Phyletic transformation

Figure 2.2 According to Darwin s theory of natural selection, species evolved by a mechanism of small continuous changes that today is known as phyletic gradualism. In this framework, evolutionary change can be realized by two distinct processes (A) a gradual transformation of a species without any increase in the total number of species (phyletic transformation), and (B) a gradual separation of an ancestral species in two or more descendant species (phyletic speciation).

Natural selection is Darwin s mechanism for phyletic transformation. Today this would be expressed as causes or mechanisms of evolutionary change, regardless of the diverse causes that different evolutionists would include this theory is clearly nomological-deductive. 

Phyletic gradualism (transformation and speciation) became in this way the one and only mechanism of evolution in the framework of the Modern Synthesis, and Simpson s contribution was welcome as the long-awaited reconciliation of natural selection with paleontology. 

Multiplication of species states that there is splitting of phylogenetic lineages as well as transformational change within a lineage. Hence evolutionary change includes two processes — phyletic evolution or transformation and speciation. Some workers would include extinction as a third process and others would include extinction under phyletic evolution. This theory is also nomological-deductive. 

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