‘Apical displacement’ is the name given to a set of sound changes in the Dravidian family, whereby alveolar and retroflex consonants which occur as Cj in Proto-Dravidian stems of the type *(Ci)VCj-V ... shift their position to produce structures of the type *(Ci)CjV- ... in a well-defined subgroup of languages, viz. Telugu, Gondi, Koṇḍa, Kui, Kuvi, Pengo, and Manḍa. With the help of a computer analysis of relevant etymologies, it has been shown that apical displacement affected less than a dozen items at a common stage of the above subgroup. The rules gradually spread to the rest of the lexicon over the following two millennia, and the change is still in progress in some languages of this subgroup. It has been demonstrated that, of the items which fulfill the structural conditions of the change, 72% are covered by it in Kui; about 63% in Kuvi, Pengo, and Manḍa; but only about 20% in Gondi and Koṇḍa. A chronological layering of lexical items is established in terms of particular combinations of languages which share the cognates-with-change. Areal diffusion is characterized as the gradual lexical spread of an inherited rule—as opposed to the traditional notion of shared innovation, which is marked by shared rules in shared innovative cognates. A large class of exceptions to sound change at any given point of time can arise when the change has not yet affected the entire eligible lexicon.