8 THE CASE AGAINST EVOLUTION 



on such variations as are now observed to occur among living 

 organisms; (b) inferential evidence, which aposterioristically 

 deduces the common ancestry of allied organic types from their 

 resemblances and their sequence in geological time. Hence, 

 if we omit as negligible certain subsidiary arguments, the 

 whole evidence for organic evolution may be summed up under 

 three heads: (1) the genetic evidence grounded on the facts 

 of variation; (2) the zoological evidence based on homology, 

 that is, on structural resemblance together with all further 

 resemblances (physiological and embryological), which such 

 similarity entails; (3) the palseontological evidence which 

 rests on the gradual approximation of fossil types to modern 

 types, when the former are ranged in a series corresponding 

 to the alleged chronological order of their occurrence in the 

 geological strata. It is the bearing of recent genetical re- 

 search upon the first of these three lines of evidence that 

 we propose to examine in the present chapter, an objective 

 to which a brief and rather eclectic historical survey of 

 evolutionary thought appears to offer the easiest avenue of 

 approach. 



While many bizarre speculations on the subject of trans- 

 formism had been hazarded in centuries prior to the nineteenth, 

 the history of this conception, as a scientific hypothesis, dates 

 from the publication of Lamarck's "Philosophic Zoologique" 

 in 1809. According to Lamarck, organic species are changed 

 as a result of the indirect influence of the external conditions 

 of life. A change in environment forces a change of habit on 

 the part of the animal. A change in the animal's habits re- 

 sults in adaptation, that is, in the development or suppression 

 of organs through use or disuse. The adaptation, therefore, 

 thus acquired was not directly imposed by the environment, 

 but only indirectly — ^that is, through the mediation of habit. 

 Once acquired by the individual animal, however, the adapta- 

 tion was, so Lamarck thought, taken up by the process of in- 

 heritance and perpetuated by being transmitted to the animal's 

 offspring. The net result would be a progressive differentia- 



