8o PROBLEMS OF EVOLUTION 



the scientific world upon them great things depend. I do not 

 myself believe these phenomena seriously menace the theory of 

 the origin of species through Natural Selection. Even in the 

 present state of our knowledge they may be to a great extent 

 explained, and we may hope that they will become still less 

 formidable as investigation progresses. 



They may (i) Some of these characters are mere vestiges, useful once, 

 vestiges but which have been reduced to very small dimensions because 

 they had ceased to be useful. Such are the scales between 

 florets : no doubt, they were once bracts. In Hypoch&ris they 

 linger on, in Leontodon they have completely disappeared. If 

 we could only trace back the line of descent step by step, 

 many features that are now too small to help or to hinder 

 might be found to have been once the sheet anchors of their 

 species. In every case, it must be noticed, they are at least 

 harmless ; at any rate, they do not prevent the species from 

 living and thriving. 



or (z) due (2) The principle of correlated variation may here help us a 

 0n tJon g reat deal. Correlation, like Mesopotamia, is a blessed word : 

 the evolutionist calls it to his aid when in dire distress. Here it 

 may be of real assistance. 



Different parts in an organism are often closely related. If a 

 child has long hands, we prophesy that he will be tall. Great 

 size of head in the offspring must mean largeness of pelvis in 

 the mother. Very abnormal development of teeth in man goes 

 along with a corresponding growth, or else a deficiency, of hair. 

 The interdependence of different parts is shown by the putting 

 out of the tongue during the performance of some act of manual 

 skill, or by the difficulty of moving the left hand horizontally 

 to and fro and at the same time the right hand vertically up 

 and down. 



The known examples of correlation are many, though doubt- 

 less but a fraction of the number that exist. Did we know them 

 all, we might be able to explain a great deal that is as yet inex- 

 plicable. For instance, the dark-skinned races are better adapted 

 to hot climates than the light-skinned, and it is held by some 

 authorities that it is not the dark pigment that confers this 



