Evolving Human Brains: Paleoneurology and the Fate of Middle Pleistocene

In the evolutionary radiation of the human genus, we have observed changes in both brain size and proportions. Some of these morphological differences are thought to be associated with functional variations, in physiological or cognitive aspects, while some others are the secondary results of cortical or cranial structural constraints. Most archaic human species, like Homo erectus and H. heidelbergensis, display larger brains when compared with earlier hominids, but specializations in their cortical proportions, if there are any, are difficult to recognize. In contrast, after or during Middle Pleistocene, more derived species like H. sapiens and H. neanderthalensis show changes in overall brain size but also in specific cerebral regions. Functions associated with body cognition, visuospatial integration, tool use, language, and social structure may be involved in these paleoneurological changes. Nonetheless, a proper evaluation of cognitive differences must take into account not only the cerebral components, but also the associated mechanisms underlying technological extension. Brain-body prosthetic capacity can have represented, indeed, a crucial adaptation to become obligatory tool users. These processes involve both genetic and environmental effects, and they are probably influent at phylogenetic (species) and historical (populations) level, bridging biological and cultural factors through epigenetic feedbacks that are still poorly known and scarcely investigated.