74 Heredity and Environment 



such skipping of a generation, during which a character re- 

 mains "latent," has long been known as "atavism." At other 

 times characters which were present in distant ancestors, but 

 which have since dropped out of sight or have remained "latent," 

 reappear in descendants ; such cases are known as "reversions." 



In still other cases certain characters appear only in the male 

 sex, others only in the female, this being called "sex-limited" in- 

 heritance ; while in some instances characters are transmitted from 

 fathers through daughters to grandsons or from mothers to sons, 

 all such cases being known as "sex-linked" inheritance.* 



2. New Characters or Mutations. But in addition to these 

 permutations in the distribution and combination of ancestral 

 characters new and unexpected characters sometimes develop 

 in the offspring, which were not present, so far as known, in any 

 of the ascendants, but which, after they have once appeared, are 

 passed on by heredity to descendants. Such inherited variations 

 are usually of two kinds, continuous or slight, and discontinuous 

 or "sudden" variations. The latter are especially noticeable when 

 variations occur in the normal number of parts, as in four-leaved 

 clover, or six-fingered men, and such numerical variations have 

 been called by Bateson "meristic." However, sudden variations 

 may include any marked departure from the normal type, in color, 

 shape, size, chemical composition, etc. Such sudden variations 

 have long been known to breeders as "sports," and both Darwin 

 and Galton pointed out the fact that such sports have sometimes 

 given rise to new races or breeds, though Darwin was not in- 

 clined to assign much importance to them in the general process 

 of evolution. Galton, on the other hand, maintained that varia- 

 tions, or what would now be called "continuous variations," can- 

 not be of much significance in the process of evolution, but that 

 the case is quite different with "sports" ("Hereditary Genius," 

 prefatory chapter). 



More recently the entire biological world has been greatly influ- 



*See p. 187. 



