BINDING ALTERNATIVE PARTICULATE 



320 THE POPULAR SCIENCE MONTHLY 



as for example, in the skin color of mulattoes; such cases were called 

 by Galton " blending" inheritance (Fig. 47). Sometimes characters ap- 

 pear in offspring which were 

 " latent " in the parents but 

 were " patent " in one or more of 

 the grandparents; such skipping 

 of a generation, during which a 

 character remains "latent," has 

 long been known as " atavism." 

 -w ^— At other times characters which 



Fig. 47. Diagram of Galton's were presen . t i n distant ancestors, 

 Law of Ancestral Inheritance. The L 



whole heritage is represented by the en- but which have since dropped Out 



tire rectangle ; that derived from each pro- of gi ~ ht Qr haye rema ined "la- 

 genitor by the smaller squares ; the number ° 



of the latter doubles in each ascending tent," reappear in descendants; 

 generation while its area is halved. After guch cageg are ] mown as « rever . 

 Thompson.) 



sions. 



In still other cases certain characters appear only in the male sex, 

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

 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 permuta- 

 tions in the distribution and combination of ancestral characters new 

 and unexpected characters sometimes develop in the offspring, which 

 were not present, so far as shown, 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 no- 

 ticeable 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 compositions, 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 inclined to assign much importance to 

 them in the general process of evolution. Galton, on the other hand, 

 maintained that variations, 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." 2 



More recently the entire biological world has been greatly influenced 

 by the "mutation theory" of deVries, which has placed a new emphasis 

 upon the importance of sudden variations in the process of evolution. 

 At first deVries was inclined to emphasize the degree of difference be- 



2 "Hereditary Genius," Prefatory Chapter. 



