The Source of Variahility 



85 



LUCORA 

 HARPOLA 

 SPATULATA 

 CLARA 



CITROSA 



CORYLORUBRA 



FORNICA 

 OR 



BELLA 



PYRA 



ROSTRATA —ft 



SEPARATA 

 CONTRACTA 

 PHELLOS ( 



VITTATA C 



CARMINl - 



LENTA 



TRIVITTATA " 



IMBRICARIAE - 

 MACULATA — [ 



}basilaris 



-clavipes 

 jturgida 



MIRA 

 EXTERNA 



-MISERA 

 -SPINIGERA 

 -OSBORNI 

 ♦-BALLiSTA 

 HARTI 



Fig. 33. Family tree of the Enjthroneura maculata group of leafhoppers 

 showing the four species thought to be of hybrid origin (each indicated by 

 a large black dot) and the phylogenetic line contributing the smaller number 

 of characters to each (shown by zigzag line). 



polyploidy (Fig. 34) (Babcock, 1957; Anderson, 1949; Lewis and 

 Lewis, 1955). This mixing of characters through hybridization has 

 thus resulted in the origin of many highly successful and novel 

 character combinations and must therefore be considered an im- 

 portant facet of evolution (Stebbins, 1959). 



GENETIC VARIABILITY IN NATURAL POPULATIONS 



Because of the extremely high proportion of lethal, sublethal, and 

 deficiency mutants arising in experimental populations, the idea 

 is frequently expressed that the type of mutation observed in the 

 genetics laboratory does not provide a basis for the kind of char- 



