What Heritability is Not
Because so many people abuse or misunderstand the concept of heritability, I decided that it would be nice to have a list of what heritability is not in one place. If you have questions or if there is a misconception about heritability you’d like me to address here, feel free to comment. This post will serve as an updated reference.
- Heritability is not an indicator of malleability. Entirely genetic disorders such as phenylketonuria can be cured through the proper diet.
- Heritability is not a measure of straightforward genetic effects. For example, genes that affect physical appearance have an effect on personality development.
- Heritability is not independent of the population. It may differ from one group of individuals to the next, because groups differ environmentally and genetically.
- Heritability is not independent of age. The effects of genes or environments may grow in potency through development.
- Heritability is not an indicator of the causes of group differences. A trait can be highly heritable, as in the crop field metaphor, and group differences may still be due to environment. This applies also in the real world situation for humans, where the environmental differences between groups are not as systematic.
- Heritability is not necessarily homogeneous within a population. A heritability of 50% may be hiding the heritabilities of 40% and 60% in subgroups.
- Heritability is not a measure of intergenerational transmission. A trait may be highly heritable but not pass on from one generation to the next. This is because the relevant genes and environments may differ from one generation to the next.
- Heritability is not a statistic for individuals. If you are using your knowledge of heritability to understand a single individual you are a biographer, not a scientist.
So, some of you may be wondering, why is heritability a useful statistic? That’s easy to answer: it’s a measure of how much phenotypic variation in a given population at a given time is due to genetic variation in that population. Measuring heritability allows us to say that, for adults in the modern world, variation on IQ and personality measures is primarily due to genetic variation. That’s a pretty remarkable, and important finding if you ask me.
Labels: Genetics
Years ago, I read an undergrad psychology textbook that came right out and said, “When you can’t identify the cause of a behavior, you describe the cause as ‘genetic’.”
Tell this to the “Human BioDiversity” crowd.
They seem to latch their whole skewed perspective of everything positive and negative about certain groups on static genetic heritability.
***Tell this to the “Human BioDiversity” crowd.
They seem to latch their whole skewed perspective of everything positive and negative about certain groups on static genetic heritability.***
I had this idea that narrow-sense heritability was the expected correlation between two individuals that would have exactly the same genotype, but would live in randomly picked environments.
But if gene-environment interactions are accrued to narrow-sense heritability, I guess I was wrong. Perhaps you can add this to your list? Or is it subsumed by the “not independent of environment” point?
Same genotype in random environments is the broad-sense heritability (also called the clonal repeatability)
actually, i think you may be right and that i erred. narrow-sense heritability is intended to be a measure only of simple additive genetic effects.
so, orion,
really, the point i made applies to measurement. gXe is not supposed to be part of heritability (narrow or broad sense), but it ends loading on that part of the estimate. twins reared apart studies can avoid this somewhat, by making shared environmental similarity significantly less.
“Heritability is not
I’m not sure that heritability is not a statistic for individuals. If a son and a father exhibit the same personality disorder, is it wrong to consider heritability estimates for that disorder if we wish to understand its mode of transmission (genetic vs learning/cultural conditioning).
In particular, I’m thinking here of the case of Marc Lépine, who was responsbile for the mass murder of 14 women twenty years ago. Both he and his father showed similar psychological characteristics, in particular low thresholds for ideation and expression of violence (a ‘quick temper’ in plain English). The most popular explanation is that Marc inherited these characteristics through social and cultural conditioning, even though his father left his life at the age of 7 and even though Marc hated his father (to the point of changing his name and reproaching his mother for not doing enough to protect him from his father’s rage).
To my knowledge, no one has ever suggested that the mode of transmission here was genetic. In fact, most people seem to argue for some kind of early childhood conditioning. Yet heritability for violent behavior in boys is moderate to high when we look at adoption and twin studies. I’m aware of the weaknesses in using heritability estimates. But is this a reason for not mentioning heritability when discussing individual cases, like Marc Lépine?
I agree that we should consider heritability when discussing cases like that, but we should not be under the pretense that we’re speaking scientifically when we attribute their behavior to genetic or environmental causes.