Occam’s Razor is a very respectable rule of thumb. Basically it says that if you have to choose between two explanations that appear equally strong, choose the simplest. This may sound great and may work in some circles but IT IS NOT A GOOD RULE IN BIOLOGY and that includes neuroscience.
When people illustrate simple theories they often pick one of the foundation theories of science: relativity, quantum mechanics, the periodic table, plate tectonics, cell theory, evolution by natural selection, to name a few. These are very wide theories; they cover a lot of ground in their explanations. And on the surface they appear simple because the basic idea of each can more or less be expressed in a paragraph of text and/or a few equations. But that simplicity is an illusion. The details of any of these theories is very complex. A complete textbook on any of these theories will be huge and dense.
Evolution has resulted in organisms becoming more and more complex and varied. They started out as fairly simple single cells without internal compartments differing only slightly from one another. And how do they look now? There are still cells somewhat like the early cells but there is also a multitude of multi-celled plants, animals and fungi with very complex inner workings to their cells. They form communities of various sizes and numbers of different species. Evolution has complicated life – it is not a simplifying process. It is not simplifying and it is not simple to detail. Nothing seems straightforward in biology. Nothing seems really new and efficiently created from scratch for its purpose. Everything seems to be a re-working of some other sort of thing. Most things do more than one function.
So why does Occam’s razor seem so reasonable. We like the idea of simplicity and often equate it with perfection. Simple theories are easy to put into words, and therefore easy to communicate and understand. But none of this makes a theory more useful or more likely to represent some aspect of reality. We like our theories to fit with previous theories and even if they are complex, they appear simple because they are more familiar. In many cases, Occam’s razor seems valid because it is only used when it is obvious to the user which theory ‘should’ be chosen and an argument can be made that the favorite is the simpler. But when it comes to it, evidence always trumps simplicity. If it didn’t we could just dream up explanations from ‘first principles’ and not concern ourselves with anything but the beautiful simplicity of those explanations. Because we insist that good theories make accurate predictions, we cannot just look at how parsimonious a theory is. And in many people’s experience it has not been the simple theories that have made the useful predictions or stood up against the evidence.
Over the years I have grown very suspicious of simplicity. I do not see any reason why the universe should be a simple place. And one thing is for certain: the brain is not simple. We do not expect the brain to be simple. We expect it to be, as they say, ‘quirky’. We expect it to be elegant in a muddled way rather than a streamlined way. We expect it to be elegant the way the eye is. The eye appears to be built backwards so that the light has to past through a lot of cells feeding the optic nerve before the light can reach the light sensitive rods and cones. No engineer would do that. But those cells that are in front of the rods and cones form pathways so that the light reaching the sensitive cells can only come from the source and not from bounces inside the lens and eyeball. They eliminate fuzziness. And the light they obstruct is not required anyway as the sensitive rods can almost register single photons. It works and that is what matters. But there is no feeling of simplicity here, but there is no feeling of an inefficient kludge either, just a feeling of biological quirkiness. Biological quirkiness is what I expect we will find in the brain.