N0.55S] CAUSES AND DETERMINERS 



357 



to one a certain chromosome could be added), this egg 

 would now produce an animal of the other sex. The 

 question is thus purely an experimental one. Of the 

 enormous number of conditions necessary for the pro- 

 duction of the sexual characteristics, this assertion 

 specifies one, which happens to be practically interest- 

 ing to us. We trace the difference in sex between two 

 individuals back to a difference between the two eggs 

 from which they came. We may then trace the differ- 

 ence between the eggs back to differences between the 

 sperms; the latter to differences between the chromosome 

 groups of the parents, and the process of tracing back 

 is limited only by our knowledge. All these preceding 

 differences (and any others that may yet be found to 

 cause a difference of sex) are equally sex determiners; 

 the discovery of one kind of sex determiner (in our sense 

 of determiner) does not preclude the discovery of a 

 thousand others. 



B. Some assert that the brown color of the skin (or 

 some other color characteristic) is hereditary; others 

 dissent, asserting that it is due to oxidation of a certain 

 chemical compound, or to exposure to the sun. 



Applying rule 2, when we compare individuals that 

 have lived under the same conditions and find one (a) 

 dark, the other (b) white, we must conclude that the dif- 

 ference is hereditary, in the sense of determined by a 

 difference in the germ cells. But this difference in the 

 germ cells may be of such a nature as to prevent oxida- 

 tion in one case, while permitting it in the other; it is 

 then likewise true that the cause for the color is oxida- 

 tion. The same individual a that is dark might perhaps 

 not be so if not exposed to the sun ; it is then true that 

 exposure is the cause of the color. All these statements 

 as to causes are elliptical, and all are equally true; at 

 which one we arrive depends on what comparisons are 

 made; what differences we are accounting for. 



C. Some assert that the nucleus is the ' ' bearer of the 

 hereditary qualities"; others deny this with ridicule. 



