Il8 DARWINISM AND THE PROBLEMS OF LIFE 



species. Formerly the common element that made it 

 possible to distribute organisms into species, orders, 

 etc., was taken for granted without discrimination. 

 Darwin, and a few students before his time, have tried 

 to show why there are common features amongst living 

 things. 



There are two laws that explain these common 

 elements in the animal world. One is the law of 

 adaptation; and we shall see later that adaptation to 

 precisely the same conditions can bring such very 

 different animals as worms and spiders to resemble each 

 other. The second is the law of heredity. According 

 to this law organisms have more in common, the closer 

 their blood-relationship is. Any person can verify this 

 from human life. However, it is not as simple as it 

 seems at first sight, and we shall see, when we deal with 

 the phenomena of heredity, that frequently men who are 

 only distantly related resemble each other more than 

 brothers and sisters. 



The law of heredity gives a general validity to the 

 classification of the animal kingdom, as it was set up 

 formerly on the ground of common features ; we have 

 much the same arrangement when we classify them 

 according to generic relationship. There are, however, 

 many exceptions, and these are explained by the first 

 law. Animals were formerly classed together which 

 resembled each other externally through some similar 

 adaptation. But the more thoroughly they were 

 investigated, the more they were found to have in 

 common with different animals, and they are now 

 distributed in other orders and classes. This common 



