Design features for language and stone toolmaking (not tool use) involve similar if not homologous cognitive processes. Both are arbitrary transformations of internal symbolization, whereas non-human tool using is mostly an iconic transformation. The major discontinuity between humans and non-humans (chimpanzees) is language. The presence of stone tools made to standardized patterns suggests communicative and social control skills that involved language.

Despite the ontogenetic allometric size effects that explain much of phyletic variation in brain components, the residuals of some structures indicates that mosaic brain evolution was an important factor in hominid evolution, and that reorganization of the hominid brain may have occurred as early as 3+ MY. Finlay et al.'s allometric technique masks residual variation around allometric trends, and the patterns of residuals relevant to species-specific departures from strict allometric trends.

If POT (parieto-occipital-temporal junction) reorganization came earlier in australopithecines than in Homo, it is likely that the selective pressures were different, and not necessarily directed toward language. The brain endocast evidence for the POT in A. afarensis is actually better than it is for early Homo.

Data do exist to support the fact that the corpus callosum is relatively larger in women than in men. The corpus callosum is an integral part of the brain, and contrary to Fitch & Denenberg's examples of “pseudostatistics,” is not an extrinsic structure when determining its relative size.

Given the primate propensity to make noise, it is unclear why a manual gestural stage would have been necessary in the development of either language or right-handedness. Cortical asymmetries are present in australopithecines but become clearly human-like with the appearance of Homo about two million years ago, including Broca's cap regions. Stone tool-making is still our only empirical entry into past cognitive processes.