THEORIES OF HEREDITY AND VARIATION. 55 



number of generations, that external circumstances are without 

 influence that will reach a succeeding generation. A man may be 

 born weak and frail, yet may, by care with his food and bodily 

 exercise, develop into a robust individual, but the Weismannians 

 insist that that fact will not make his children stronger or healthier, 

 because they claim it is the somatic cells and not the germ cells that 

 are developed and strengthened. To admit such a result would be 

 to admit use-inheritance, the denial of which is a fundamental part 

 of their theory. 



NEO-DARWINIANS AND NEO-LAMARCKIANS. 



Those who support the Weismannian theory, and other theories 

 of a similar character, call themselves Neo-Darwinians, not because 

 Darwin was a believer in any such doctrine, but because they explain 

 evolution entirely by variation and selection, the elements on which 

 Darwin based his theory of the Origin of Species. In this, however, 

 they go much beyond Darwin by making "variation" into "con- 

 genital variation," while Darwin believed that variations were due 

 in part to the accumulated effects of use and disuse. While the Neo- 

 Lamarckians explain the loss of the power of flight in domestic ducks 

 to the disuse of their wings, the Neo-Darwinians explain that tame 

 ducks, not being required to fly to procure food and to escape ene- 

 mies, the variations toward greater wing power are not preserved by 

 selection, and consequently that wing power deteriorates. They also 

 argue that ducks with greater wing power are more liable to escape, 

 and that man deliberately kills off ducks liable to escape by flying, 

 and preserves those less able to fly and less wild. They thus bring 

 selection to explain what had before been explained by the inherited 

 effects of use and disuse. 



It is maintained by the Neo-Darwinians that as long as any 



