Chapter 5       Bayesianism: How It Works

Part A

                        Thomas Bayes 

  The best answer to the problem of what human minds and human knowing are is that we are really all Bayesians. On Bayesianism, I can build a universal moral system. So what is Bayesianism? 

   Thomas Bayes' theory of how humans form tentative beliefs and gradually turn those beliefs into concepts has been given several mathematical formulations, but in essence it says a fairly simple thing. You tend to become more convinced of the truth of a theory or model of reality the more that you keep encountering bits of evidence which, first, support the theory and, second, can't be explained by any of the competing models of reality that your mind already holds. (A fairly accessible explanation of Bayes Theory is on the Cornell U. Math department website.) (1.) 

   But under the Bayesianism view, we never claim to know anything for certain. We simply hold some beliefs that we consider very highly probable, and we use them as we make decisions in our lives. In addition, we accept as given that all beliefs, at every level of generality, need constant review and updating, even the ones that seem for long periods to be working well at guiding us to handle real life. 

     

   The more that a new theory enables a mind to establish coherence within its whole conceptual system and all its sets of sense-data memories, the more reasonable the theory seems. If the evidence favoring the theory mounts, and its degree of consistency with the rest of the beliefs and memories in the mind also grows, then finally, in a leap of understanding, the mind promotes the theory up to the status of a concept and incorporates the new concept into its total stock of thinking machinery. 

    At the same time, the mind nearly always has to demote to “inactive” status some formerly held beliefs and concepts which are not commensurable with the new concept and so are judged to be less efficient in enabling the mind to organize and use its total stock of memories. This is especially true of all mental activities involved in the kinds of thinking that are now being covered by the new model or theory. For example, if you absorb and accept a new theory about how your immune system works, that idea will then oversee every health-related decision that you make.  

    In life, examples of the workings of Bayesianism can be seen all of the time. All we have to do is look closely at how we and the people around us “make up our minds”.

    When I was in junior high school, I used to be bused, in June every year, along with the other students of my junior high school, to the all-city track meet at a stadium in West Edmonton. Student athletes from all of the big junior high schools in the city came to compete in the biggest track meet of the year. Its being held near the end of the school year, of course, added to the excitement of the day.

    A few of the athletes competing came from a special school that educated and cared for those kids that today would be called “mentally challenged”. In my grade nine year, three of my friends and I, on a patch of grass off to one side of the bleachers, did a mock cheer in which we shouted the name of this school in a short rhyming chant, acted like we were trying to do some chorus line kicks in step, crashed into each other and fell down. I should make clear that I did not get that cruel an attitude from my home. My parents would have been appalled. But fourteen year olds can be cruel.

    The problem was that one of the prettiest and smartest girls in grade nine at my school was up in the bleachers, watching field events in a lull between track events. She and two of her friends happened to catch our little routine. By the glares on their faces, I could see that they were not amused. Later that day I learned that though she had an older brother who had gone to our school, done very well academically, and scored amazing grades on the provincial final exams, she also had a younger brother who was a Down’s Syndrome child.

    I apologized lamely the next day at school, but I could see that I’d lost all chance with her. However, she did say one thing that stayed with me. She told me that if you form a bond with a mentally retarded person (“retarded” was still what we called them in those days), you will realize that you have made a friend whose loyalty, once won, is unchanging and unshakeable. Probably, the most loyal friend that you will ever have. And that realization will change you.

Francis Galton (originator of Eugenics) 

    It was the proverbial “thin edge of the wedge”. Earlier, I had absorbed some of the ideas of the pseudo-science called “Eugenics” from one of my friends at school, and I had concluded that there was nothing of value that these people could give to the community and a great deal that they would inevitably take out of the community. Anne made me begin to question those assumptions.

    Over years of seeing movies like “A Child Is Waiting” and “Charlie”, and of being exposed to awareness-raising campaigns by the families of the mentally challenged, I began to see them in a different light. Over the decades, they came to be called “mentally handicapped” and then “mentally challenged”, and the changing of the terminology did matter. It changed our thinking.

    I became a teacher, and then, in the middle of my career, I saw some mentally challenged kids integrated into the public school where I taught. I also saw what they could teach the rest of us, just by being themselves.

