Chapter 2: Asymmetry and the Brain

Asymmetry and the Brain provides an expert exploration into the enduring concept of hemispheric asymmetry and the functional division of the cerebral hemispheres. The inquiry begins with the paradox of why the human brain, an organ dedicated to connection, maintains a deeply separated, almost wholly divided structure, a feature that evolution has actively enhanced rather than unified. A major anatomical focus is the corpus callosum, the primary band of neural tissue connecting the halves, which paradoxically appears evolutionarily optimized to reduce, rather than maximize, connectivity relative to brain size, and whose function is strongly weighted toward inhibitory control—preventing the two sides from interfering with one another. Evidence from "split-brain" procedures further emphasized the extent to which each hemisphere can operate autonomously. The chapter details key structural differences, including the Yakovlevian torque, where the brain appears physically twisted: wider in the posterior left region and the anterior right region. Although language specialization is classically associated with left-hemisphere enlargement (like the planum temporale), the structural asymmetries are argued to be deeper than linguistic demands alone. The core explanation for this ancient evolutionary divide, present across vertebrates, lies in the adaptive need to maintain two fundamentally incompatible forms of attention simultaneously. The left hemisphere deploys narrow, focused attention for precise tasks such as feeding, manipulation, and categorization of known objects. Conversely, the right hemisphere maintains broad, vigilant, open attention essential for environmental awareness, predator detection, navigating social dynamics, bonding, and integrating new experience. In the human brain, this leads to two distinct ways of being in the world: the right hemisphere relates to the contextual, complex, unique, and embodied world of immediate experience, while the left hemisphere creates a "re-presented" world of static, fragmented, abstracted entities that facilitate prediction, control, and knowledge. This difference is amplified by the frontal lobe expansion, which grants humans the capacity for "necessary distance" from immediacy, enabling both high-level planning and self-control, as well as complex social functions like empathy and trust. The chapter concludes by noting that the type of attention brought to bear fundamentally alters the nature of the world that comes into being for us, shifting between the experience of interconnected "hownesses" and the fragmented analysis of discrete "whatnesses".