Chapter X 



THE ORIGIN OF LIFE AND ITS LATER 



EVOLUTION 



EVOLUTION AND PALEONTOLOGY 



At the tail end of the discussions in this book, it is well, I think, to 

 stress once more the distinction between the origin of life and its 

 early development on the one hand, and its later evolution on the 

 other. Geologists today feel safe in stating that paleontology has 

 proven the existence of natural evolution over the last half-billion 

 years. This scientific faith does not stem so much from the fact that 

 we know all about evolution. The contrary is even true, and many 

 and varied are still the gaps in the paleontological record, both as 

 regards the bridging of deviating structures in different groups of 

 plants and animals, and the gaps caused by barren layers intercalated 

 between fossiliferous strata. Nevertheless, we do have this faith, and 

 this assumption is largely based on the evolution of our knowledge 

 of the paleontological record, since the time when theories of evolu- 

 tion became first enunciated. It is due to the fact that the many 

 lucky discoveries of linkages which were missing up to that time, 

 always confirm, be it in a general way, the theor)' of evolution. 



Of course, in detail, parentages have had to be shifted. Also, of 

 course, there have in reality always been more different kinds of 

 plants and animals in the past than we know of from the fossil 

 records. Every new find adds to our knowledge, and it follows that 

 evolution has often been more complicated in reality than had been 

 surmised by a paleontologist drawing ideal ancestry lines too much 

 schematized from too scanty a material. But although there have 

 been revisions in detail, the main lines of evolution became confirmed 

 whenever some link still missing was actually found. 



All of this applies, however, only to the later evolution of lite on 

 earth, to the period from which we have a paleontological record. 



