FROM THALES TO LAMARCK 11 



Which forces have been responsible for this development ? To 

 this Lamarck replies, that ' it is the change of function of the 

 individual organs which brings about this seeming miracle.' 



We may at any time observe in our own body the effects of 

 the use or disuse of an organ. Systematic exercise produces 

 better and stronger muscles ; the fibres not only increase in 

 volume, but are also able to act and contract more quickly. Con- 

 versely, want of action produces slackness and degeneration of 

 the fibres. A person whom illness or accident keeps to the bed 

 and from all action knows that after a few weeks the legs will 

 be so weakened as scarcely to be able to support the weight of 

 the body. Like a child, the patient must perforce once more 

 strengthen the muscles by gradual exercises, that is, he must 

 again learn to walk. Supposing that it were possible to transmit 

 to the next generation the primary constituents (Anlagen) of such 

 characters newly acquired by exercise (in this case the invigora- 

 tion or degeneration of the muscle fibres) and that this and 

 following generations would act similarly, organisms might 

 eventually be found which would be widely differentiated from 

 their original parents ; for it is obvious that a radical modifica- 

 tion of the muscles would in one way or another influence also 

 the development of the other parts of the body. 



Who does not know Lamarck's instance of the giraffe? In 

 earlier times giraffes were probably, like other ruminants, of normal 

 build, nor differing greatly in the neck from their congeners. 

 The severe competition arising on the ordinary grazing grounds 

 from the presence of other herbivorous animals forced the 

 giraffes to profit by their comparative height and seek nourish- 

 ment on the branches of trees. The continual stretching and 

 exercising of the neck caused a richer circulation, a better 

 feeding of the muscles and other tissues, and a slight addition 

 to its length which was transmitted to the offspring. Continued 

 in subsequent generations, this process gradually produced in the 

 course of many thousands of years an abnormally long neck such 

 as we see to-day. The web between the toes of the waterfowl 

 is said to have been caused through the habit of these birds of 

 seeking their prey on the water and of spreading out their toes 

 as widely as possible in order to swim better. The continued 

 stimulus acting upon the skin between the toes gradually effected 



