INTENSIVE SEGREGATION. 327 



Increasing Difference in the Jcinds of Adaptatioiial Selection on 

 !:lie Oontinuance of Regeneration. As was shown in my paper on 

 •'DiTergeut Evolution through CiirauJative Segregation," without 

 the aid of causes preventing intercrossing the selection of other 

 than average forms will produce transformation, but never diver- 

 gence, — will produce Mouotjpie, but never Polytypic Evolution. 



(6) Diversity in the character of the Selection may be intro- 

 duced, not only by the intervention of new forms, but also by 

 the cessation of old forms of Selection. We shall find that 

 important diftereuces of this kind may arise, resulting in con- 

 siderable transformation before any new form of Selection has 

 distinctly supervened. A good illustration of the Gessation of 

 Selection is found in the increasing frequency with which human 

 mothers, notwithstanding their failure to give suck, succeed in 

 raising their children. The power to give suck is through this 

 process being diminished in the more civilized races, though 

 there is no reason to believe that those who do not give suck 

 have, on the whole, any advantage over those who do. The new 

 result is therefore being produced, not by the introduction of a 

 new form of Filio-parental Selectiou, but by the cessation, or the 

 weakening, of an old form. Eomanes was, I believe, the first to 

 point out the eftects that must often be produced by the 

 cessation of Natural Selectiou *, but he has not considered the 

 cessation of other forms of Selection. 



(7) It is often convenient to distinguish between Selection 

 resulting from rational devices and that resulting from the 

 superior success of organisms better adapted than their rivals of 

 the same intergenerant to the natural laws and conditions of the 

 environment, or to the natural constitution of the species to 

 which they belong. The former I call Rational Selection, and 

 the latter Adaptational Selection. Under the former I place 

 Artificial and Institutional Selection, and under the latter I 

 place processes that are as unlike as Natural and Sexual 

 Selection. This classification does not, however, seem to me so 

 important, or so fundamental and clearly definable, as that which 



* See an article on "The Factors of Organic Evolution" in 'Nature, 

 vol. rsxvi. pp. 402-4:04, in which reference is made to previous papers in which 

 the Cessation of Natural Selectiou is discussed. 



LINN. JOUEN. — ZOOLOaX, VOL. XSIII. 22 



