EVOLUTION OF SPECIES 31 



These immense changes are shadowed, though 

 very faintly, by changes that we may see occurr- 

 ing at the present day. The members of no family 

 are exactly alike : they show variations, or 

 " fluctuations," sufficiently pronounced to mark 

 one individual off from another. These fluctua- 

 tions result in some measure from the blending 

 in various proportions of the traits of the father's 

 and the mother's stock ; but there is reason to 

 believe that they are also due to a spontaneous 

 tendency to vary which is inherent in Life. 

 Variations have been observed amongst uni- 

 cellular organisms which have come into being by 

 simple cell division. There occur, moreover, other 

 more substantial variations to which the term 

 " mutation " has been attached. These are very 

 noticeable indeed. Such is a red blossom in a 

 bed of white-flowered plants ; a chicken with 

 reversed feathers. They are commonly known 

 as " sports," and are of not infrequent occurrence 

 amongst domesticated animals and plants. 



Darwin admitted these mutations into his 

 scheme, but relied for the most part upon the 

 fluctuations which, although far less momentous, 

 are of universal occurrence. Both mutations and 

 fluctuations might be useful or useless : one that 

 was useful assisted the organisms which bore it 

 in the struggle for life, enabled them to outvie 

 their competitors and procreate young in which 

 the fluctuation would be a settled hereditary trait. 

 Amongst the fluctuations to which the offspring 

 were subject would be one which advanced this 

 trait towards greater completion ; this would in 

 like manner become settled, and in this fashion, 

 during the lapse of ages, a minute pigment spot 

 might be developed into a complicated eye. 

 Fluctuations, normally spontaneous and (so to 

 speak) accidental, might in some cases be pur- 