   Tracy was severely handicapped, in multiple ways, mentally and physically. Trish, on the other hand, was a reasonably bright girl who had huge rage issues. She beat up other girls. She stole. She skipped classes. She smoked pot behind the school. But when Tracy came to us, Trish proved in a few weeks to be the best with Tracy of any of the students in the school. Her attentiveness and gentleness were humbling to see. In Tracy, Trish found someone who needed her, and for Trish, it changed everything. As I watched them together one day, it changed me. Years of persuasion and experience, by gradual degrees, finally, really got to me. I saw a new order in the community in which I lived, a new view of inclusiveness that gave coherence to years of observations and memories.    

      Today, I believe they are just people. But it was only grudgingly at fourteen that I even began to consider re-examining my beliefs about the mentally challenged. At fourteen, I liked believing that my mind was made up on every issue. Only years of gradually growing awareness led me to change my view. A new thinking model, gradually, by accumulation of evidence, came to look more correct and useful to me than the old model. Then, in a kind of conversion experience, I switched models. Of course, by gradual degrees, through exposure to reasonable arguments and real experiences, I and a lot of other people have come a long way on this issue from what we were in 1964. Humans can change.

A Doberman Pinscher 

     

     In a more scientific example, I will also mention our Doberman Pinscher cross pup. Rex was basically a good dog, but he was a mutt, a Doberman cross that we obtained because one of my aunts could not keep him. People often remarked that he looked like a Doberman, but his tail was not bobbed. This got me curious. When I found out that Dobermans had almost all had their tails bobbed for many generations, I wondered why the tails after so many generations had not simply become shortened at birth. I asked a Biology teacher at my high school, but his answer only confused me. Actually, I don’t think he understood the crucial features of Darwinian evolution theory himself.

Jean-Batiste Lamarck 

    Once I got to university, several of the courses I took were in Biology. Gradually, at first, and then in a breakthrough of understanding, I came to realize that I had been thinking in terms of the model of evolution called “Lamarckism”. I did not, at first, want to let go of this cherished opinion of mine. I had thought of myself as progressive; I did not believe in creationism. I had thought that I knew how evolution worked and that I was using an accurate understanding of it in all of my thinking. It was only after I had read more and seen by experience that bobbing dogs’ tails did not make their pups’ tails get any shorter, that I, gradually at first, and then in a mental leap, came to a full understanding of Darwinian evolution. 

   Evolution for all species proceeds by the combined processes of genetic variation and natural selection. It doesn’t matter how often the anatomies of already existing members of a species are altered; if their gene pool doesn’t change, the next generation will, at birth, basically look pretty much like their parents. Chopping off a dog’s tail doesn’t change the genes that he or she carries in the sex cells that will govern how long her/his pups’ tails will be.

      In nature, of course, some individuals no longer being well camouflaged in their changing environment, and so being easy prey, or their being unable to adapt to a changing climate or food supply, etc. causes some individual members of the species to die young or to reproduce less efficiently, while their stronger, smarter, or better camouflaged cousins flourish. 

    Then, over generations, the actual gene pool of the local community of that species does change. It contains more genes for short, climbing legs or long running legs or short tails or long tails or whatever the local environment is now paying a premium for. Gradually, the anatomy of the average species member changes. If short-tailed members have been surviving better for the last sixty generations, and long-tailed members have been dying young, before they could reproduce, this changes the gene pool. Eventually, as a consequence, there will be many more individuals with the shorter tail which has now become a basic trait of the species.  

     Pondering Rex’s case helped me to absorb Darwinism. My understanding grew and then, one day, through a mental leap, I suddenly "got" the newer, better model. A model that I hadn’t understood suddenly became clear, and it gave a deeper coherence to all of my ideas and observations about living things. For me, Lamarckism then became an interesting footnote in the history of Science, sometimes still useful because it showed me one way in which my thinking, and that of others, could go wrong.

     Now how would the Bayesian way of choosing between the Lamarckian and Darwinian models of evolution, or of re-shaping one’s views on the mentally challenged, compare with the Empiricist and Rationalist ways of dealing with these same problems?

Notes 

1. http://www.math.cornell.edu/~mec/2008-                           2009/TianyiZheng/Bayes.html