Since human language depends on a lateralized brain, one must study lateralization in living primates as compared to the fossil record in order to identify the point at which our hominid ancestors developed lateralization and, subsequently, the capacity for language. When examining the fossil endocast record, left-right cerebral hemispheric asymmetries are disputed to be found at the earliest approximately two million years ago, as evidenced by the fossil find KNM-ER 1470. In modern humans, gross brain organization is such that in overall appearance, there are cerebral asymmetries. Each hemisphere controls the opposite side of the body as well as certain functions. Typically the left hemisphere controls the production of language while the right hemisphere functions in tasks requiring spatial reasoning. The problem, however, is that language capabilities cannot be ascertained to derive from specific locations, despite that the neural mechanisms for language are typically located on one side of the brain or the other. Broca's Area, which can be seen as a small lump towards the front of the left side of the brain is typically associated with the production of language, and Wernike's Area, behind Broca's Area, is involved in the perception of sound. Other aspects of language cannot be associated with specific cranial locales. Because of the lack of a definitive location for these aspects of language, paleoneurologists can glean few definitive signs of language capacities from the fossil endocasts. Signs of Broca's Area are evident in KNM-ER 1470, also known as Homo rudolfensis, and later Homo speicies, such as H. ergaster.

This has lead to a difference in opinion between two major paleoneurologists, Dean Falk and Ralph Holloway. Falk believes that language capacity developed beginning with the Homo species, showing that KNM-ER 1470, dated to pre-1.8 million years, was the earliest hominid with a cortical sulcal pattern similar to that of modern humans in the region of Broca's Area. This area is a prerequisite to the ordered pattern of utterances that characterize modern human speech. Holloway, however, thinks that the capacity for language developed earlier, in the australopithecine species. He makes his observation based on what he perceives to be brain reorganization in australopithecines, an observation disputed by Falk.