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Saturday, March 20, 2010

The Heritability Fraud

As I also discuss in detail in my upcoming book, another way that some "biological" psychiatrists twist the truth in order to justify their belief that certain behavioral problems are due to brain disorders is to try and make a case that they have their origins in genetics. Never mind that there is barely a legitimate neuroscientist alive that believes that any gene or any group of genes specifically codes for any complex behavior pattern in humans that varies widely from person to person.

Most of the "experts" who mislead the field by exaggerating genetic influences do concede that both genetic and enviromental factors play a part in creating behavioral syndromes. They have to, since the rate at which genetically identical twins both show the syndromes is almost never anywhere close to 100%. (Everyone seems to ignore a very important third factor: people's ability to anticipate upcoming events and their consequences and plan accordingly).

What they have done is to come up with a way to apportion these supposed causative factors into genetic and enviromental factors using a statistic called heritability.

Using studies of identical twins that were raised together versus those who were raised apart, they purport to estimate the "variance," or how much each of the various causative factors contributes to a certain disorder. The variance is expressed as a percentage of the total package. Variances are thusly assigned to genetic factors, "shared" environmental factors such as growing up in the same household, and "unshared" environmental factors.

In actuality, a determination of which parts of an environment are shared by siblings and which are unshared has a lot in common with finding water with a divining rod. Anyone foolish enough to think that both parents treat all of their children in anything remotely close to an identical manner must have no siblings and no more than one child.

The even more misleading tactic is to use the twin study statistic called heritability as a synonym for genetic. It is not. The statistic derived from twin studies is not a measure of genotype but of phenotype. Genotype refers to the actual sequence of molecule pairs in the DNA of which an individual’s genes are made. Phenotype, on the other hand, is the final result of the interaction between genes and the environment.

Most of the genes in a cell, even the ones that are at times active in a given type of cell such as a neuron, are in the “off position” most of the time. What turns them on or off are environmental influences. In regards to behavior issues, the social environment is especially important. One of the main purposes of the brain is in fact to interact with other brains.

Heritability is actually a mix of purely genetic influences and gene-environment interactional influences. There is no way to tell how much of each is present in the statistic. The determination of heritability can also be manipulated in a number of ways, such as by setting the bar for saying that a syndrome is present or absent. How much and how often does one have to drink to be an alcoholic, after all?

All human behavior, normal or abnormal, has a genetic component. That's because genes determine what the brain is capable of or incapable of, what it has a tendency to do and a tendency not to do, etc. They provide a range of options. They do not specify what behavior within that range will occur in a given environmental context. To say that genes play a role in creating a behavioral syndrome is a tautology.

In this post I will not go into more detail about what this all means. However, the absurdity of using heritability as a synonym for genetic is illustrated by a recent study published in the Journal of Adolescent Health (V.45 [6]:579-86, Dec. 2009) by van der Aa et. al. They looked at the heritability of high school truancy. The study pegged the "genetic" influence on this behavior at 45%!! Does anyone seriously believe that ditching school is determined by heredity?

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