Incomplete Penetrance and the Complexity of Belief

[I stumbled across this article by "Mike Gene" the author of The Design Matrix and thought it might be a good conversation piece.]

In genetics, there is a concept known as penetrance. This concept is typically most relevant with dominant mutations that cause disease and the idea here is that not all genotypes elicit their expected phenotypes. For example, consider the phenonmena of polydactyly in humans. This is where an individual has extra fingers and/or toes. Since this trait is caused by a dominant mutation, you would expect that anyone with the dominant allele would have this trait. Yet this is not always true. The concept of penetrance comes into play when we estimate how many with a particular genotype express the trait. For example, if 90 out of 100 people who are heterozygous have the trait, we’d say the trait is 90% penetrant.

So why is it that many traits show less than 100% penetrance? Two factors come into play – the genetic background and the environment. Whether or not a particular allele at a specific locus is expressed can be a function of the expression of other alleles at other loci. Thus, without the right genetic context, a particular genotype may not be expressed. As for environment, it is well known that it can work in conjunction with a genotype to determine whether a particular phenotype is seen. This means that certain traits will be expressed only in the right environmental context.

I mention all of this simply because it makes for a nice metaphor in understanding how humans believe. Many people share the naïve notion that a powerful argument for X should elicit belief X. If someone is thus presented with argument X, yet fails to adopt belief X, that person is then viewed negatively (i.e., they are stupid, deluded, or dishonest).

But let’s assume the argument is the allele (genotype) and the belief is the trait (phenotype). Whether the argument leads to belief depends on the context of background beliefs and experience that already exist (akin to genetic background) and the social setting (the environment). The argument for X may fail to elicit belief X simply because of incomplete penetrance. In such cases, the power of the argument for X is dependent on the context of other beliefs and knowledge and the way belief X plays out in social reality.

Such incomplete penetrance is not stupidity, delusion, or dishonesty. It exists as a function of the Complexity of Belief. We not only believe differently, but we think differently. Thus, an important lesson in life is to realize that other people are not extensions of your self.

Augustine: On The Trinity | 2

Since no one can love at all a thing of which he is wholly ignorant, we must carefully consider of what sort is the love of those who are studious, that is, of those who do not already know, but are still desiring to know any branch of learning...

...in all cases the love of a studious mind, that is, of one that wishes to know what it does not know, is not the love of that thing which it does not know, but of that which it knows; on account of which it wishes to know what it does not know. Or if it is so inquisitive as to be carried away, not for any other cause known to it, but by the mere love of knowing things unknown; then such an inquisitive person is, doubtless distinguishable from an ordinary student, yet does not, any more than he, love things he does not know; nay, on the contrary, he is more fitly said to hate things he knows not, of which he wishes that there should be none, in wishing to know everything. But lest any one should lay before us a more difficult question, by declaring that it is just as impossible for any one to hate what he does not know, as to love what he does not know, we will not gainsay the truth of this statement; but it must be understood that it is not the same thing to say he loves to know things unknown, as to say he loves things unknown. For it is possible that a man may love to know things unknown; but it is not possible that he should love things unknown. For the word to know is not placed there without meaning; since he who loves to know things unknown, does not love the unknown things themselves, but the knowing of them.