Doberman Pinscher pups 

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 we acquired 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 learned that most Dobermans had had their tails bobbed for many generations, I wondered why the tails, after so many generations of bobbing, 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, I took several biology courses. 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. At first I did not want to let go of this cherished opinion of mine. I had always thought of myself as progressive, modern, scientific; I did not believe in creationism. I thought 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 cause their pups’ tails to be any shorter that I 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 did at birth. Chopping off a dog’s tail doesn’t change the genes it carries in the sex cells that govern how long the pups’ tails will be. Under Lamarckism, by contrast, an animal’s genes are pictured as changing because the animal’s body has been injured or stressed in some way. Lamarckism says a chimp, for instance, will pass genes for larger arm muscles on to its young if the parent chimp has had to use its arm muscles a lot.

But Darwinian evolution gives us what we now see as a far more useful picture. In nature, individuals within a species that are no longer well camouflaged in the changing flora of their environment, for example, become easy prey for predators and so they never survive long enough to have babies of their own. Or ones that are unable to adapt to a cooling climate die young or reproduce less efficiently, while their stronger, smarter, or better camouflaged cousins flourish.

Then, over generations, the 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, the gene pool changes. Eventually, as a consequence, there will be many more individuals with the shorter tail that has now become a normal 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 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 became just 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.

The question arises: how would the Bayesian way of choosing between the Lamarckian and Darwinian models of evolution or of reshaping one’s views on the mentally challenged compare with the empiricist way or the rationalist way of dealing with these same problems?

The chief danger of empiricism that Bayesians try to avoid is the insidious slip into dogmatism. Many times in the history of science, empiricist-minded scientists have worked out and checked a theory so thoroughly that they have slipped into thinking that they have found an unshakeable truth. For example, physicists in the late 1800s were in general agreement that there was little left to do in physics. They believed that Newton and Maxwell, between them, had articulated all the truths of all levels of the physical world, from the atomic to the cosmic. Einstein’s theory of relativity changed all of that. For many physicists of the old school, relativity was a very rude shock.

                                                                      

                                                             James Clerk Maxwell

Today, physics is in a constant state of upheaval. A few physicists still show a predilection for dogma, or we could say a longing for certainty, but most modern physicists are tentative and cautious. They’ve been let down so many times in the last hundred years by theories that once had seemed so promising, but that later were shown by experiment to be flawed, that most physicists have become permanently leery of any colleague who claims to have “the truth.”

It is regrettable that a similar caution has not caught hold of a few more of the physicists’ fellow scientists, especially the biologists. Darwinian evolution is indeed a powerful and impressive theory. It explains virtually all aspects of the living world that we currently know about. But it is still only a theory, which means that, like all theories, it should be viewed as tentative, not final or irrevocable. It just happens currently to have vastly more evidence to support it than do any of its competitors.

The larger point for our purposes here, however, is that Bayesians never endorse any one model as the last word on anything, and they never throw out any of the old models or theories entirely. Even those that are clearly wrong have things to teach us, and of the ones that are currently working well, we have to say that, simply, they are currently working well. There are no final answers and no final versions of the truth in any model of reality for a Bayesian. The theory of evolution is only currently working well.