Stag beetles show a great intraspecific variation. The morphological variation of a species at a single location is a reflection of the species developmental plasticity (DP) and that across locations is a measure for the species adaptive plasticity (AP). Variations of external morphology (developmentally highly variable) and reproductive organ (developmentally highly stable) were studied in each of 514 locations comprising 187 species to determine intralocational, interlocational, and interspecific variability. Dealing with naturally occurring variation, extra attention was paid to the normality of each data set and the validity of partitioning each variation component. With this, the comparative quantification of DP and AP and its presentation as broad-sense heritability were made possible. The results indicate that intraspecific evolution begins with the diversification in genitalia morphology through selection on individual phenotypes as the traditional theory dictates while DP of external morphology sustains the morphological robustness of species. More significantly, there was a highly significant difference in DP of external morphology among species and the interspecific, broad-sense heritability of DP in body and mandible length was very high, indicating that DP is firmly a genetic trait on its own. Furthermore, DP (of body length) influences the species geographic range (GR) more significantly than the species mean or other measures. DP in external morphology and GR being a highly heritable emergent trait and an emergent property, respectively, at the species level, these findings suggest that DP plays a significant role in interspecific evolution through species selection rather than selection on individual phenotypes.