Parsimony has become very popular with scientists and philosophers. The idea is that the simplest explanation for any phenomenon – the one that includes the fewest possible number of causal factors – is the best explanation. This principle was used by William of Occam in logical arguments and has been popularly called Occam’s Razor. It is often applied to situations where one must choose between alternate theories, one of which includes a fewer number of causative factors or a simpler mechanism than the other.
“Entities must not be multiplied beyond necessity.”
- William of Occam
“We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances.”
“…the simplest hypothesis proposed as an explanation of phenomena is more likely to be the true one than is any other available hypothesis, that its predictions are more likely to be true than those of any other available hypothesis, and that it is an ultimate a priori epistemic principle that simplicity is evidence for truth.”
The idea certainly seems reasonable, but is it correct? It might be for most physical theories, but it’s quite wrong when applied to biology. There are in fact no simple phenomena in biology, and simple hypotheses simply fail on a regular basis. Biology works according to its own principles and laws, which are not the same as the logical constructions of the human mind. Nor are these laws easily reduced to the laws of physics. Simplicity might be evidence for truth in physics; it almost never is in biology. Here are a couple of examples:
Which hypothesis is more likely to be true?
- In a biochemical reaction where A is converted to B, an excess concentration of B inhibits the reaction.
- The same as 1, AND an excess concentration of A stimulates the reaction.
- The same as 2, AND an excess concentration of A stimulates another reaction C to D, and D also stimulates the reaction.
- The same as 3, and a couple more redundant stimulatory and inhibitory processes.
Note that 1 is sufficient to regulate the amount of A and B. It is the simplest solution. But it is almost never what actually happens. The correct answer is usually 4. One example is the control of the synthesis of deoxyribose trinucleotides (used in DNA replication).
Here is another one. We know that coloration in plants and animals is usually of some evolutionary benefit or purpose. Which hypothesis is likely to be true for fish living in the deepest ocean where no light exists?
- They should be devoid of color, since there is no possibility of there being any selective advantage for color where there is no light. Simple and logical
- Such fish should exhibit an enormous variety of brilliant and beautiful colors. Illogical, crazy.
Yes, the second one is correct. Fish living in the deepest part of the ocean have amazing colors – brilliant yellow, blue and orange patches on their scales that are never seen since all the fish and other creatures in this environment are blind. The fish have such amazing colors because in that environment, colors are irrelevant and cannot be harmful (by attracting predators, for example). They are the result of random mutations in pigment genes (carried over from their ancestors) that produce a phenotype with no detrimental effect on the survival of the individual, and are therefore never selected against.
Welcome to Biology.
There is a popular belief that phenomena have a single, simple explanation, and that once the best cause of anything is identified, all other potential causes can be ruled out. Like the principle of parsimony that underlies Occam’s razor and the other quotes above, this certainly does not work in biology. Whether at the organismal level or at the level of biochemistry, many different causes can produce the same effect. And one cause can produce a myriad of effects. This is why biological reality is so complex and so hard to capture in mathematical terms. It is true for metabolic pathways, for gene regulation, for animal behavior and for evolutionary biology.
In the next post I will discuss the implications of the failure of parsimony and simplicity in biology for theology. Comments from readers who might have a view on this issue are especially welcome here.