This assertion is false since it depends on the type of selection exerted on the trait under investigation
Explanation:
Geographic isolation is caused by physical barriers such as, for example, rivers, mountains, longer distances, etc, which prevent the interchange of genetic material among populations of the same species. Over time, complete geographic isolation leads to genetic isolation among populations and the development of reproductive barriers, resulting in the separation in two species (speciation). Intermediate populations prevent speciation by enabling gene flow among populations. In consequence, intermediate populations often exhibit intermediate traits as a consequence of bidirectional gene flow; however, there are cases where a given trait is favored by non-directional selection, thereby favoring phenotypic values exhibited by marginal populations localized at the extreme distributional range of the species.
