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 

 characterized by 

 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 

 it approaches in many features the infantile condition, 

 and end in death or extinction. This cycle is repeat- 

 edly 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 



Fig. 32. — Diagram of the relation of repro 

 duction to the Hfe-cycle. 



