26 CHANGE 



are largely composed of materials so stable as, 

 in the form of coal, to have outlived many 

 geological ages. But, in plants as in animals, the 

 vital energy, which enables them to live and to 

 grow, resides in delicate tissues which are in pro- 

 cess of constant change. When change ceases, 

 when the vital energy fails to preserve a whirl of 

 metamorphosis, the organism becomes clogged 

 and death ensues. This is the greatest change of 

 all : one individual is obliterated in favour of 

 another. Why, amongst the various kinds of 

 plants and animals, should one find such extra- 

 ordinary differences in the normal duration of 

 life ? Why should some plants be annuals, whilst 

 others can live through several centuries ? Why 

 should a sea-anemone live for fifty years, whilst 

 the vitality of a dog is almost exhausted in ten ? 

 We do not know. We should expect to find some 

 connection between the length of an organism's 

 life and the period within which it attains sexual 

 maturity. In some classes of plants and animals 

 we can trace such a connection : the northern 

 races of mankind appear to have gained in longe- 

 vity by being late in reaching the age of puberty. 

 But this theory is opposed by a host of contra- 

 dictions, as are indeed almost all attempts to 

 bring within the definition of a rule the multiform 

 vagaries of Life's activity. 







The life of an individual may thus be compared 

 to the unrolling of a cinematograph film : so also 

 may be the life of a community, but in this case 

 the illumination flickers with the alternate flashes 

 and darkness of birth and death. And, by a 

 peculiar limitation of reproductive action, it is 

 ensured that each runner in the race differs in 

 constitution from those who give place to him. 



