The Background of Genetics 9 



Ihem) that take place in li\ijig organisms arc determinate^ 

 taking place along predetermined lines, in a predictable 

 direction, rather than indeterminate, with an equal chance 

 of their taking place in any direction, as the other theories 

 would have it. For example, if a variant is slightly 

 dwarfed as compared with the parent type, there will 

 be among the descendants of this variant a further varia- 

 tion involving greater dwarfedness, and subsequently 

 more changes will take place all involving further steps 

 along this same predetermined line. The direction of 

 the variations is not necessarily related to any environ- 

 mental demand. 



A few authors, regarding orthogenesis as an "explana- 

 tion" of evolution, have visualized an intrinsic ''force" 

 in the organism which guides the variations. Since this 

 view has a vitalistic flavor, it is not popular among scien- 

 tific men. More often it is simply recognized that a 

 certain amount of variation of this sort does take place, 

 and orthogenesis is the name given to the phenomenon, 

 various quite materialistic explanations having been 

 proposed to account for it. 



"Evolution through hybridization" is a theory that 

 was suggested by Weismann some decades ago, and has 

 recently been developed and championed by Lotsy. 

 It is a fact well known among biologists that crossing 

 two distinct types may result, in the second hybrid 

 generation, in a few new and pure-breeding forms, some- 

 what different from anything that had previously 

 existed. Lotsy has shown by experiment that when 

 such new forms (from Antirrhinum crosses) are returned 

 to grow under natural conditions, nature will select 

 some of the types to survive, but will quickly eliminate 



