648 



ORGANIC EVOLUTION 



continuing burst of speed in the produc- 

 tion of new genera that has been maintained 

 up to recent times. Only within the past 

 10 milhon years have there been any signs 

 that indicate the peak has been reached 

 and passed. 



An interesting feature of the rates at 

 which new genera are produced in verte- 

 brate groups is that each has a peak fol- 

 lowed by a decline. Starting with the jaw- 

 less fishes, which are the lowest in numbers 

 of new genera and the first to appear in 

 geologic time, each succeeding peak is 

 higher than the preceding, that of the am- 



phibians being higher than the jawless and 

 cartilaginous fishes, that of the reptiles be- 

 ing higher than the amphibians, and that 

 of the last, the mammals, being the highest 

 of all. If the mammals have passed their 

 peak in the production of new genera, per- 

 haps they are on their way out. In that 

 event, if historical evolution repeats itself, 

 there must be some other group of animals 

 coming up. Careful studies may make it 

 possible to predict which group will suc- 

 ceed us as the dominant animals on the 

 earth. We may even be able to do some- 

 tliing about it! 



