320 Problems of Organic Adaptation 



the process of chromosome reduction at the time of the 

 formation of the sex cells, each egg receives one x chromo- 

 some, while one half of the spermatozoa receives one x and 

 the other half a y chromosome or none. If then an egg is 

 fertilized by a sperm containing an x, a female is produced, 

 but if fertilized by a sperm containing a y or no sex chromo- 

 some, a male is produced; and since these two types of 

 spermatozoa exist in equal numbers it results by mere chance, 

 on the theory of probabilities, that males and females are 

 produced in equal numbers. But there is no evidence that 

 this remarkable mechanism of sex determination is itself 

 the result of mere chance, and, however it may have been 

 caused, it is a wonderful example of adaptation. 



The fertilization of an egg is a very complex process, and 

 yet every step in that process is adaptive. An egg ready for 

 fertilization gives off substances which activate the sperma- 

 tozoa, and when by its active movements a sperm conies into 

 contact with the egg, the latter sends out a process to re- 

 ceive the sperm. Immediately after this the whole surface of 

 the egg undergoes some change which usually makes it im- 

 possible for another sperm to enter. If by any means more 

 than one sperm nucleus unites with the egg nucleus, the 

 resulting development is very abnormal. Thus the pro- 

 vision for preventing multiple fertilization and pathological 

 development is highly adaptive. Many other cases of intra- 

 cellular adaptations could be cited, but the ones mentioned 

 indicate that adaptations are found in the smallest as well 

 as in the largest parts and functions of organisms "Natura 



7. The Subtle Chemistry of Life 



Although chemists no longer hold that there is a great 

 gulf fixed between organic and inorganic chemistry, and 



