ORIGIN OF SPECIES 101 



ciple later on. When he surveys the ^immense variety cf 

 animals and plants, the question naturally' .presents itseJf^to 

 his mind, Why so many? How' did this vast array come , 

 into existence ? ^ ^ //, * ', i ' * Uf ;',; i 



Certain facts are quite clear. The conditions which have 

 obtained on the globe since first it was habitable by living 

 things have undergone great progressive changes. They 

 have also fluctuated from time to time. Plants or animals 

 which could live upon the earth or upon a particular part of 

 the earth in one geological epoch would have been killed 

 off in the next. Fossil-forms make their appearance and 

 disappear in successive strata. As stratum follows upon 

 stratum the number and variety of fossils increases, and the 

 specialization of their structure also increases progressively 

 from period to period. 



No one who knows these facts can fail to draw the 

 conclusion that transmutation of species in the direction of 

 improvement or evolution has occurred. The question 

 which biologists are debating at the present time is, What 

 is the cause of evolution ? 



Lamarck recognised that the conditions of life, the envi- 

 ronment, cause changes in the individual. He supposed 

 that these changes, being transmitted to the offspring, lead 

 to progressive transmutation. 



Darwin laid stress upon the fact that in the struggle for 

 existence Nature encourages only the more fit. As all but 

 the more fit die out without reproducing their kind, the 

 fitness of the species which survive progressively increases. 



The great question now at issue is : What is the cause of 

 the initial variation which gives to Nature a diversity of 

 material, less fit, equally fit, and more fit, from which to 

 select ? 



The only explanation of variation is based upon the 

 " Lamarckian factors," or the proposition that the increased 

 growth which use induces is transmitted by a parent to its 

 offspring. Improvement is, from this point of view, the 



