26 THE LESSON OF EVOLUTION 



been unfavourable. Or, if this also was suitable, there 

 might not have been a due proportion of the various 

 elementary substances to allow the continuous exist- 

 ence of life ; for these different factors are in no way 

 related. 



It may be urged that, among an almost infinity of 

 worlds, we might expect to find an almost infinite 

 number of different combinations ; and it so happens 

 that the earth contains exactly that combination 

 necessary for organic development. But the objection 

 is not a valid one, because each system of sun and 

 planets in the universe has, no doubt, been developed 

 under identical physical laws and from identical sub- 

 stances. They are, more or less, repetitions of each 

 other, so that the number of systems makes no 

 difference, and the earth can only be contrasted with 

 the other planets belonging to our solar system. 

 Now, have the other planets a similar composition to 

 the earth ? As they shine with light reflected from 

 the sun, the spectroscope does not give us any infor- 

 mation on this point, and we can only speculate. As 

 the composition of the sun differs considerably from 

 that of the earth, we have no reason for supposing 

 that all the planets are similar. On the contrary, if 

 the meteoritic hypothesis be true, and if the meteor- 

 ites which now fall on the earth are samples of the 

 meteoritic cloud out of which the solar system was 

 formed, the planets cannot have identical compositions, 

 because the meteorites differ considerably from each 

 other, and no two aggregations of them would give 

 rise to similar bodies. If, on the other hand, the 

 present meteorites are not surviving samples of the 

 original cloud, but have been drawn into the solar 



