I read and weep about the rage and division poisoning America right now, particularly on the eve of the most fiercely battled mid-term elections in my memory.

My worry is that all this anger and division, now being stoked by both political parties, is fomenting the recent violence we’re seeing – the bombs mailed to prominent Democrats, the slaughter in the Pittsburgh Tree of Life synagogue, the recent shootings of two black men – and we haven’t seen anything yet.
Infectious hate speech
Psychiatrist Richard Friedman, who recently wrote about the neuroscience of hate speech in the New York Times, said that ‘repeated exposure to hate speech can increase prejudice, as a series of Polish studies confirmed last year’ largely because it "normalizes what is usually socially condemned behavior."
He also quotes Susan Fiske, a Princeton psychologist, who has shown that distrust of an ‘out-group’ – someone not like you – is linked to a greater tendency toward anger and violence: people will nurture and act on their prejudices in the worst ways when these people are put under stress, pressured by peers or receive approval from authority figures to do so.
One of the most famous studies of the individual’s relation to the dynamics of groups in an authoritarian environment is the Stanford Prison Experiment carried out in 1971.
Stanford University psychologist Philip Zimbardo created a mock prison in which a group of middle-class young men, especially screened to be the most psychologically stable of all those who volunteered, were randomly assigned the roles of guards and prisoners, with Zimbardo assuming the role of prison supervisor.
The experiment quickly got out of hand. The ‘prisoners’ were given prisoner “uniforms,” referred to only by number, and made to follow arbitrary orders and punishments in order to mimic the dehumanizing aspects of prison.
The guards became more and more demanding and aggressive in creating and enforcing rules, finally subjecting the prisoners to degrading and even pornographic tasks, and the prisoner students accepted their humiliating treatment (even though they knew they could leave at any time during the experiment).
Zimbardo himself had gotten so drawn into his role of prison supervisor that it took an outsider — a student visiting the experiment — to alert him to how badly the situation had deteriorated. The truthsayer eventually became Zimbardo’s wife.
This pivotal study has been cited in psychology classes ever since as proof positive that groups have an automatic Lord-of-the-Flies effect, causing people to shed their moral judgment, even their humanity, when subjected to a strong authority figure.
Another take on the experiment
In 2002, two British social psychologists, Alexander Haslam at Exeter and Stephen Reicher at the University of St. Andrews in Scotland, wished to revisit these ideas by recreating the Stanford University experiment. Funded and filmed by the British Broadcasting Company (and eventually shown on TV as The Experiment), the two psychologists created an elaborate prison, and again randomly assigned a group of men the roles of either prisoners or guards.
Over eight days, the experimenters witnessed stunning developments. Although the prisoners were initially demoralized, the group dynamics shifted over time.
As the prisoners began to develop a sense of shared identity, they began to function effectively as a group and also enjoyed improved morale and mental well-being.
This shared identity also led to improved health profiles; the prisoners experienced a lowering of cortisol – the hormone pumped by the body in times of stress.
As the experiment carried on, the prisoners became stronger, happier, and empowered. The guards, on the other hand, who had not bonded as a group, became increasingly dispirited and powerless, exhibiting high levels of cortisol. Eventually the prisoners staged a breakout and the authority of the guards collapsed.
Even as a beleaguered group, the BBC prisoners remained robustly immune to treatment by the guards — so long as they could connect with others in the same boat. In fact, the more they were oppressed as a group, the stronger they became.
Social psychologist Willem Doise suggests that one way that we can come together and overcome our differences is by “cross-cutting categories” — attaching ourselves to more than one group.
That practice not only reduces the prejudice against “out” groups but also tends to stop people from making comparisons. It reduces our need to relate to just a single factor — religion, sexual identity, or politics or even socio-economic background — in order to feel that we belong.
As psychologists put it, people who belong to many groups create a “superordinate” identity for themselves, which in itself has been shown to reduce prejudice and fear.
In a study of religious diversity, American Grace, Robert Putnam discovered that America is becoming increasingly tolerant of religious diversity and far more disposed to having family members marry outside their own church.  Contact and familiarity between dissimilar groups did in fact breed acceptance, even if ethnic or political diversity does not, at the moment.
That suggests that acceptance and cooperation can be cultivated – and restored.
The same is true of our political alliances as Americans.
Want to stop creating hate and division in your town and neighborhood? It’s very simple. Create a bowling league, or a book group and invite Democrats and Republicans. Or start a Neighborhood Watch and invite both sides.
Like overlapping molecules, we can learn to connect again and reclaim our natural way of being by creating a larger, all-embracing identity, a bigger definition of who “we” are. The more groups you can label as part of yourself, the more people you will embrace.