CHAPTER VII. 



HOW CAN GROUPS OF DIFFERENTLY CONSTITUTED 

 TYPES FORM A LINNEON, SIMULATING A SPECIES? 



As we saw in the fifth Chapter, Mendelian behaviour 

 and heredity are different things, consequently here- 

 dity and evolution may very well be quite different 

 problems. 



I would not be at all surprised if definite proof were 

 some day forthcoming that heredity? and evolution are 

 even antagonistic forces. Evolution, as far as at 

 present known facts allow us to judge, is caused 

 by the mating of gametes of different constitu- 

 tions. 



The resulting hybrid gives, after segregation, rise to 

 a certain number of homozygous individuals whose 

 constitution is inherited by their offspring, which then 

 constitute a species, perpetuating its kind faithfully, 

 up to the moment that a new cross intervenes. 



At the moment heredity sets in, evolution therefore 

 stops, and at the moment evolution sets in heredity 

 stops. 



Now in our experiment garden we have it in hand, to 

 let evolution begin and stop at our will : by executing 

 a cross we start evolution, by weeding out the hetero- 

 zygous combinations, obtained by the mating of the 

 differently constituted gametes in F lt and by keeping 

 only the homozygotes and isolating each of these, we 



