


SUMMARY 
The qualities of an organism result from its development. This deve- 
lopment is caused by the codperation of a great number of factors, 
genetic and non-genetic ones. Whether a gene, present in the inherited 
makeup of an organism will be a factor in its development, depends 
upon whether the developmental stage (or stages) upon which this 
gene must by its very nature act, is (or are) passed through. This , pre- 
sence and absence” theory of the genes makes the assumption of diffe- 
rent states of activity of genes in the germ superfluous. The determi- 
nant conception of heredity should be abandoned. 
Crossing in its widest sense is the chief cause of variability. The rôle 
of mutation, in the sense of spontaneous loss of genes ,in causing varia- 
bility can not be altogether denied, although it is practically impossi- 
ble to prove cases of mutation. 
Wholly new qualities, not only novel combinations of existing cha- 
racters frequently result from novel combinations of existing genes. 
Such novel characters can be shown to be not only anotomical and 
physiological, but also new psychical qualities arise in this way. 
Potential variability is the number of genes in respect to which an 
individual is impure (heterozygous). 
Total potential variability of a group is the sum of the genes in res- 
pect to which not all individuals of this group are equal and pure (ho- 
mozygous). 
A species is a group of organisms, which is so situated and constitu- 
‚ted, that it tends automatically to reduce its Total potential varia- 
bility, and which for this reason tends to become pure for one geno- 
type. 
A variety we call those individuals together, which differ in any 
marked way from the common type of the species they belong to, 
when there is nothing in the circumstances which isolates these orga- 
nisms from crossing freely with the typical ones. 
