The theory of origin and "natural history" of the dermal nevus has derived in recent years from studies based on microscopic examination of nevus collections as correlated with age. Because the junctional nevus develops frequently in childhood and rarely in later life, it has been assumed that junctional activity must give rise to the dermal nevus by the process of "abtropfung." While this is possible, it is not the only explanation for the development. Two alternative explanations are that the junctional nevus simply disappears or that a new dermal nevus population arises later in life. Possibly both of these alternatives may be valid and may contribute to the vital statistics of the nevus population. It is always difficult to give dynamic interpretations to static observations without consideration of all appropriate possibilities, and the limitations of such data will be emphasized in the following paragraphs.
In 1949 Lund and Stobbe1