Wednesday, February 9, 2011

"Peeled truffles and seasoned mushrooms": how are the sins of the fathers visited on their sons?

One of the big sources of dissension among people trying to place human behavior and social organization in the context of biological evolution is understanding the nature of heredity.  It is only hereditary causes that are involved in evolution (and for the purposes of this post, that means genes) and hence play a role in the nature of organisms over the long haul.  What you are depends on your environment, but your reactions to that are constrained by the patrimony built up over 4+ billion years of heritable ancestry.

There are countless examples of casual views of what makes us what we are.  One of us (Ken) has been reading the satires written by the Roman author Juvenal, writing about 125 AD.  Satire 14 seemed relevant to these ideas.  Here's one translation.

Satire 14 is called "The influence of vicious parents" in at least one translation (though it's "No teaching like that of example" in another).  In any case, Juvenal notes the strong influence of parents.  Some children learn from their "wastrel father... to enjoy such things as peeled truffles and seasoned mushrooms, and warblers steeped til they drown in the mushrooms' sauce."

"So Nature ordains," writes Juvenal, that "no evil example corrupts us so soon and so rapidly as one that has been set at home, since it comes into the mind on high authority." [this quote from a different translation]   Juvenal is being cynically satirical about bad, selfish, or debauched human behavior, but his point is cogent: to a great extent we are what we pick up at home.

The point here, with respect to modern genetics, and MT, is that if one has a belief that this or that trait is inherited in the genetic sense, one can make up stories of how the trait got that way, by virtue of a long history of natural selection.  But what evidence do we need before we should be taken seriously in such arguments of inherency?

The essential evidence must include that there are family resemblances.  Factors like recessiveness can obscure patterns, but so can what are called 'incomplete penetrance' or 'phenocopies' or 'sporadic' instances of a trait.  This means that even if there is a gene 'for' a trait--that is, whose variation confers the trait on its inheritor--the trait may not always be present, or, it can arise for other reasons.  Family environment is another factor that influences presence/absence of a trait.

Rigorous genetic inference should have to show that traits are not just familial, but obey Mendel's laws of inheritance.  However, the problem is that such patterns are almost impossible to prove, because there are so many possible causal factors ('parameters' in the statistical tests of inheritance patterns), that almost any trait, or any hypothesis, can be given support.  This is made all the more complicated by the obvious and undoubted fact that many if not the vast majority of genetic effects are context-dependent, in that they are affected by the environment.  And environment begins at home.

The difficulty of showing that a trait that aggregates in families actually 'segregates' as Mendel's laws would have it, has led to a general abandonment of rigorous segregation analysis, replaced by the assumption that traits simply must be importantly genetic and all we need to do is scan the whole genome to find the responsible genes.  How much greed, vice, or seasoned mushrooms is needed to show that the child is the likeness and image of the parent?  See all our previous posts on GWAS if you want to know what the issues are (and what we think of them, whether you agree with us or not!).

In this very sloppy epistemological environment, that is, we face fluid and largely unconstrained criteria for making inferences about what is genetic and what isn't, and how something that you assume 'must be' genetic can be explained by some sort of adaptive scenario that you can invent.  This makes assumption into truth in a rather untestable way.  And when evidence is gathered, there are so many ways to interpret it that it is almost always possible to find one that fits your prior expectations.

Each of us is, to a great extent, what we are.  Clearly everything about us has some genetic under-pinnings, or we would not so clearly resemble our parents to an obvious extent.  But just as clearly, much of what we are comes from our surroundings.  In that sense, it is not inherent in us.

Social politics is complex but there are many reasons why it is convenient to view the sins of the sons as having been visited on them by their fathers. But if "young people readily copy most of our vices," as Juvenal wrote, selfishness and greed and other sins may reflect the nature of society as much as they do the nature of our genes.  Sorting this out is a major challenge, because there are so many social consequences when those in power use convenient assumptions to manipulate others to their own advantage.  Science is built on assumptions, but assumptions are not science.

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