^VID^NCE CONCERNING INVOLUTION. II9 



conclusions warranted from his point of view, but not from that of others. 

 So, too, the advocate of orthogenesis, following Eimer, selects stages in varia- 

 tion here and there, and isolated facts of distribution, and draws sweeping 

 conclusions therefrom. The supporters of selection can see no possibility of 

 other methods of evolution, and the advocates of mutation are wildly enthu- 

 siastic over their newly discovered treasure. 



The only conclusion regarding the method of evolution that, from an im- 

 partial standpoint, I am able to draw from this investigation of variation and 

 distribution is that we can get no undoubted evidence to warrant a decision in 

 favor of any one hypothesis more than another. We can interpret the condi- 

 tions found by any of the current hypotheses; but explaining a condition by 

 an hypothesis is not the same as that the conditions found are evidence in 

 support of an hypothesis, although it is often so used. Although it is conclu- 

 sive that no direct evidence of value or reliability concerning the method of 

 evolution is to be derived from distribution and variation, three suggestive 

 facts come out in the clearest possible manner : First, that species differentia- 

 tion and variability have followed in the same lines or directions of evolution 

 as is shown in distribution and variation; second, that three forms, melano- 

 thorax, august ovittata, and rubicunda, arise as extreme variations and are 

 stable forms; third, that there is strong evidence, in the case of multitceniata 

 and decemlineata, against the idea of the slow modification of a species by the 

 incorporation into its constitution of fluctuating place or geographical varia- 

 tions. These facts have been investigated experimentally and otherw^ise and 

 the results will be presented later. 



The study of distribution and variation, although not affording conclusive 

 evidence concerning the method of evolution, does give rather complete and 

 reliable data upon the probable phylogenetic development of the genus, and 

 also information concerning the limits, directions, and laws of variation, dis- 

 tribution, and migrations. This information is important, nay, indispensable, 

 in the study of evolution, in that it shows us what the natural history of the 

 material under investigation has been. This knowledge of the natural history 

 of the genus I regard as of fundamental importance; and it can not, I believe, 

 be neglected without seriously impairing the value of researches in experi- 

 mental evolution. 



The conclusions to be drawn from this study of distribution and variation in 

 the genus Leptinotarsa are that species differentiation, as far as it is possible to 

 determine, has been definite and not promiscuous, and that all variations are 

 definite and not promiscuous, and also that both species differentiation and 

 all variations are in the same directions and are in a most remarkable manner 

 correlated with natural features of the general habitat. The data of distribu- 

 tion and variation can give no real basis for determining the method of evolu- 

 tion, nor does it enable us to arrive at the causes thereof. We can arrange 

 the species of the genus in series, and opposite them place climatic and other 

 9— T 



