THE ORIGIN OF SPECIES. 59 



more perfect than the requirements demand. The almost exact re- 

 semblance between the right and left sides of the body, while advan- 

 tageous up to a certain point, is often far more perfect than com- 

 petition requires. In fact we find the Darwinians often dodging this 

 consideration, and referring the results to ' the laws of growth/ etc. 

 But if these ' laws of growth ' exist why may they not have also 

 carried the perfection of any organ far beyond the point at which 

 the test of survival stops? 



We meet with a somewhat similar case in the distribution of color 

 over the bodies of animals. Granting that in some cases the presence 

 of colors, after they have appeared, may be of some use to the animal 

 or plant, yet the wonderful symmetry of distribution, and the gradual 

 shading of the colors is often far more regular than appears to be 

 required. This result also will no doubt be ascribed to ' the laws of 

 growth/ but if we once admit such a principle at work, why bring in 

 any other outside law to explain the perfection of those characters that 

 are useful to the organism? If when a new species appears its colors 

 happen to be so distributed that the individual gains some advantage, 

 so much the better ! If the color does not count one way or the other, 

 then it does not enter into the problem of survival; but if it exposes 

 an animal to a greater risk than it can surmount, that species will fail 

 to hold its own. The same regularity and graduation of color exists 

 also in animals that are microscopic, and no one thinks of accounting 

 for these conditions through selection. Why then do we need a special 

 explanation when the animals are so large that they attract our at- 

 tention ? 



A number of writers, of whom Eimer is perhaps the most prominent, 

 have insisted that evolution progresses along certain definite lines that 

 are quite independent of selection of individual variations. The pro- 

 cess has been called orthogenesis. Certain aspects of this view are in 

 full accord with the theory of the survival of definite variations; for, 

 we find, in fact, one of the most characteristic features in the appear- 

 ance of definite variations to be that the same forms appear over and 

 over again, showing a definite tendency to vary in certain definite 

 directions. A striking case of this sort is that of the japanned peacocks 

 described by Darwin, and of the mutations of the evening primrose 

 described by de Vries. If future work can show that a change in a 

 given direction is likely to be followed by others in the same direction, 

 amongst some at least of the offspring, the process will have much in 

 common with the process of orthogenesis. If this process should be 

 in the direction of making some particular organ more perfect than 

 the conditions demand, the new type may persist along with the parent 

 form also, which it need not replace. If, on the contrary, the new 

 acquirement unfits the new species for its environment the new species 



