LECTURE IX 



NATURAL SELECTION, AND THE ANTIQUITY OF LIFE 



IN the "Origin of Species" Darwin says that the sudden appear- 

 ance of species belonging to several of the main divisions of the 

 animal kingdom in the lowest known fossiliferous rocks is at pres- 

 ent inexplicable, and may be truly urged as a valid objection to 

 his views. 



If his theory be true, he says that " it is indisputable that 

 before the lowest Cambrian stratum was deposited long periods 

 elapsed, as long as, or probably far longer than, the whole interval 

 from the Cambrian age to the present day, and that during these 

 vast periods the world swarmed with living creatures. Here," 

 he says, "we encounter a formidable objection; for it seems 

 doubtful whether the earth, in a fit state for the habitation of 

 living creatures, has lasted long enough. To the question why 

 we do not find such fossiliferous deposits belonging to these 

 assumed earliest periods prior to the Cambrian system I can give 

 no satisfactory answer." 



On its geological side this difficulty is even greater than it was 

 in Darwin's day, for we now know that the fauna of the Lower 

 Cambrian was rich and varied ; that most of the modern types of 

 animal life were represented in the oldest fauna which has been 

 discovered, and that all its types have modern representatives. 

 The paleontological side of the subject has been ably summed up 

 by Walcott in an interesting memoir on the oldest fauna which 

 is known to us from fossils, and his collection of one hundred 

 and forty-one American species from the Lower Cambrian is dis- 

 tributed over most of the marine groups of the animal kingdom, 

 and, except for the absence of the remains of vertebrated animals, 

 the whole province of animal life is almost as completely covered 



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