84 THE LESSON OF EVOLUTION 



they are born at stated periods of life ; that genera 

 shew periods of rapid change and of persistency ; and 

 that species diverging at those periods are themselves 

 variable or persistent even if all these points could 

 be established, the reasoning from analogy seems to 

 me very feeble, and hardly to require refutation ; for 

 the two classes of facts are not in any way connected. 



Mr. A. Smith Woodward also thinks that the 

 evolution of animals shews a rhythm. He supposes 

 that the development of every group has two phases. 

 (1) A new type hides away, as it were, in some other 

 district than that in which it originated ; but it has 

 great developmental energy, and finally spreads over 

 every habitable region , displacing the effete race from 

 which it sprang. (2) The now dominant race, at 

 the beginning of its greatest vigour, gives origin to a 

 new type, which retires to some other place ; while 

 the future evolution of the dominant race is insigni- 

 ficant. 15 



These two hypotheses are different ; but 

 their authors agree in thinking that there 

 is some real resemblance between the life 

 of an individual and the life of a group ; 

 that in both there is early vigour and slubse- 

 quent decline. But when we remember that all 

 living organisms are descended from those first 

 formed in the pre-Palseozoic ocean, and that life on 

 the earth is, as a whole, quite as vigorous now as 

 when first produced, we see that the idea of the 

 necessary decline of a group in physiological vigour 



15 " Outlines of Vertebrate Palaeontology," Introduction, 

 p. xxi. (Cambridge, 1898). 



