48 FOOT-NOTES TO EVOLUTION. 



plants had their origin in pre-existing forms more or 

 less different, we may presume this to have been true 

 of man also. That it is true of man in fact we know, 

 for not many thousands of years ago our ancestors in 

 Europe were barbarians, cave dwellers, lake dwellers, 

 and dwellers in hollow trees, using only the rude imple- 

 ments they shaped from metal and flint. The origin of 

 civilized man from barbarous man gives the clew to the 

 origin of barbarous man from forms still less specialized. 

 The question of the origin of man, though perhaps 

 the most interesting problem in science, offers to the stu- 

 dent of Nature peculiar difficulties. Materials for exact 

 knowledge are few and prejudices are strong, and all 

 tendencies favour an immediate decision on doubtful 

 points, though the evidence be far from sufficient. Of 

 not one man, nor monkey, nor bird, nor beast in half a 

 million does a trace remain after a thousand years not 

 a bone, nor a relic, nor a thought. Living on the sur- 

 face, we crumble into dust ; and the current phases of 

 human life, a few centuries out of hundreds, are all of 

 man's history we surely know. Many links are missing 

 still, and most of these we can never find. Our early 

 ancestry we can best infer from our knowledge of the 

 embryonic history and mental development of the man 

 of to-day. 



But if anything in science is certain, it is that homol- 

 ogy is a fact, and that it has a meaning. Among us 

 backboned animals, all structures, all 

 functions, and all mental operations 

 show distinct homologies. The essence 

 of the development theory is this : Homology is the 

 stamp of heredity. Homology means blood relation- 

 ship. No other meaning of homology has ever been 

 shown, nor is there the slightest evidence that any other 

 interpretation is possible. Blood relationship implies a 



