160 Kansas Academy of Science. 



The claims of the mutation theory are thus as extravagant in 

 that direction as that of natural selection in the other. The truth 

 lies in the medium ground, as usual. Darwin anticipated this idea, 

 to a degree, when he said (Or. Sp., I, p. 313): 



"Everyone who believes in slow and gradual evolution will, of course, 

 admit that specific changes may have been as abrupt and as great as any 

 single variation which we meet under nature, or even under domestication. 

 But as species are more variable when domesticated or cultivated than under 

 their natural conditions, it is not probable that such great variations haVe 

 often occurred under nature as are known occasionally to arise under domes- 

 tication. . . . My reasons for doubting if this can occur, and for entirely 

 disbelieving that species can change in the wonderful manner that is claimed 

 by some, are as follows: According to our observations, abrupt and strongly 

 marked variations occur in our domestic productions, singly and at long 

 intervals of time. If such occurred in nature they would be liable to be lost 

 by accidental causes of destruction and by subsequent intercrossing, as is 

 the case under domestication unless special efliorts are made for its preser- 

 vation. Hence it is necessary to believe that several similarly changed in- 

 dividuals appeared simultaneously in the same district." 



Again (p. 316): 



"It is claimed that the sudden appearance of new species in geological 

 formations supports the theory, but the admittedly imperfect record of the 

 rocks prevents that evidence from being of any value. ... He who 

 believes that some ancient form was transformed suddenly, through internal 

 force or tendence, will be almost compelled to assume, in opposition to all 

 analogy, that many individuals varied simultaneously. . . . Against 

 such abrupt changes, embryology enters a strong protest. It is notorious 

 that the wings of birds, the legs of horses and other quadrupeds, are indis- 

 tinguishable at an early embryonic period, and that they become differenti- 

 ated later by insensibly fine steps. . . . Hence it is that it is incredible 

 that an animal should have undergone momentous and adrupt transformation 

 and yet should not bear even a trace in its embryonic condition of any sudden 

 modification, every detail in its structure being developed by insensibly 

 fine steps." 



A striking book of the past year was that on " Evolution and 

 Pathology," by D. von Hanseman (Sci., Dec. 3, 1909, p. 826), who 

 takes the very original view that, as a ball upon an inclined plane 

 is prevented from rolling by some external hindrance, so species 

 having an inherent and continual tendency to vary are prevented 

 from changing by reason of external conditions. Adaptation means 

 the establishing of an equilibrium between the internal forces and 

 external conditions. The phenomena usually credited with bring- 

 ing about variations are here regarded as effective agents in check- 

 ing the inherent tendency to vary. This results, in the long run, 

 in the power for variation being weakened or lost, so that in the 

 highest animals we find great fixity of types. The conditions 



