Some distinctive living species clearly originated in the very recent past, during brief instants of geologic time. Thus, quantum speciation is a real phenomenon. Chapters 4 through 6 provide evidence for the great importance of quantum speciation in macroevolution (for the validity of the punctuated model). Less conclusive evidence is as follows: (1) Very weak gene flow among populations of a species (a common phenomenon) argues against gradualism, because without efficient gene flow, phyletic evolution is stymied. (2) Many levels of spatial heterogeneity normally characterize populations in nature, and at some level, the conflict between gene flow between subpopulations and selection pressure within subpopulations should oppose evolutionary divergence of large segments of the gene pool; only small populations are likely to diverge rapidly. (3) Geographic clines, which seem to preserve in modern space changes that occurred in evolutionary time, can be viewed as supporting the punctuational model, because continuous clines that record gradual evolution within large populations represent gentle morphologic trends, while stepped clines seem to record rapid divergence of small populations. (4) Net morphologic changes along major phylogenetic pathways generally represent such miniscule [sp] mean selection coefficients that nonepisodic modes of transition are unlikely. Quantum speciation or stepwise evolution within lineages is implied. (5) The known fossil record fails to document a single example of phyletic evolution accomplishing a major morphologic transition and hence offers no evidence that the gradualistic model can be valid.