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 
