing that I have yet 

 seen advanced by the advocates of natural selection as the all- 

 sufficient cause, is able to controvert his conclusions. Mr. Gulick 

 explains: "ist. Unlike to unlike, or the removal of segregating 

 influences, is a principle that results either in extinction through 

 failure to propagate ; or in the breaking down of divergences 

 through free crossings. 3d. Like to like, vv'hen the individuals 

 of each inter-generating group represent the average character ol 

 the group, is a principle through which the stability of existing 

 types is promoted. 3d. Like to like, when the individuals of 

 eivch group represent other than the average character of the 

 group, is a principle through which the transformation of types 

 is eftected." 



In exemplification of these principles this author illustrates 

 them somewhat in this way. Sexual and social instincts often 

 bring in groups like to like together that do not cross, and when 

 the different groups occupy the same area, and are guided by the 

 same habits in the use of the environment, divergences occur even 

 without a diversity of natural selection. He farther explains the 

 way in which this divergence arises. A partial change of plu- 

 mage or development of plumes results from a local segregation ; 

 and through social segregation, the principle that causes animals 

 to associate with those whose appeaiance has become familiar to 

 them, these variations are prevented from being submerged by 

 intercrossing. Then when the invisible instinct and visible char- 

 acter lead individuals thus characterized to associate together, 

 the new characters are intensified, because any individual 

 of the community not imbued with the desire to remain with 

 animals thus changed, will stray from them and fail to breed. 

 He calls this process social selection. Then sexual selection steps 

 in and preserves and accumulates peculiarities of color or plumage, 

 for any individual deficient in these characteristics would be less 

 likely to breed and produce offspring. He concludes as follows : 

 "Varieties thus segregated may often develop divergent habits in 



*;Nature, XLII, 1890, p. 536. 



