Chapter III 

 Our Surroundings 



WE have seen that if animals showing good points 

 are selected for breeding purposes, generation after 

 generation, the result will be an improvement in the breed. 

 This is because any good point noted in a parent as a rule 

 will reappear to some extent amongst its descendants; 

 or, in other words, it will generally be inherited. We have 

 thus far accepted this as a fact merely because it is a matter 

 of common knowledge. Doubts and difficulties are, how- 

 ever, constantly being raised when it is proposed to apply 

 this knowledge in human affairs. Something must, there- 

 fore, be said to make this certainty doubly certain. 



As we have seen, every human being is developed out 

 of a minute germ. These germs are at first quite indis- 

 tinguishable from each other in appearance. Nevertheless, 

 putting aside the case of twins, who resemble each other 

 closely, now often called identical twins, nO two germs are 

 ever exactly like each other. And the differences between 

 the germs are such as to give rise to differences between 

 the individuals developing from them. Since no two germs 

 are alike, no two human beings are alike either. And the 

 differences between men, which result from differences 

 between the germs from which they originated, are known 

 as hereditary differences. If one man has blue eyes and 

 another brown, this is as good an example as can be given 

 of an hereditary difference. 



These are, however, not the only kind of differences 

 which exist between human beings. Men meet with 

 different surroundings as they are developing from their 

 originating germs and, indeed, during all their lives. The 

 surroundings to which men are exposed may leave an 

 indelible mark on them, and may thus make them differ 



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