How evolution can be channeled by intrinsic processes such as genetic and developmental networks is a key issue in evolution. Studying the phenotypic variation in a population can shed light on these constraints, because this variation, being the product of these genetic and developmental processes, is the target of both selective screening and random sampling. It could thus act as a “line of least resistance to evolution”. Based on morphometric analysis of molar and mandible shape in several fossil lineages and modern groups of murine rodents, we illustrate here the questions that can be addressed based on this framework. The role intrapopulational variation as line of least resistance to evolution is validated on several lineages. The existence of such preferential direction of evolution can contribute to explain cases of parallel evolution.  The underlying mechanisms can be the sharing of similar genetic/developmental pathways but also common functional constraints limiting the range of phenotypic variation to be explored. Comparing directions of intrapopulation variance to the course of interpopulation evolution can thus be of help to bridge several evolutionary levels and contribute to an integrated vision of the phenotypic evolution.