The Background of Genetics ii 



and the hybridization theory provide suggestions on 

 this point, but the suggestions are hardly satisfactory. 

 For question 2 rather distinct answers are provided by 

 Lamarck, Darwin, De Vries, and the orthogenesis 

 theory. It is in answering question 3 that the isolation 

 theory and the hybridization theory have their chief 

 value. Question 4 is indirectly answered in one way by 

 Lamarck, and indirectly answered in another way in 

 the orthogenesis theory, while all the other theories 

 plainly call upon natural selection to answer this ques- 

 tion. If the theories are to be compared, it can safely 

 be done only after some such analysis as this. 



Third, discussion of evolutionary theories usually 

 leads to the realization that more exact experimental 

 evidence is needed before much further progress can be 

 made in solving the problems of evolution. Such has 

 been the actual history of the case, for, with the begin- 

 ning of the twentieth century, the study of evolution 

 culminated in, and became diverted into, genetics, the 

 experimental study of inheritance. Of course genetics 

 has not answered all of the questions that have presented 

 themselves in connection with evolution, but many criti- 

 cal and suggestive findings have been made, as will be 

 seen in the following chapters; and unquestionably 

 genetics will contribute a great deal more in the next 

 few decades. 



