Chapter 6.             Part B 

Now at this point in the discussion, opponents of Bayesianism begin to marshall their forces. These critics of Bayesianism give several varied reasons for continuing to disagree with the Bayesian model, but I want to deal with just two, two of the most telling, one for practical, evidence-based reasons and the other, in the next chapter, for purely theoretical reasons.

In the first place, say the critics, Bayesianism simply can’t be an accurate model of how human beings think because humans violate Bayesian principles of rationality every day. Every day, we commit acts that are at odds with what both reasoning and experience have shown us is rational. Some societies still execute criminals. Men continue to bully and exploit women. Adults spank children. We do these things even when both formal research everyday experience indicate that such behavior is counter-productive.

We fear people who look different than we do on no other grounds than that they look different than we do. We shun them even when we have evidence which shows that there are many trustworthy individuals in that other group and many untrustworthy ones in the group of people who look like us.

Over and over, we act in ways that are illogical by Bayesian standards. We stake the best of our human and material resources on ways of behaving that both reasoning and evidence say are not likely to work. Can Bayesianism account for these glaring bits of evidence that are inconsistent with its model of human thinking?

The answer to this critique is disturbing. The problem is not that the Bayesian model doesn't work as an explanation of human behavior and thinking. The problem is rather that the Bayesian model of human thinking and the behaviors driven by that thinking works too well. The irrational behaviors which individual humans engage in are not proof of Bayesianism's inadequacy, but rather of how it applies not only to the thinking, learning, and behavior of individuals, but sometimes moves up a level to the thinking, learning, and behavior of whole communities and even whole nations.

Societies evolve and change because, in every society, there are some people who are naturally curious. These curious people constantly imagine and test new ideas and new ways of doing things – getting food, raising kids, fighting off invaders, healing the sick – any of the things that the society has to do in order to carry on. It is also often the case that other sub-groups in society view any new idea or way of doing things as threatening to their most deeply held beliefs. If the adherents of the new idea keep demonstrating that their idea works, and thus, that the more intransigent group’s old ways are obsolete, and if that intransigent sub-group steadfastly refuses to re-write its belief system, then the larger society will, usually, marginalize the less effectual members and their system of ideas. In this way, a society mirrors what an individual does when he/she finds a better way of growing onions or teaching kids or easing Grandpa's arthritic pain. We adapt - as individuals, but more profoundly, as societies - to new lands and markets and to cars, televisions, vaccinations, email, etc. Farmers and cooks and teachers who cling to methods that don't work very well are simply passed by, eventually even by their own grandchildren.  

  

But then there are the more disturbing cases, the ones that make me say "usually" above. Sometimes large minorities or even majorities of citizens hang on to obsolete concepts and ways. 

The Bayesian model of human thinking works well, most of the time, to explain how individuals form and evolve their basic idea systems. Most of the time, it also can explain how a whole community, tribe, or nation can grow and change its sets of nation-wide beliefs, thinking styles, and customs and practices. But can it account for the times when majorities in the community do not embrace new ways even when the Bayesian calculations and the evidence show the ideas to be sound? In short, can the Bayesian model explain the darker sides of tribalism?

          

                                          Nazi party rallies: Tribalism at its worst 

  

As we saw in our last chapter, for the most part, individuals become willing to drop a set of ideas that seem to be losing their effectiveness when they also encounter a new set of ideas that looks more promising. They embrace the new ideas that perform well, i.e. that guide the individual well, through the hazards in real life. Similarly, at the tribal level, whole societies usually drop paradigms, and the ways of thinking and living based on those paradigms, when the citizens keep seeing that the old ideas are no longer working and that there is a set of new ideas that is getting better results. Sometimes, on the level of changes that sweep across a whole society, this mechanism even means societies marginalize or ostracize sub-cultures that refuse to let go of the old ways.  

The point is that when a new sub-culture with new beliefs and ways keeps getting good results, and the old sub-culture keeps proving ineffectual by comparison, the majority usually do make the switch to the new way …of chipping flint, or growing corn, or spearing fish, or making arrows, or weaving cloth, or building ships, or forging gun barrels, or dispersing capital to the enterprises with the best growth potential, or connecting a computer to the internet.