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Comment by ren_engineer | Hacker News Reader

people really don't want to accept that beyond the most extreme cases(starvation, lead poisoning, complete neglect, no school access at all, etc.), environment really doesn't play that big of a role. Twin studies have shown this for literally decades

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That’s not what the twin studies have shown. It’s not only the most extreme cases, it’s anything short of the very good circumstances. For example, the stable homes families have to prove they have to adopt.

Cyril-f “twin”. https://www.robkhenderson.com/p/no-one-expects-young-men-to-...

That's not true, for example metacognitive ability studies have shown environment plays the dominant role. Twin studies on trust provide the same, in which genetic component while large at 33% certainly doesn't indicate what you're stating that it's only "extreme cases". Even in studies re-assessing conventional twin studies and educational attainment, the conclusion was that while some is genetic (sometimes even a large portion) the correlations between a mother and father's educational attainment points to environment playing a large role (unless you have the belief that the mother and father are siblings I suppose).

You'll be extremely hard pressed to find researchers conducting these twin studies who minimize the role of either genetic or environmental impact on certain aspects in the way you did.

There's a tricky (and super interesting) thing with IQ studies. Environmental factors play a dominant role early on, but genetics becomes more and more dominant as a person ages; significant privilege or disadvantage earlier in life notwithstanding (excepting major physical impairment by nutrition, lead, etc)! Most studies tend to find the heritability of adult IQ at around 80%.

Any research on this area is walking on egg shells and so researchers are highly incentivized to overemphasize possible environmental explanations. Nature formalized this threat/risk with their relatively recent announcement [1], but it seems to have been an unspoken 'rule' for decades at least.

[1] - https://www.nature.com/articles/s41562-022-01443-2

Heritability is not genetic determination; your environment is inherited as well.

The Nature link you've provided doesn't address anything you wrote in your comment.

Heritability is, literally by definition, the measured difference in some value (like IQ) between people that is attributable to genetics alone. There's quite a lot of clever ways to control for environmental factors, like twin studies. And I simply think you're not engaging in good faith whatsoever if you don't see how that Nature article creates a huge chilling effect on any discussion of genetics.

Heritability is the ratio of genetic variation to total variation. Lipstick-wearing is highly heritable; the number of hands and feet you have is not. As I said, and as you can see, the heritability of a trait tells you nothing at all about its genetic determination.

I don't know what to tell you about the cite you gave, since it simply doesn't say what you said it says.

You sound like you're thinking of things colloquially, to put things in a kind way. Heritability is not a colloquial term and in biology/genetics refers exclusively to genetic factors. In particular it's the percent of difference in some value that cannot be explained by non-genetic factors. So e.g. if my IQ is 130 and yours is 90 then we'd have a difference of 40 points. With an adult IQ heritability of 80% we'd expect that about 32 points of that would be unable to explained outside of genetic factors.

Heritability does change over time because environments change over time. For instance in an area where starvation, lead poisoning, and malnutrition was common, the heritability of intelligence (or height) would generally be quite low, because the aforementioned environmental factors would be able to explain a large chunk of the differences between populations. But in a society where everybody had practically identical relevant upbringings and opportunities, the heritability of intelligence would be 100%, because the only difference between people would be genetic.

One of the many ways to test for heritability is twin studies. You'll likely find the correlation between lipstick wearing between identical and non-identical twins would be near to 100%. This means that the heritability of the trait would be near 0%.

No, I just provided you the literal technical definition of "heritability". It should be immediately apparent to you why lipstick is (highly) heritable and hand count isn't†; if it isn't, you're the one working from the "colloquial" understanding.

† lipstick: highly dependent on XX vs. XY; hands: set by highly conserved Hox genes, variation virtually entirely due to environmental factors.

I'm going to assume you're not trolling, and I am also going to assume you're the type of person that would take Wiki as a reliable source, so here you go:

---

"The concept of heritability can be expressed in the form of the following question: "What is the proportion of the variation in a given trait within a population that is not explained by the environment or random chance?"[2]"

---

The within a population part is critical. I'd encourage looking up twin studies to understand one way this percentage is estimated. I assume you think you know how they are done - you do not, because it directly leads into an understanding of how things like lipstick wearing would be near 0% heritable, while things like handcount at birth would be near 100% heritable.

[1] - https://en.wikipedia.org/wiki/Heritability

I'm not making up that lipstick is heritable; it is a classic example of a non-genetically-determined heritable trait, as is hand count (in the other direction). I think you need to do some more reading: you are clearly using the term as a synonym for "genetically determined", and that is simply not what the heritability statistic tells you.

For what it's worth, you can mechanistically work out lipstick and hands from first principles; just plug rough numbers into the formula.

When you say things like lipstick wearing is a classic example of a non-genetic heritable trait, you sound like a guy claiming that a cat is a classic example of a non-reptilian reptile. It's somewhat of a contradiction in terms that doesn't make much sense.

"Heritability is a statistic used in the fields of breeding and genetics that estimates the degree of variation in a phenotypic trait in a population that is due to genetic variation between individuals in that population."

You are using the term in a colloquial or folk sense. Do you think accents are highly heritable? After all, a child will almost always share the accent of their parent. So in the colloquial sense this would be a 'heritable' trait, but in the genetic sense the heritability of an accent is zero.

Lead poisoning isn't an extreme case, it's a very common problem.

Twin studies don't exclude environmental causes because twins have the same maternal environment.

Yeah, I never got how the womb doesn't count as an environment, and even the circumstances that led to the twins being separated.

While commonly thought, this isn't how twin usually studies work. The way it works is you look at the correlation between identical and non-identical twins on some given thing. If there's a much stronger correlation between the identical twins, then it's probably primarily genetic. What this does is helps to eliminate environmental factors because identical vs nonidentical twins will both be raised in basically the exact same environment.

So take height. If identical twins have identical heights while non-identical twins have varying heights, then it's safe to assume height is largely genetic. Interestingly separated twins would actually be worse in many cases because you reintroduce environmental deviation. For instance with height, differences may well be down to e.g. nutrition, but when you have them in the same household you can usually assume roughly identical nutrition.

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