Can the processes that account for the differentiation of populations 

 be the same ones that are responsible for the great diversity of life? 

 The efficacy of mutation, selection, migration (in the genetic 

 sense), and drift in producing different colors of Linantlms flowers, 

 geographic variants among butterflies, or species of birds has been 

 described in the preceding chapter. Now the question may be 

 asked: Is the same constellation of factors also responsible for the 

 differences among flowers, butterflies, and birds? Are these factors 

 responsible for the existence of extremely distinct clusters as well as 

 for those separated by relatively small gaps? Because of the pri- 

 marily taxonomic orientation of early evolutionary studies, this is 

 often considered to be the problem of the origin of higher taxonomic 

 categories. Some paleontologists and geneticists have felt that 

 higher categories, such as genera, families, and orders, may have 

 resulted from evolutionary processes ( macroevolution ) different 

 from those studied at the species level ( microevolution ) . It seems 

 clear from the evidence from many fields of biology that, because 

 of the immense amount of time during which evolution has been 

 taking place, there is no need to postulate other processes in addi- 

 tion to those previously discussed. 



EXTINCTION AND B I G E G R A P H I C 

 PROVINCIALISM 



The existence of extremely distinct clusters can be accounted for 

 by extinction or by inadequate geographic sampling. Of course, 

 with possible very rare exceptions such as certain fish species whose 

 entire populations seem to occur in single small springs, even the 

 most distinct clusters are made up of smaller subclusters with some 

 degree of variation among them. 



Extinction 



The sole surviving member of the reptilian order Rhynchocephalia, 

 the tuatara {Sphenodon punctatus), is found only on about a dozen 

 islets off the coast of New Zealand. The groups of individuals on 

 different islands certainly belong to different mendehan populations, 

 but the degree of genetic divergence among these populations ( and 

 the amount of interchange among them ) is unknown. Other animal 

 isolates of this sort are numerous. The strange Peruvian butterfly 

 Styx inf emails is a member of the family Lycaenidae (related to | 251 



