ARGUMENTS FOR EVOLUTION 139 



Why should all this uniformity of type exist amongst 

 so much lesser diversity, except as a result of evolution 

 from common ancestors ? Agassiz used to say that it 

 might represent not common descent, but common 

 origin in the mind of a Creator. One may note the 

 evolution of pottery in a large museum, and refer the 

 modifications to their common source in the mind of 

 man. The idea is a fascinating one, but no modern 

 naturalist accepts it in place of evolution ; though he 

 may sometimes ask himself whether there has not been 

 a creative influence guiding the evolutionary process. 



4. We can say of the similarity of structure just de- Remnants of 



T, , , . . .... . ancient 



scribed that it is at any rate functionally appropriate, structures 

 Whatever its origin, it serves the purposes of the crea- 

 tures. There are, however, other similarities which 

 may not be thus explained. We frequently find vestigial 

 structures, which not only possess no function, but, as 

 in the case of the human appendix vermiformis, may be 

 actually detrimental. A little projection on the in- 

 wardly folded margin of the human ear appears to repre- 

 sent the tip of a pointed lobe which existed in an ances- 

 tor. The horse wrinkles the skin of its neck to drive 

 away flies, using a muscle which exists in us only as a 

 very thin and useless layer of tissue. We no longer 

 cock our ears like a dog or a horse, but remnants of the 

 -muscles for this purpose remain, and some persons can 

 use them to a certain extent. 



5. Still more astonishing is the evidence from embry- oidcharac- 

 ology. The human embryo, long before birth, exhibits 181 



structures on the side of the neck corresponding to the embryo 

 gill slits of early vertebrates. They are inexplicable 

 except on the view that a remote ancestor was aquatic. 

 The slits divide the gill arches, and it is from one of 

 these that the lower jaw develops. Embryologists be- 



