328 THE SIGNIFICANCE OF SEXUAL REPRODUCTION 



tendency to vary. For the same reason the ova themselves will 

 also cease to vary, and the favourable variation will be transmitted 

 from generation to generation in a stereotyped succession, until 

 unfavourable conditions arise, and again lead to a fresh disposition 

 to vary. 



In this way Brooks ] attempts to mediate between Darwin and 

 Lamarck, for he assumes, on the one hand, that external influences 

 render the body or one of its parts variable, while, on the other 

 hand, the nature of the successful variations is determined by 

 natural selection. There is, however, a difference between the 

 views of Brooks and Darwin, although not a fundamental difference. 

 Darwin also holds that the organism becomes variable by the opera- 

 tion of external influences, and he further assumes that changes 

 acquired in this way can be communicated to the germ and trans- 

 mitted to the offspring. But according to his hypothesis, every 

 part of the organism is continually throwing off gemmules which 

 may be collected in the germ-cells of the animal, while, according 

 to Brooks, this only takes place in those parts which are placed 

 under unfavourable conditions or the function of which is in some 

 way disturbed. In this manner the ingenious author attempts to 

 diminish the incredible number of gemmules which, according to 

 Darwin's theory, must collect in the germ-cells. At the same time 

 he endeavours to show that those parts must always vary which 

 are no longer well adapted to the conditions of life. 



I am afraid, however, that Brooks is confounding two things 

 which are in reality very different, and which ought necessarily 

 to be treated separately if we wish to arrive at correct conclusions : 

 viz., the adaptation of a part of the body to the body itself, and 

 its adaptation to external conditions. The first of these adapta- 

 tions may exist without the second. How can those parts become 

 variable which are badly adapted to the external conditions, but 

 are nevertheless in complete harmony with the other parts of the 

 body ? If the conditions of life, of the cells which constitute the 

 part in question must become unfavourable, in order that the 

 gemmules which produce variation may be thrown off, it is obvious 

 that such a result would not occur in the case mentioned above. 

 Suppose, for example, that the spines of a hedgehog are not suffi- 

 ciently long or sharply pointed to afford protection to the animal, 



1 1. c., p. sj. 



