Craniodental robusticity in Paranthropus has been interpreted as evidence that species in this genus share an adaptationAdaptation to a diet of hard foods. However, recent research on craniodental morphologyMorphology, microwearMicrowear, biomechanicsBiomechanics, and stable isotopes has suggested that substantial variationVariation exists within Paranthropus, both in terms of the ecological niches occupied by the species and the inferred amount of consumed hard and compliant foods. Rather than pointing to a common adaptive suite, these studies suggested that the species were adaptively distinct from each other. However, current approaches to understanding cranio-mandibular morphology do not present a clear picture of how these species-specific adaptationsAdaptation differ. It is also unclear whether all aspects of morphology that have been attributed to adaptationAdaptation are indeed adaptive, rather than the products of non-adaptive processes. This study examines variationVariation in fossil specimens assigned to the three Paranthropus species (n = 39) using an approach that tests for adaptive divergence in morphologyMorphology against a null hypothesis of random change (i.e., drift). Extant species (Homo sapiens, Gorilla gorilla, PanPan troglodytes; n = 293) act as analogues for within species variance/covariance (V/CV) in the fossil taxa. Results reveal a high magnitude of variationVariation within and between species across mandibular/cranial regions, especially when Paranthropus robustus individuals from DrimolenDrimolen are included. Neutrality tests detect adaptive divergence between P. robustus and Paranthropus boisei and Australopithecus africanusAustralopithecusafricanus, but not between Paranthropus aethiopicus and P. boisei. Reconstructed selection vectors indicate that directional selection has driven size related changes in mandibular and tooth dimensions, as well as in the cranium, resulting in a range of morphological responses including considerable evidence for correlated selection. Additional studies are needed to further investigate the nature of adaptive and non-adaptive divergence in these fossil hominins.