Many Sources of Error 17 



conditions, and on the other hand as showing the selective 

 action of the environment in bringing about adaptation; 

 and still other interpretations may prove to be sounder. The 

 remarkable resemblances in general appearance sometimes 

 found between insects of different families, even of different 

 orders, is an impressive fact which undoubtedly has some 

 bearing on the question of evolution, but the analysis of this 

 fact into its fundamental physiological sources has discredited 

 the doctrine of ** mimicry " as a support of the general doc- 

 trine of organic evolution. 



Many Sources of Error 



In the study of fossils it has been necessary to guard 

 against casual lumps of stone or clay that resemble superfi- 

 cially some structure produced by an animal. Nobody today 

 believes that fossils represent mere freaks of nature, or 

 the playful production of mineral imitations of organic 

 structures by a creative intelligence, yet there have been 

 found clods of earth that were only clods of earth, in 

 spite of such resemblances. 'WTien the explorers of the 

 Gobi Desert brought back petrified Dinosaur eggs, it was 

 proper not only for skeptics but for sympathetic scientists 

 to ask, " How do you know they are eggs and not rounded 

 stones? " 



The historian must be on his guard against falsifications 

 of the records bv accidental or bv intentional dislocations. 

 The finding in an emperor's tomb of a sword showing work- 

 manship and ornamentation characteristic of a foreign people 

 is a significant fact for the historian; but he does not have 

 to elaborate it into showing the versatility of the emperor or 

 of his artisans. In the same way the student of evolution 

 must guard against drawing faulty conclusions from dislo- 

 cated materials. Holes dug for water or for minerals or even 

 for scientific purposes have displaced the original inclusions 

 and so have misled later students. Materials transported by 

 man or washed out of place by inundations have complicated 



