150 ILLINOIS STATE ACADEMY OF SCIENCE 



law which says that "all of the acquisitions and losses" 

 are preserved by reproduction on the part of those indi- 

 viduals which have gained by exercise or lost by idleness. 



Lamarck says that this development of powers by 

 exercise occurs in "every animal which has not passed 

 the limit of its development," but he does not state 

 where that limit is. He simply assumes that it continues 

 for some time but furnishes no evidence as to how long 

 that time is. However, I have furnished that evidence in 

 my "Human Heredity," in my article in Volume XITT, 

 page 59, of the Transactions of the Illinois State Acad- 

 emy of Science (1920), and in numerous other contri- 

 butions. Under continuous exercise, powers continue to 

 develop up to practically the end of life ; and under lack 

 of exercise, powers continue to degenerate as long as the 

 lack of exercise continues. While the observed gains and 

 losses are irregular, there is much evidence to indicate 

 that the real gains are directly proportional to the de- 

 gree of activity above the normal, and the length of time 

 that excess activity continues. Also, that the losses are 

 directly proportional to the deficiency of activity and the 

 length of time that deficiency is continued. 



This theory is known as the theory of the inheritance 

 of acquired characters, or, as I usually term it, the in- 

 heritance of acquirements. Power in the organs of an 

 individual is a character which existed before, but the in- 

 crease of the amount of such power is an acquirement. 

 To be technical, ( the verb to acquire means to obtain 

 something by effort, exertion or the performance of work 

 on the part of the individual which makes the acquire- 

 ment. In amputating the tails of mice, the acquirement 

 is in the muscles of the amputator, and not in the tail- 

 lessness of the mice. Taillessness means the loss of some- 

 thing, and the verb to acquire does not mean to lose. 



The American trotter is the product of the nineteenth 

 century and represents what is probably the most re- 

 markable example of the rapid development of powers in 

 any animal. A hundred years ago the highest trotting 

 speed was a mile in three minutes. Now the extreme 



