ACQUIRED CHARACTERS li 



of soma that grows upon it : its soma-growing potentialities 

 have radically altered. These potentialities have been 

 acquired and modified by intercourse with the environment 

 through many million years : using the term environment 

 in the widest possible sense to denote any kind of physico- 

 chemical cause that produces variation in the germ-cell. 

 If now some modification is impressed upon the soma of 

 any individual, and if that modification does really induce 

 a corresponding alteration of the germ-plasm, it would appear 

 that such alteration could only be of infinitesimal extent, 

 since it is brought into contact with a germ-plasm whose 

 constitution has been moulded into its present form by 

 factors which have worked for many million years. An 

 analogy wiU make my meaning clear. 



Suppose that a bullet was fired from one of the nearest 

 fi:xed stars such as a. Centauri directly at the centre of London, 

 and suppose that it travelled the entire distance in a straight 

 line. Now, when it is starting its journey, suppose that 

 a new environmental force operates in such a way as sUghtly 

 to deflect the bullet from its course. Suppose that this 

 variation is so excessively small that after traveUing on- 

 wards for a further quarter of a million miles, it is still only 

 one inch out of its original course. Yet the total journey 

 before it is so inconceivably great, that it is easy to calculate 

 that this minute deflection may cause the bullet, not only 

 to fail striking London, but to miss the Earth altogether. 



Now we may compare the career of this bullet through 

 space with the career of the germ-plasm through time. We 

 may compare the successive miles accomplished by the 

 bullet with the successive generations of its parasitic somata. 

 We may compare the force which deflects it from its course 

 with the factor that causes a variation in the germ-plasm. 

 And the application is at once obvious. Environmental 

 factors which have been in operation milHons of generations 

 have caused in the germ-cell a great and permanent varia- 

 tion : environmental factors which have only just come into 

 operation will influence the germ-ceU to an infinitely minute 



