Brain Science Reveals that Trust is Our “Default State”
Some of you might believe that the natural state of mankind is “warre of every man against every man—Bellum omnium contra omnes” (Hobbes, Leviathan, 1651). Here is some hard evidence to the contrary:
The most comprehensive and up-to-date lay book on the science of behavior is Stanford neuro-endocrinologist Robert Sapolsky’s Behave: The Biology of Humans at Our Best and Worst (2017). The book is a encyclopedic compendium of behavioral science, written with folksy, down-home idiom. Here he lays out evidence that the fundamental “default” of human social behavior is trust, and that the brain structure, the amygdala, is involved in applying justice when needed.
The amygdala . . . plays a logical role in social and emotional decision making. In the Ultimatum Game, an economic game involving two players, the first makes an offer as to how to divide a pot of money, which the other player either accepts or rejects. If the latter, neither gets anything. Research shows that rejecting an offer is an emotional decision, triggered by anger at a lousy offer and the desire to punish. The more the amygdala activation in the second player after an offer, the more likely the rejection. People with damaged amygdalae are atypically generous in the Ultimatum Game and don’t increase rejection rates if they start receiving unfair offers. . . . [T]hese findings suggest that the amygdala injects implicit distrust and vigilance into social decision making. All thanks to learning. . . . “The generosity in the trust game of our BLA [amygdala]-damaged subjects might be considered pathological altruism, in the sense that inborn altruistic behaviors [my italics] have not, due to BLA damage, been un-learned through negative social experience.” In other words, the default state is to trust, and what the amygdala does is learn vigilance and distrust.
Dr. Sapolsky goes on to explain that, among the inputs to the amygdala is a region in the prefrontal cortex called the “insula,” which is activated when one tastes or smells something disgusting. This area is also activated by morally objectionable behavior: “Someone does something lousy and selfish to you in a game, and the extent of insular and amygdaloid activation predicts how much outrage you feel 
and how much revenge you take. This is all about sociality—the insula and amygdala don’t activate if it’s a computer that has stabbed you in the back.” So the amygdala, the brain structure concerned with anxiety, fear and rage, is intimately responsive to moral sensibilities.
In other primates, the amygdala plays the same general role, but is hugely less developed. The”default” human social attitude of trust could only have evolved over long periods of time in response to a social structure of morality and justice. I have long theorized in the blog (and book) that morality-and-justice is the fundamental human adaptation. Faced with extinction, six million years ago, selection for the fitness of individuals in apes shifted to the selection of productive relationships in humans—the more moral and just the relationship, the more productive it is.
In evolutionary terms, a social system of morality and justice is defined as “the most productively fertile structure possible.”
While I’m at it, here is a fascinating insight into our socially-mediated emotional responses to the pursuit of pleasure. Dr. Sapolsky describes,
. . .the amygdala isn’t about the pleasure of experiencing pleasure. It’s about the uncertain, unsettled yearning for a potential pleasure, the anxiety and fear and anger that the reward may be smaller than anticipated, or may not even happen. It’s about how many of our pleasures and our pursuits of them contain a corrosive vein of disease.
