464 



SCIENCE 



[N. S. Vol. XXXVIII. No. 



divergence. A few examples may illustrate 

 the justification of the three terms. If out 

 of ten very similar black-haired people only 

 two become white by the usual process, whilst 

 the others retain their color, then these 

 two diverge from the rest; but they do not, 

 by the acquisition of the same new feature, 

 become more alike each other than they 

 were before. Only with reference to the 

 rest do they seem to liken as they pass from 

 black through gray to white, our mental 

 process being biased by the more and more 

 emphasized difference from the majority. 



10 Ax Bx Cx D E F 

 9 



5 



4 



3 



2 Ax Bx 



1 A B C D E F 



Supposing A and B both acquire the 

 character X and this continues through 

 the next ten generations, while in the de- 

 scendants of C the same character is in- 

 vented in the tenth generation, and whilst 

 the descendants of D, E, F still remain un- 

 altered. Then we should be strongly in- 

 clined, not only to key together C(x/10) 

 with A {x/10) and B(x/10), but take this 

 case for one of convergence, although it is 

 really one of parallelism. If it did not 

 sound so contradictory it might be called 

 parallel divergence. The inventors diverge 

 from the majority in the same direction: 

 Isotely. 



Third 'Case: Ten people, contemporaries, 

 are alike but for the black or red hair. 

 Black A turns white and Red E turns 

 white, not through exactly identical stages, 

 since E will pass through a reddish gray 

 tinge. But the result is that A and E be- 

 come actually more like each other than 

 they were before. They converge, although 



they have gone in for exactly the same di- 

 vergence with reference to the majority. 



In all three cases the variations begin by 

 divergence from the majority, but we can 

 well imagine that all the members of a 

 homogeneous lot change orthogenetically 

 (this term has been translated into the far 

 less expressive "rectigrade") in one di- 

 rection, and if there be no lagging behind, 

 they all reach precisely the same end. This 

 would be a case of transmutation (true 

 mutations in Waagen's and Scott's sense), 

 producing new species without thereby in- 

 creasing their number, whilst divergence 

 always implies, at least potentially, increase 

 of species, genera, families, etc. 



If for argument 's sake the mutations pass 

 through the colors of the spectrum and if 

 each color be deemed sufficient to designate 

 a species, then, if all the tenth generations 

 have changed from green to yellow and 

 those of the twentieth generation from yel- 

 low to red, the final number of species 

 would be the same. And even if some 

 lagged behind, or remained stationary, 

 these epistatic species (Eimer) are pro- 

 duced by a process which is not the same as 

 that of divergence or variation in the usual 

 sense. 



The two primary factors of evolution are 

 environment and heredity. Environment 

 is absolutely inseparable from any existing 

 organism, which therefore must react 

 (adaptation) and at least some of these re- 

 sults gain enough momentum to be carried 

 into the next generation (heredity). 



The life of an organism, with all its ex- 

 periments and doings, is its ontogeny, 

 which may therefore be called the subject 

 of evolution, but not a factor. Nor is se- 

 lection a primary and necessary factor, 

 since, being destructive, it invents nothing. 

 It accounts, for instance, for the composi- 

 tion of the present fauna, but has not made 

 its components. A subtle scholastic insinu- 



