Modular brain

One of the main achievements in anatomy and morphometrics has been the introduction of the concepts of integration and modularity. Characters (and genes) are no longer interpreted as individual and independent units, but integrated into structural and functional systems. This does not mean that everything is integrated, and we should recognize that integration and modularity are based on both continuous and discontinuous hierarchies presenting many different degrees of relationship. There may be distinct combinations, and very different situations. Analyzing the structure of covariance of the endocranial base in modern humans, I suggested that local influences can be more relevant that general and long-range factors, in shaping the endocranial districts. An admixture of effects from brain, face, posture, muscles, physiology and biomechanics, makes local factors decisive to mould the specific endocranial areas. Similar results were obtained when analyzing the covariance patterns of the midsagittal brain morphology. Now Aida Gómez-Robles and colleagues have published a decisive analysis: the whole brain in three dimensions. The integration among brain parts is modest, and largely based on spatial proximity. Local factors are crucial in moulding the brain areas, at least in terms of their morphology and position. Initially one can be deceived if expecting to find a more integrated system. But at the same time such an independent organization suggests that local form changes can be analyzed considering the local context, the morphology being less contaminated by external (long-range) effects. Interpretations are easier if only local factors must be evaluated. This is something extremely relevant when dealing with evolutionary neuroanatomy, paleoneurology, and functional craniology. And then there is an issue on evolvability: the authors suggest that such limited integration can facilitate evolutionary changes.