BIOLOGY IN HUMAN AFFAIRS 



of the various organ systems, are inherited as we should 

 expect them to be inherited if they are due to one or more 

 genes carried by the chromosomes and distributed by the 

 normal mechanism for such distribution. Sex is even fixed 

 by the possession of a particular type of chromosome carried 

 by all of the eggs but by only one-half of the sperms. And 

 it has been proved that hemophilia (loss of the blood- 

 clotting mechanism) and color-blindness (diminished sensi- 

 tivity of the cones of the eye) are carried in this same 

 chromosome, just as sex-linked characters in other organ- 

 isms are due to genes carried in this so-called X-chromo- 

 some which has the most direct influence over sex. Other 

 more complex characters follow the same scheme. The 

 details of gene interaction are more difficult to determine 

 in such cases, as, for instance, skin color in negro-white 

 crosses; yet it is significant that where complex character 

 differences are under consideration, the genealogical records 

 and the records from the genetics laboratories are virtually 

 identical in character. Mathematical analysis of controlled 

 experiments brings out certain conditions which ought to 

 be satisfied in the genealogical records if the heredity 

 mechanisms are comparable in the two cases; and these 

 conditions are satisfied. Geneticists are convinced, there- 

 fore, that inheritance in man is the same as in melons, or 

 mosquitoes, or monkeys. 



Certain critics who accept this genetic generalization 

 for physical characteristics question whether it holds for 

 mental characteristics. And, unfortunately, the less they 

 have studied the subject, the more positive they are in their 

 assertions. Dr. John B. Watson, the extremist leader, com- 

 pletely oblivious to genetic facts, even boasts that he can 

 make a fool or a genius of any normal child if he begins his 

 instruction at a sufficiently early period. Since man is 

 chiefly interested in man, it may be well to develop the 

 genetic beliefs on this point in a little more detail. The 



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