VARIATION IN MAN AND ANIMALS 103 



teristic which is to be selected. Nothing done to them 

 after birth, and not done to others of their family or 

 race, causes the desired characteristic ; it appears unex- 

 pectedly, almost unaccountably as an in-born quality. 

 It may be a slight difference only, not easy to take note 

 of; but if it enables those who possess it to get the 

 better of their competitors in the struggle for life, they 

 will survive and mate and so transmit their characteristic 

 to the next generation, whilst those who do not possess 

 it and are beaten in life and fail to obtain food, safety, 

 and mates, will perish and disappear, and their defective 

 strain will perish with them. 



37. Variation and Selection Among Living Things 



Selection is not a thing once done and then dropped 

 natural selection is continuous and never-ending, 

 except in rare and special circumstances, such as man 

 may bring about by his interference, and then it does 

 not really cease but only changes its demand. The 

 characteristics of a race or species are maintained by 

 natural selection, just as much as they are produced 

 by it. Cessation of a previously active selection (which 

 is sometimes brought about by exceptional conditions) 

 results in a departure of the individuals of the race, 

 no longer subject to that selection, from the standard 

 of form and characteristics previously maintained. To 

 understand this, we must consider for a moment the 

 great property of living things, which is called 

 " variation." 



No two animals, or plants even, when born of the 

 same parents, are ever exactly alike. Not only that, 

 but if we look at a great number of individuals of a 

 race or stock, we find that some are very different from 

 the others, in colour, in proportion of parts, in charac- 



