SOCIAL EVOLUTION 



VARIATION AND HEREDITY 



It is a fact of general observation that the offspring of 

 plants and animals tend to resemble the particular in- 

 dividuals from which they have sprung. ''The young of 

 a horse is always a horse and never a zebra. Wolves do 

 not give birth to foxes. Sunflowers will not grow from 

 thistle seed." ^ Nature keeps things in order, or, as the 

 biologist says, plants and animals breed true. We have 

 come to regard this relation as an established principle. 

 But in Ancient and Medieval times many people believed 

 that certain plants transformed into animals. In the 

 ]\Iiddle Ages they thought that tlie liarnacle-goose orig- 

 inated from the goose-barnacle.^" Since then, our knowl- 

 edge of natural law has so greatly increased that we are 

 able to assert witli utmost confidence that plants and 

 animals breed true. 



Tliis likeness of parent and ol^'spring is of such a na- 

 ture that the young usually bear a somewhat close re- 

 semblance to their i)arents, in addition to sliaring the 

 wider similarity of structure and function which makes 

 them belong to ilie same species as tlieir parents. Tims 

 the resemblance is both detailed and general. The off- 

 spring of domestic cattle are like their parents in such 

 characteristics as size, form, color, and amount of milk."' 



iMetoalf. M. M.—Orfiavir Emhition. .'ird cd.. 1011. p. 3. 

 i-a Ibiil. 1-1) Iliid., p. (1. 



