"But back to the question: What does heritability mean? Almost everyone who has ever thought about heritability has reached a commonsense intuition about it: One way or another, heritability has to be some kind of index of how genetic a trait is. That intuition explains why so many thousands of heritability coefficients have been calculated over the years. Once the twin registries have been assembled, it's easy and fun, like having a genoscope you can point at one trait after another to take a reading of how genetic things are. Height? Very genetic. Intelligence? Pretty genetic. Schizophrenia? That looks pretty genetic too. Personality? Yep, that too. . . .
"Unfortunately, that fundamental intuition is wrong. Heritability isn't an index of how genetic a trait is. A great deal of time has been wasted in the effort of measuring the heritability of traits in the false expectation that somehow the genetic nature of psychological phenomena would be revealed. There are many reasons for making this strong statement, but the most important of them harkens back to the description of heritability as an effect size. An effect size of the R2 family is a standardized estimate of the proportion of the variance in one variable that is reduced when another variable is held constant statistically."[1]
[1] Turkheimer, E. (2008, Spring). A better way to use twins for developmental research. LIFE Newsletter, 2, 1-5
http://people.virginia.edu/~ent3c/papers2/Articles%20for%20O...
I am totally confused. My understanding is that heritability is a measure of how much genetics accounts for the observed variability in a given environment. I understand both that we don't understand the genetic recipe for height, but also that identical twins grow to be the same height. What is the author saying that I am missing?
Having now read the paper, yes, that was what he was saying, and the non-quoted sections of the paper are much clearer. Example
For the modeling underlying twin studies to make sense, one has to assume that the environments experienced by identical twins raised in the same family are no more similar than those experienced by frater- nal twins, that genes and environments are independent and additive (again, in the usual ANOVA sense) in the determination of the trait, and that parents mate randomly with respect to the trait.
That's totally true. If you compared an organism with a randomly generated genome to a human and exposed both to what would be a normal range of environments for a human, you would find that all traits are entirely genetic. And if you selected people from the normal range of human genetics but only gave half of them access to important things like a uterus then you would find that all traits are almost entirely environmentally determined. So you can't say that "Trait Foo is 50% heritable" unless you also specify the populations and range of environments you're talking about.
EDIT: Or you could say that heritability is ordinal but not cardinal, given some reasonable assumptions.
As long as you can't tie intelligence to particular genes, as long as you can't tell what amount of intelligence in an individual is inherited, and how much isn't, there is no use for this in education, politics or social welfare.
What I see the argument being used for, mostly, is to justify racism and entitlement issues in wealthy people...
We can reject the existence of an observed natural phenomenon because we can't explain it. We still haven't unified gravity with the standard model, but that doesn't mean we reject that gravity exists (for practical purposes or otherwise).
The fact that a natural phenomenon might be socially inconvenient is even less of a good reason to reject its validity.
Finally, I don't even see why it should even be so socially inconvenient. Say the experiments are right, and intelligence is mostly heritable rather than a result of education, upbringing, etc. Why should that justify entitlement on the part of the wealthy? Indeed, it should cut across that grain. If its mostly heritable, being intelligent shouldn't be seen as intrinsically virtuous any more than is being tall. Moreover, the heritability of intelligence may very well imply a need for a change in our priorities when it comes to social welfare. E.g. maybe we need to de-emphasize education, and divert resources to building up social and family networks.
"Socially inconvenient" doesn't even come into it, because twin studies don't tell us anything about differences between two ethnicities. For that matter, genetic diversity within populations might have a larger effect...
The "intelligence is genetic" "fact" is often used to justify refusal to tackle socio-economic problems (like "under-achievement" in blacks or hispanics in the US, or the turkish minority in my home country) with socio-economic solutions. Because hey, it's all genetics, so we can't change it. Even if measures for improvement have been proven...
The fact that intelligence is heritable says nothing about social-economic policy for changing the environment. It is as absurd as saying that because "height is genetic" there is no reason to worry about malnutrition.
Changing it wouldn't make a difference, everyone using that logic isn't basing their end goal on it, simply using it to justify their feelings.
Hell it took a while for me to understand the benefit of such improvements, and it had nothing to do with genetics. My problem was few people talk about the socio-economic impacts on capabilities, and the fact that counteracting programs can theoretically stop the death spiral in those groups.
However there are a lot of people who can't get over "not like me" and think the whole thing is a waste because it takes away from "hard working young men".
The fact that a 'wrongness gene' hasn't been, and may not ever be, identified does not undermine my assessment, but rather indicates current models of the interaction of genes and wrongness might be naive, and the interactions are probably deeper and more complex.
To take an extreme example where genetics is the clear cause, cats are underrepresented in college. Because we know that cats are genetically less intelligent than humans, we can conclude that affirmative action/college for cats education programs/etc are a waste of money.
Another use would be knowing that if only 50% of the population has the intrinsic intelligence for college, college prep programs should not serve more than 50% of the population (modulo technical details).
Not saying it's moral, but definitely and obviously practical.
Pedigrees and genetic testing in animal breeding are way more useful. But there you have completely different structures and goals. And some of them, particularly diseases with high heritability like canine hip displasia, can't be solved by current genetics yet.
> Although the exact figures have been the topic of much debate, the claim that IQ is at least moderately heritable is widely accepted. IQ may in fact be similar in heritability to the physical trait of height
What the article is saying is that intelligence cannot be tied to particular genes:
> We sought [and failed] to replicate published associations between 12 specific genetic variants and g using three independent, longitudinal datasets
It just goes to show that there isn't necessarily one particular factor you can pick out to predict intelligence; it is a combination of many things.
(I shall attempt to avert the impending discussion about the word "intelligence" by clarifying that the sense I am using that word is in the same specific manner that the article is: as an objective measure that is statistically correlated with other measures).