A new paper by Melchionna and colleagues provides new insights on the never-ending issue of the evolution of human brain asymmetries. The study supplies a comprehensive shape analysis of endocasts from many hominoid taxa, including fossils. Differences that go beyond the allometric consequences of a larger brain can be detected in Homo sapiens, Homo heidelbergensis, and Homo neanderthalensis. The brain is asymmetric in its anatomy and functions and, after more than a century of debate, we still don’t know if our degree and scheme of asymmetry is due only to a larger cortex, or else if there are some specific evolutionary adaptations. Of course, a unique (all hominoids) trend is not necessarily expected, and each species can have had its own, independent and peculiar story. Indeed, we should not forget that there is a major limitation in paleoneurology: if things are not clear for living primates and living brains, little can be probably done with fossil species and gross endocranial moulds. The anatomical and statistical uncertainties are, at best, unquestionable. In this sense, there is still a major biological issue which is largely unresolved: we ignore the nature of the endocast asymmetries. White matter or grey matter? Are neurons, glia or blood involved? Skull- or brain-induced? It is a physiological or biomechanical issue? Unless we have clear evidence on these aspects, the information on “how much” and “where” a cast is asymmetric may be but a secondary information.
