182 The Mechanism of Evolution in Leptinotarsa 



methods by which groups might originate in nature, and if possible detect or 

 produce such origins in experiment in nature. 



The idea of the role of crossing in the production of natural groups in a state 

 of nature as an agency of any importance is of recent origin. The older writers 

 admitted the possibility of crossing in nature, but, following Darwin, thought of 

 it as incidental to other operations, often as the product of a destruction of the 

 barriers of interspecific sterility, while in the minds of all the main type of 

 production has been that which was the product of dichotomy of some ancestral 

 line, either by slow or rapid processes of separation. This conception is retained 

 in De Vries's theory of species production, the separation being one of rapidity 

 instead of by slow transformation. Since the rediscovery of the Mendelian reac- 

 tion and its verification in numerous instances, the experiences and expressions 

 of opinion have been increasingly towards the idea that it may be possible that 

 species in nature are of hybrid origin. One of the first of the modern writers to 

 express this opinion was Morgan, and it has been raised also by others, while the 

 findings of many observers have shown that crossing is going on in nature 

 between natural groups, but to what extent no one has any information. 



The great problem in all species origins has been that of the rise of the initial 

 group, and the discussions have to considerable extent centered around the fate 

 of the first ancestor and what was necessary for this lone individual or pair to 

 encounter or overcome in order to survive and produce progeny in the location. 

 It seems to me that some of the results of these experiments in crossing species 

 give what may be a method of the origin of groups in nature which under the 

 conditions of existence would breed true without limit and which might rarely 

 throw a sport as the result of its hybrid nature and be in all respects a true- 

 breeding species. Any one of a number of the pure-breeding fixed heterozygous 

 lines that have appeared in my cultures would have survived in nature and gone 

 on as effective members of the fauna of the location in which they arose. This 

 appears as a possible method of origin ; I do not have any data as to how probable 

 it is, nor do I know of any method of deciding whether species in nature have or 

 have not arisen by this or any other method. This type of origination seems logi- 

 cal and suggests that it is of common occurrence in the production of natural 

 specific groups. 



Precisely the same general type of sequence of events is productive of much of 

 the specific diversity in the nonliving series in nature; the specific thing, com- 

 pound, mineral, or complex rock is the immediate product of the reactions of the 

 interacting combining materials or factors of composition, and the product 

 appears fully developed and in amount corresponding to magnitude of the oper- 

 ations. If organisms are complex compounds whose operations are purely phy- 

 sical in nature, I see no a priori reason why in the origination of specific organ- 

 isms the process should not be in the main of the same order, and its rise follow, 

 as a group of varying size, entirely dependent upon the magnitude of the origina- 

 tion process. In this way it is possible to conceive of and possibly produce 

 experimentally the rise of groups in nature by processes akin to those I have wit- 

 nessed in the laboratory, giving pure-breeding, distinctive, physiologically iso- 

 lated groups. The conception and experience is interesting and worthy of 

 extended test in nature and in laboratory experiment. That it is not an idle one 

 is fully shown by the products derived in the experiments described in the preced- 

 ing chapters. 



