lyo TEANSMJSSIOy OF ACQUIRED CHARACTERS 



Lamarck's Laws. — It may be fairly said that the fons et origo 

 of the afhrmative position was Lamarck. Though he did not 

 originate, he formulated and illustrated the theory of the in- 

 heritance of acquired characters. He maintained the trans- 

 missibility of modifications due to increased and decreased and 

 changed use, and also of modifications due to environmental 

 change, whether directly induced, or indirectly induced by 

 altered function. The giraffe has attained its long neck by 

 stretching it for many generations ; swimming birds have got 

 webbed feet because they stretched their toes in the water ; 

 wading birds have got long legs because they stretched them ; 

 the mole has very small eyes because it has ceased to use them ; 

 the whalebone whale has no functional teeth because it has 

 acquired the habit of swallowing its food without mastication ; 

 and so on. 



Lamarck's two laws of nature, which he said no observer 

 could fail to confirm, were : * 



( 1 ) In every animal that has not passed beyond the term of its 



development, the frequent and sustained use of any organ 

 strengthens it, develops it, increases its size, and gives it 

 strength proportionate to the length of time of its employ- 

 ment. On the other hand, the continued lack of use of 

 the same organ sensibly weakens it ; it deteriorates, and 

 its faculties diminish progressively, until at last it disappears. 



(2) Nature preserves everything that she has caused the individual 



to acquire or to lose by the influence of the circumstances 

 to which the race has been for a long time exposed, and 

 consequently by the influence of the predominant use of 

 certain organs (or in consequence of their continued disuse). 

 She does this by the generation of new individuals, which 

 are produced with the newly acquired organs. This occurs, 

 provided that the acquired changes were common to the two 

 sexes, or to the individuals that produced the new forms. 



Prof. E. Ray Lankester has pointed out (1894) that Lamarck's 



* I have taken the translation from T. H. Morgan's Evolution and 

 Adaptation (1903), p. 226. 



