70 



GENETICS 



ably of an intrinsic or germinal nature. Evening 

 primroses display the same mutants whether in 

 Holland or America, in a wild state or under culti- 

 vation. Mutations, like poets, are born, not made. 

 It has been suggested by Standfuss that species 

 may go through the same kind of a life-cycle that in- 

 dividuals do, only 

 taking infinitely 

 more time to do 

 it. As shown in 

 Figure 32, they 

 are born of other 

 species and enter 

 the prodigious 

 growth period of 

 infancy and youth, 

 both of which are 



PIG. 32. Diagram of the relation of repro- characterized by 

 duction to the life-cycle. in A 



much fluctuation. 



With maturity they gradually become comparatively 

 stable until the reproductive period is reached, when 

 they throw off their progeny, as on a tangent. They 

 finally pass into the excessively differentiated period 

 of old age, from which there is no recall, although 

 they approach in many features the infantile condi- 

 tion, and end in death or extinction. This cycle is 

 repeatedly illustrated by phylogenetic lines of fossil 

 forms which have long since become extinct. 



Beecher has pointed out ^.that, in paleontological 

 times just before they became extinct, species often 

 underwent extreme specialization in the form of 



