CONWAY ZIRKLE 



University of Pennsylvania 



OGIC^^ 



Chapter 1 



Early Ideas on Inbreeding 

 and Crossbreeding 



In tracing the historical background of a great scientific advance or dis- 

 covery, the historian nearly always has the opportunity of showing that the 

 scientists who receive the credit for the work are really late-comers to the 

 field, and that all the basic principles and facts were known much earlier. 

 Finding these earlier records is always something of a pleasure; comparable, 

 perhaps, to the pleasure a systematist experiences in extending the range 

 of some well known species. 



The historian may be tempted, in consequence, to emphasize these earlier 

 contributions a little too strongly and to re-assign the credits for the scientific 

 advances which have been made. In the present state of the history of sci- 

 ence, it requires only a little searching of the records to discover contributions 

 which have been overlooked and which are very pertinent to the advance 

 in question. This wealth of data, which accumulates almost automatically, 

 seems to deserve emphasis. But great steps forward generally are made 

 not by the discovery of new facts, important as they are, or by new ideas, 

 brilliant as they may be, but by the organization of existing data in such 

 a way that hitherto unperceived relationships are revealed, and by incor- 

 porating the pertinent data into the general body of knowledge so that new, 

 basic principles emerge. 



For example, even so monumental a work as Darwin's Origin of Species 

 contains few facts, observations or even ideas which had not been known 

 for a long time. The work of many pre-Darwinians now appears important, 

 especially after Darwin's synthesis had shown its significance. Of course, 

 this does not belittle Darwin in the slightest. It only illustrates the way 

 science grows. 



The emergence of the scientific basis of heterosis or hybrid vigor is no 



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