The Background of Genetics 3 



substantial forage is provided by the leaves of occasional 

 trees. These animals need to reach up to the leaves, and 

 therefore desire to do so. Through a conscious ejjorl 

 to stretch up to the leaves, their necks and limbs are 

 exercised in such a way as to lengthen them. The small 

 gain in length, possibly only an inch or less, made during 

 the lifetime of the individual is passed on to the progeny, 

 who are successful in adding another inch. The final 

 result is the giraffe. This evolutionary scheme works 

 also in the reverse direction as the result of degeneration 

 through disuse. 



Absurd as some of Lamarck's illustrations may seem, 

 he has really provided the elements of a complete and 

 not unlikely explanation of evolution. The major objec- 

 tion lay in his assumption of the inheritance of acquired 

 characters. Practically all of the earlier expcrmients 

 on this problem seemed to demonstrate that inheritance 

 of acquired characters is impossible, and it was for this 

 reason that the majority of biologists discarded 

 Lamarck's theory. Another objection lay in the fact 

 that conscious effort was hardly to be expected among 

 plants. Lamarck of course recognized this obvious 

 difficulty, and revised his theory in the case of plants, 

 where he claimed the changes were brought about 

 through the direct effects of the environment, citing such 

 things as soil, temperature, moisture, and mechanical 

 pressure. 



The next great explanation was presented in Charles 

 Darwin's Origin of species in 1859. Darwin called 

 attention to the geometric ratio of increase among living 

 organisms, and reiterated the doctrine of ALvlthus to 

 the effect that any population tends to increase more 



