i8 POPULAR SCIENCE MONTHLY. 



in any evolutionary sense. The wonder is not that organisms build 

 differently with different materials, but that they are able to build with 

 the same materials such infinite diversity of form and structure. 



Conditions Favoring Evolutionary Progress. 



That with adequate materials supplied by abundant food a species 

 would be able to exhibit a larger range of variation, is undoubtedly 

 true, and offers no difficulties in a kinetic theory. The more favorable 

 the conditions or the more successful the adaptation, the more numer- 

 ous the individuals; also the more extensive would be the manifesta- 

 tions of the variational possibilities of the species, and the more rapid 

 ^■he resulting evolutionary progress. If static theories of evolution 

 were correct numerical increase would not favor evolutionary change 

 because it would diminish the chances of the segregation on which the 

 preservation of variations has been thought to depend. 



The most advanced organic types — those which have traveled 

 farthest on the evolutionary journey — are not natives of islands, but 

 of continents. The greatest and most rapid evolutionary progress has 

 not been made among organisms of localized distribution, but among 

 those having facilities for wide dissemination and free interbreeding. 

 Large species move faster than small. Insular species become diverse 

 from their continental relatives mainly because they are left behind 

 by the latter rather than because isolation favors evolution. 



Segregation did not denote evolution either in the remote or in the 

 more recent past. As the geological record is followed backward the 

 more generalized types are found to have more generalized distribution, 

 and if in former ages evolutionary changes were more rapid than at 

 present in any particular group this may well be correlated with a period 

 of very favorable conditions permitting the simultaneous existence of 

 vast numbers of individuals in species continuous over large areas. The 

 later subdivision of these generalized types betokens less favorable cir- 

 cumstances which reduced the numbers or otherwise localized the distri- 

 bution, and thus segregated the new groups. The birds outnumber the 

 reptiles,* the insects the myriapods, the composites the palms. The 

 better the facilities for distribution the more rapid the evolution. 



On the other hand the greater the localization and the fewer the 

 individuals the slower the evolutionary progress of a species, and the 

 more uniform the characters. Their supposed constancy leads systema- 



* ■ 



Mr. F. A. Lucas calls my attention to the interesting fact that a sim- 

 ilarly accelerated development occurred among the pterodactyls, a second 

 winged group of reptilian ancestry. In the Jurassic and Cretaceous periods 

 pterodactyls attained a rapid and extensive differentiation of genera and 

 families. Likewise the early Eocene mammal types appeared very abruptly 

 and had a very wide distribution. 



