54° 



THE QUARTERLY REVIEW OF BIOLOGY 



of such variants whenever we raise any- 

 kind of animal in quantity. 



GIANT FORMS 



One of the curious features connected 

 with the evolution of the animals in 

 practically every major group is the 

 development of giants, or of strange and 

 bizarre forms, which suddenly disappear 

 leaving no successors. 



In raising any form of animal life 

 individuals of unusual size are frequently 

 encountered. For instance, in many of 

 our moths and butterflies giants and 

 dwarfs are very readily produced. It is 

 idle to suppose that these do not occur 

 as frequently, or almost as frequently, in 

 nature. 



But if this is true, then we have an 

 adequate explanation of a curious phe- 

 nomenon characteristic of successive fossil 

 types in many different groups. It is 

 often to be noticed that in successive 

 geological horizons animals of a certain 

 type will increase in size, at the same time 

 departing more and more widely from 

 their immediate relatives, until suddenly 

 they disappear. 



Since protection from predaceous 

 enemies and from competitors of their own 

 kind usually is best afforded by increased 

 size and strength, it is to be expected that 

 of all the infinite types of variants giants 

 are perhaps the most likely to persist. 



But increase in size means a correspond- 

 ing decrease in the number of individuals 

 in the area inhabited, since each individual 

 requires a larger proportion of the food 

 supply. Decrease in the number of in- 

 dividuals means a corresponding decrease 

 in the number of variants, which become 

 simply isolated abnormalities, and hence 



results in a gradual fixation and stabiliza- 

 tion of the type through inability to 

 change. 



Once fixed and stabilized through re- 

 duction to a point where variants are i 

 simply sporadic and wholly isolated 

 individuals, an animal type becomes 

 wholly dependent on the maintenance of 

 conditions as they are, and any change in 

 these conditions results in its extinction. 



The reason why animal types have 

 persisted through succeeding geological 

 ages in the smaller and more generalized 

 forms is simply because in these there are 

 always variants in sufficient numbers so 

 that changing conditions may be met by *, 

 the development of suitable forms from 

 among these variants. 



As giants require a very large amount of j 

 food it would seem that they should 

 appear particularly within the animal j 

 groups capable of active locomotion andi 

 also with unusual ability to see or hear 

 or both. This is indeed the case. The 

 most spectacular of the giants of the 

 past are to be found among the crustaceans i 

 and the insects, the cephalopod mollusks,; 

 and the vertebrates. The giants of the 

 modern world are to be found in the same 

 groups. 



In conclusion we may say that while in 

 many of the numerous major groups of; 

 animals we can demonstrate a constanti 

 change from age to age, evidenced by an 

 increase in diversity and a more delicate; 

 adjustment to environment, among these; 

 major groups themselves we can see no 

 fundamental change whatever. Ever; 

 varying in the finer details of its manifest 

 tations, in its major features animal life! 

 has from the very first remained un- 

 changed. 



LIST OF LITERATURE 



(Editorial Note: In lieu of a complete bibliography, 

 which would obviously be too extensive to print in 

 a journal, the author has appended the following list 



of his own papers, a perusal of which will indicate 

 the steps by which he arrived at the conclusions set 

 forth in the present paper. In other words, these 



