EVOLUTION CONKLIN 217 



The older evolutionists, for example, undertook to show by what 

 Iransformations of the developed body an annelid or arthropod could 

 be converted into a vertebrate. It w^as supposed that the invertebrate 

 turned upside down, its mouth closed up and a new mouth formed, 

 and many other changes occurred which would be absolutely im- 

 possible in any developed animal. Similar impossible translocations 

 of organs of adults had been proposed to explain the origin of inverse 

 asymmetry, as for example in those rare cases in man where the 

 heart is found on the right side instead of the left and all other 

 asymmetrical organs are reversed in position. When it was dis- 

 covered that such inversions of all the organs of sinistral as com- 

 pared with dextral snails could be traced back through the embry- 

 ology to the early egg cell, it was evident that this inversion was due 

 to relatively slight changes in the locations of cytoplasmic substances 

 in the egg cell ; such changes are now known to be caused, in the last 

 analysis, by genes. Similarly, when it was discovered that the loca- 

 tion of the principal organs of several different phyla could be traced 

 back to the pattern of localization of special substances in their eggs, 

 I suggested that relatively slight changes in the localization of these 

 substances would bring about the characteristic differences in the 

 location of the organ systems of vertebrates as compared with inver- 

 tebrates. Thus, instead of turning a developed worm or arthropod 

 upside down, and making many impossible translocations of its 

 organs, it would be relatively simple to convert one type into another 

 by translocations of cytoplasm within a single cell, such changes 

 ultimately being caused by gene activity. Unfortunately, this sug- 

 gestion, like that of Goldschmidt just mentioned, is at present without 

 experimental proof. 



V 



Adaptations have always been the chief marvel of the living 

 world and their method of origin is still the greatest problem of 

 biology. The only natural explanation that has as yet been estab- 

 lished is Darwin's principle of the elimination of the unfit and the 

 survival of the fit. There is abundant evidence, both observational 

 and experimental, that this principle is true, but when we load upon 

 it the obligation of explaining all the marvelous adaptations and 

 combinations of adaptations that every living thing possesses, the 

 doubt arises as to whether this principle alone can support the 

 enormous burden. I have long felt, along with Cope, Osborn, and 

 many others, that some additional factor is needed to explain such 

 universal adaptations. And Darwin himself felt the force of this, 

 for he said that he never thought of attempting to explain the 

 origin of such a complex and wonderfully coordinated structure as 



