Against the Grain: A Deep History of the Earliest States

by James C. Scott

More diagnostic than the overall reduction in brain size are the areas of the brain that seem to be disproportionately affected. In the case of dogs, sheep, and pigs, the part of the brain most affected is the limbic system (hippocampus, hypothalamus, pituitary, and amygdala), which is responsible for activating hormones and nervous-system reactions to threats and external stimuli. The shrinkage of the limbic system is associated with raising the threshold that would trigger aggression, flight, and fear. In turn, this helps explain the diagnostic characteristics of virtually all domesticated species: namely the general reduction in emotional reactivity. Such emotional dampening can be seen as a condition for life in the crowded domus and under human supervision, where the instant reaction to predator and prey are no longer powerful pressures of natural selection. With physical protection and nutrition more secure, the domesticated animal can be less intently alert to its immediate surroundings than its cousins in the wild.