6 THE PRINCIPLES OF HEREDITY 



descendants of the germ-cell ; that is, they are somatogenetic 

 in origin. They express the modifications of the hereditary 

 characters of the race which are caused in the individual by 

 the play of forces from the environment. 



11. The main mass of inborn or congenital characters are 

 ancient heritages of the race. Thus head, heart, limbs, lungs, 

 liver, the various organs of sense, etc., were possessed by the 

 race of man even before it became human. But, since every 

 individual differs congenitally somewhat from his parents, 

 therefore every individual exhibits some new inborn char- 

 acters. These are usually slight alterations of pre-existing 

 inborn characters an increased or decreased thickness or hair- 

 iness of the skin, a larger nose, a smaller mouth, a stronger 

 heart, a weaker digestion, a broader foot, a narrower hand, a 

 keener sight, a duller hearing, and so forth. Occasionally, 

 however, new inborn characters are of considerable mag- 

 nitude ; or they may not be mere alterations of old characters, 

 but entirely new structures. Such new excessive inborn 

 characters are termed abnormalities. Thus a man may be 

 born very much smaller or bigger, weaker or stronger, than 

 his parents ; or a child of normal parents may be born with a 

 sixth digit on one hand, or deaf, or with a defective heart. 

 All new inborn characters, great or small all new characters 

 which take origin in the germ-plasm, which are congenital, 

 which come to the individual " by nature," which are in- 

 herent in him, which are expressions of his hereditary tend- 

 encies are technically termed "variations." On the other 

 hand, all acquired characters all alterations in an individual 

 caused by the play of external forces on his inborn characters, 

 all such characters as are not congenital in him, such as do not 

 arise in him " by nature," such as do not imply a corresponding 

 and pre-existing trait in the germ-plasm, such as do not 

 express his hereditary tendencies are technically termed 

 " modifications " or " acquirements." 



12. The precise technical meaning of these expressions 

 inborn, congenital, variation, acquirement, modification must 

 be noted. They have not in biological literature the ex- 

 tended and ambiguous significations which they possess in 

 popular literature. At any rate they are intended to have 

 very precise and definite meanings in the present work. 

 Formerly it is true that the term " variation " was used 

 indifferently to indicate all differences, inborn or acquired, 

 between parents and offspring, but of late years most author- 

 ities have agreed to limit the term to inborn differences alone. 

 The word " congenital " is generally used as synonymous 



