Evolution built partisanship into our brains

A root of today’s political conflict is all in our head — in our brain actually. One cause of our partisan division stems from the signature duality of that remarkable organ and the way(s) the human brain developed over the millennia. We are at a potential evolutionary crossroads — a battle is raging in our brains between primordial circuits that inspire tribal responses and potential escalation in hostility, and a highly evolved cortex that is struggling to realize its birthright and find interconnectedness for a greater good. The growing trend in American society to reverse the natural evolutionary achievement of human brain development is a profound threat to what makes our species great.

Polarization, nativism, racism, — alarming words describing the state of American politics, which continues to exhibit distressing tendencies toward tribalism despite evidence that partisan policies undermine the general public’s health and interests. A glaring example is the current partisan divide over what is more dangerous to our well-being: 1000 deaths per day from an out of control virus, or sporadic vandalism and rock-throwing from fringe elements in crowds protesting racial injustice. How do these intransigent, partisan belief systems circumnavigate reason? How do our are brains let this happen to us?

In part, humans behave this way because our brain evolved to make us a herding species. Just as it is with other primates, group affiliation — the forming of tribes and clans — is an essential element of human culture. Because we lack many of the physical tools that other species need to survive in the wild, we form groups for among other things, hunting, protection, and home-building. Humans innately appreciate that there is safety in numbers and comfort in joining a group and following a strong leader.

Our herding tendency is based on millions of years of brain evolution, and two circuits in this organ are principally responsible. One helps us respond to the unfamiliar, while the other makes us feel that we are right. First, when encountering something unfamiliar, most mammals’ brains have a self-protection reaction. Evolution built this survival mechanism into specific brain regions, a circuit that runs through the amygdala, hippocampus, and the cingulate cortex. In the wild, survival depends on being vigilant and these structures work together to initiate a “call to arms” signal. In humans, unfamiliar stimuli activate this same circuit and initiate an internal signal that leads to feeling uncomfortable. While the human circuit is less extreme in its response, it sets a tone in the brain that makes unfamiliarity a potential source of anxiety and makes accommodation to unfamiliarity a struggle, because the innate response is wariness and suspicion.

In contrast to other animals, humans are particularly sensitive to physical appearances and to faces. The human brain is especially adapted to recognizing faces because survival has required distinguishing familiar and friendly, from the unfamiliar and potentially threatening. Faces that suggest a person is from another clan or tribe may seem threatening and tend to activate the “call to arms” circuit. Seeking comfort from familiarity and protection from strange people undergirds the human tendency for group affiliation and identity. Showing a face that looks alien is often used as a strong implicit message to manipulate fear in political ads and in news reports.

The second part of our tribal brain is the reward circuit. This is a brain wiring diagram that is turned on by things that feel good, make us feel strong and make us want more of the same. Running through the brainstem, striatum, and prefrontal cortex, this circuit is also critical for learning new things and for adopting beliefs and ideas that make us feel good, that make us feel right. We repeat behaviors that are rewarding, so joining a cheering crowd and feeling that your group is better and stronger activates this reward circuit and makes us want more of that experience. Experiences and people that feel alien deactivate the reward circuit, invoke feelings of repulsion, and teach us to avoid those encounters.

The human brain shares these basic circuits, but we also have something that other animals don’t — a highly developed neocortex, epitomized by a region called the prefrontal cortex. This part of the brain is responsible for language, abstract thought, planning for the future, and intellectual and technical achievement. This uniquely human development makes it possible for us to resist strong urges from the tribal circuits because it also allows us to imagine that the unfamiliar may not be dangerous, that “clouds may have silver linings”. Successful societies have capitalized on prefrontal cortical evolution by seeking to create institutions, laws, and governments that offer alternatives to the innate brain responses and that reward the pursuit of goals not favored by one group or another but that work for the interests of the larger society.

In essence, all of these brain systems are about the survival of our species. But as history and the environment have changed, overriding instinctual pressures has become increasingly critical. Our neocortex evolved to enable us to learn and utilize new and advantageous strategies for group affiliation and reward not based on tribal instincts. The growing partisan divide in America challenges this natural evolution and is a profound threat to what makes our species great. We are at a dangerous crossroads in this evolutionary battle and our neocortex is crying out for help. The solution to times like this has been the same throughout human history: an auxiliary prefrontal cortex is needed in the form of leadership that encourages community, interconnectedness, and pursuit of a common good.

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