THE KINSHIP OF LIFE. 3 



plasm, which is, so far as we know, the physical basis of 

 all life; and the equally mysterious nuclear substance 

 or chromatin which in some fashion presides over all 

 the movements of the protoplasm and is the physical 

 basis of the phenomena of heredity. The same laws of 

 heredity, variability, and of response to outside stimulus 

 hold in all parts of the organic world. All organisms 

 have the same need of reproduction. All are forced to 

 make concession after concession to their surroundings, 

 and in these concessions all progress in life consists. 

 And at last each organism or each alliance of organisms 

 must come to the greatest concession of all, which we 

 call death. 



The unity in life is then not less a fact than is life's 

 great diversity. Whatever the emphasis we may lay 



upon the diversity of life, the essential 



Unity in variety. -^ r n ,. .. u c 



unity of all organisms must not be for- 

 gotten. This fundamental likeness among widely varied 

 forms stands as the basis of all classification. It is this 

 only which makes classification possible or conceivable. 

 These bonds of union, which are real as distinguished 

 from resemblances which are merely superficial or ap- 

 parent, are known to the naturalist as homology. The 

 existence of homologies is the fundamental fact in bio- 

 logical science. It has been regarded as a mystery of 

 mysteries, but this mystery assumes the form of natural 

 law in the light of the plain fact that identity of structure 

 is the simple result of identity of parentage. Homology 

 in any form is simply the stamp of heredity. In other 

 words, homd-logy means blood-relationship. The sim- 

 plest explanation is the truest and would long ago have 

 been recognized had it not been for prejudices of va- 

 rious sorts — theological prejudices that saw the image 

 of God in man only, and scientific prejudices which 

 arose from the surface study of surfaces. For it is the 



