THE KINSHIP OF LIFE. 49 



common action of heredity, and a common heredity is 

 the only source yet known for the likenesses we call 

 homology. 



I resemble my neighbour so closely that people say 

 we look like brothers. My little boy shows similar ex- 

 actness of homology to me, and people say that he is 

 the very image of his father. My neighbour on the left 

 shows wider divergencies, but then he too is evidently 

 an Anglo-Saxon. Angle or Saxon, we were all of one 

 blood not many centuries ago. Still farther away the 

 whole Aryan race becomes one, and we are willing in 

 Adam to recognise our homology even with our poor 

 relations — the Bushman and the Hottentot. But still 

 poorer relations we have, and they too carry on their 

 faces the unmistakable evidences of kinship by blood. 

 In every bone and muscle my dog shows his likeness to 

 me, and even in every function of his feeble little brain 

 the resemblance is apparent. We have no explanation 

 of such homologies other than that of kinship by blood. 

 For this reason we know that the various races of men 

 and the various species of monkeys have some time had 

 a common ancestry. For this reason we believe that at 

 a period of time far back in the geological record all 

 vertebrate animals sprang from a common stock. We 

 have substantially the same evidence, differing only 

 slightly in degree, for believing that my dog and my- 

 self are related by blood in some form of distant cousin- 

 ship, as there is to show a similar relationship between 

 myself and any one of my neighbours. In neither case 

 can we secure proof by appeal to history. Our records 

 go back for a few generations only, and the great past 

 is lost. In either case our acknowledged kinship is only 

 an inference based on known facts of heredity and 

 homology. 



No two groups can show homologies with each other 



