R^I^ATION TO IJNVIRONMEJNTAL C0MPI.E:XE:S. 5/ 



the edapbic factors with which the species are most closely correlated. 

 Each of the groups in the genus represents a line of specific differentiation 

 which has in the main been brought about in a savanna habitat, but as far 

 as anything that can be discovered in the distribution of the beetles is con- 

 cerned, it is impossible to say whether this specific differentiation is due to 

 the direct influence of the environment, to selection, to the effects of isola- 

 tion, or to segregation. It would be an easy matter to build up from the distri- 

 bution of the species of this genus a good argument in support of the idea 

 that the species have arisen through the action of isolation and segregation or 

 by selection. Either or both may be responsible for the conditions found, but 

 as far as I am able to discover there is not one whit of evidence to indicate 

 which. 



The distribution of the species does, however, indicate in the strongest 

 terms that there has been no discontinuity in the evolution of the genus, 

 and in the absence of positive evidence to the contrary we may safely hold 

 that the theory of mutation and segregation in fittest environment can not in 

 this instance be used in the explanation of the distribution and dissemina- 

 tion of Leptinotarsa. It matters little whether specific differentiation has 

 been rapid or extremely slow, and of this we have no means of gaining 

 information, but of the continuity of the dispersion and species formation 

 there is in this case not the least doubt. 



The present geographical distribution of a group of animals is the result 

 of a long series of processes, of action of organism upon organism, and of 

 environment upon organism. From our study of the distribution of these 

 beetles we have gained information as to what the geographical history of 

 the genus has probably been, what forces were most active in the distribution 

 of the group, and the extended correlation existing between distribution, 

 specific differentiation, and environment. From this we get a general view, 

 a clue here and there, of what may perhaps be of vital importance in evolu- 

 tion. At no point are we able to put our finger upon any one fact and say 

 with any certainty that this is the result of that factor in the environment 

 or of any method of evolution. The facts presented in this chapter, those of 

 geographical distribution, become more significant when considered in rela- 

 tion to the facts to be presented in the next chapter, on "Variation." 



