Genetic explanations 3: neurobehavioural explanations

These hypotheses propose brain and behavioural evolution as the driver of the adaptations that are now leading to CVD and DM2. Of these, the behavioural switch, also known as the soldier-to-diplomat, hypothesis is best developed. The concept is that as humans moved from hunter-gatherer to settled agricultural lives, complex changes occurred to support this lifestyle, e.g. reduced aggression, more resources to nurture fewer children, and preferential use of glucose by the brain rather than by muscle. Insulin resistance is seen as a secondary—once beneficial—adaptation underlying this change. This hypothesis implies insulin resistance is valuable and it also provides an explanation for South Asians’ reduced muscle mass. Similar ideas have been proposed on longer evolutionary timescales, e.g. the aggression control hypothesis. At present the evidence from these hypotheses does not explain South Asians’ particular susceptibility to CVD and DM2. The hypotheses do, valuably, point to the brain’s central role in glucose metabolism.