202 CAUSES OF VARIATION 



Weismann x believes that in nature the death point has been 

 fixed at an age most profitable to the race as a whole. That is 

 to say, it is best for the race (i) that only the strongest should 

 survive to the breeding age ; (2) that these should live as long 

 as they are able to reproduce; and that (3) they should then die 

 and cease to occupy room and consume food which would other- 

 wise be available for the sustenance of more robust individuals 

 engaged in reproduction. This fixes the death point theoretic- 

 ally at the cessation of reproduction, except in such species as 

 those in which the young need the care or the educative assist- 

 ance of the mother. In these the theoretical death point would be 

 at the maturity of the last young. This of course is in reference 

 to wild species, and Weismann believes that nature has estab- 

 lished the death point in close correspondence to this principle. 



However that may be, there is a problem here for the breeder. 

 It is for him to fix the death limit well beyond the period of the 

 particular service required. In nature there is but one object in 

 life, self-preservation and reproduction. On our farms there 

 are other objects. The horse is for labor, and his serviceable 

 age as well as his degree of intelligence needs to be lengthened 

 as much as possible. In nature early and rapid reproduction is 

 a full equivalent for longevity. It is not so on our farms, where 

 the individual counts for more, and even rapid reproduction 

 cannot take the place of long life and faithful service. 



SECTION XIV BATHMIC INFLUENCES 



Do species possess inherent tendencies to vary ? If a race 

 could be surrounded by positively unchanging conditions, if it 

 could produce asexually, and if all types were equally vigorous 

 and equally fertile, would it remain constant? Some variation 

 would arise through reduction, but this would be heterogeneous, 

 that is, now in one direction, now in another. The real ques- 

 tions the bathmic evolutionist asks are these : Is there a tend- 

 ency for the type to drift, independent of selection or surrounding 

 influences ? Are its deviations characterized by a continual bias 



1 Weismann, Essays on Heredity, T, 111-163; see also Pearson, Chances of 

 Death, pp. 1-42. 



