628 



40,000 

 50.0OO 



20.000 



10,000 

 o 



ORGANIC EVOLUTION 



80,000 800,000 



APPROK. MUWBEP. OF SPECIES 

 IK) fttCEKfr FAUMA 



Fig. 25-5. The historical record of life is here shown in graphic form. The various phyla extend from the Cambrian 

 or Ordovician up to the present, and the width of the black pathway indicates the relative numbers of genera 

 in each phylum over this period of time. The upper figure represents the variety of species in each phylum in 

 fauna of the present time. 



book, millions of years were required to 

 produce the first living thing, but once it 

 was formed evolution went forward at a 

 rapid pace. It probably took longer to pro- 

 duce the first simple cell than it has taken 

 to evolve man from that first cell. Evidence 

 of living things appears for the first time 

 in the Cambrian rocks and, strange as it 

 may seem, occurs here in great abundance. 

 This must mean that once evolution started 



it went forth with a burst of speed from the 

 very beginning, because fossils are found 

 in all periods following the Cambrian. 

 There is very little proof that animals lived 

 in pre-Cambrian times, although had they 

 possessed soft body parts which do not fos- 

 silize they could have lived and died with- 

 out leaving recognizable imprints in the 

 rocks. It seems incredible, however, that 

 hard parts would appear almost sponta- 



