An interesting tidbit in the nature vs. nurture debate is that nature and nurture interplay in ways you might not expect. For instance, height is approximately 90% heritable in the United States -- but this does not mean that in a vacuum height is mostly genetic. It means that in the United States nutrition has mostly been solved (and yes, even the "food insecure" in the US rarely lack for the actual calories which would impact their height -- food insecurity causes other problems) and therefore the only real differences that can remain are the genetic differences.

It might be useful to look at any twin study through this lens; if we know for sure the genes are the same and nature is off the table, how much variance remains?

Things get even fuzzier when you throw in heritable epigenetics too. We have a balance of these factors at least:

  - Genetics (DNA seq)
  - Epigentics (Histone acetylation, base methylation etc)
  - Brain wiring from experiences
  - Chemical impact from experiences, e.g. nutrition, toxins, sunlight, muscle dev etc etc.

I don't fully understand this blog post, but possibly of interest:

https://theinfinitesimal.substack.com/p/the-missing-heritabi...

In particular, see the third chart, "GREML-WGS heritability estimates," which shows that heritability for height is pretty much the same when they try to adjust for environment in different ways, while the estimates for IQ vary a lot.

Gusev seems convinced that some environmental effect is inflating heritability estimates for IQ that are based on twin studies.

> It means that in the United States nutrition has mostly been solved

Nature is not off of the table. We've just traded problems with calorie quantity to quality.

  condition           US prevalence
  hypertension        49%
  obesity             40%
  metabolic syndrome  40%
  prediabetes         38%
  fatty liver disease 25%
  diabetes            16%
  coronary disease     5%

In all these discussions it's helpful to understand the definition of broad-sense heritability (the statistic almost always in play when we're discussing heritability) --- it's a correlation, not a demonstrated causation, and your environment (and gene/environment interactions) are inherited as well.

Re: nutrition

I am curious about the influence on height by self-limited diets in children who are picky eaters. Is there some self-regulation process that decreases pickiness when nutritional status is at risk?

>and therefore the only real differences that can remain are the genetic differences.

Incidence of undiagnosed digestive and sleep disorders, like celiac disease and sleep apnea, respectively. "Catch-up" growth occurs almost universally after treatment starts, which means that the growth trajectory was lower than the "genetic potential", and likely remains so for children who can't access treatment.

Multiply across any number of silent or untreated disorders, sensitivities, or insufficiencies.

Adult height also isn't 90% heritable in the US. It only reaches that high a percentage of heritability in studies involving closely-related populations. In which case, of course; in populations with low genetic and cultural diversity and moderate or high variability, small differences are magnified.

That’s a good way to put it - eliminating other factors ends up deceptively making it look like genetics are the only difference. On the topic of IQ, the importance of those other factors is implied by things like the Flynn effect (https://en.wikipedia.org/wiki/Flynn_effect#Proposed_explanat...)? It’s also evident in how IQ varies by country. In developing countries, average IQ can measure low due to issues like malnutrition, access to education, etc. Those differences change as those countries develop or across different parts of those countries or when you track immigration populations from those countries.

Oddly, denial of these other variables has become core to scientific racism (https://en.wikipedia.org/wiki/Scientific_racism). For example, a Danish white supremacist named Emil Kirkegaard went so far as to create a fake journal (https://en.wikipedia.org/wiki/OpenPsych) to publish flagrantly incorrect papers on IQ that try to deny these factors and paint the IQ of non-white countries as low, with the only explanation being their “inferior” race/genetics. In fact, he just recently wrote a new “paper” (https://openpsych.net/paper/85/) that has been widely retweeted by supremacists on X.

As an anecdote: late 30s male, mother was 5'6 father was 5'9, I'm 6'4.

I have three kids with two different women. All 3 are blonde-haired/blue-eyed. I have brown hair and green eyes, my ex has brown hair and blue eyes, and my spouse has blonde hair and blue eyes. Not as interesting I suppose. Yes, they're all my kids biologically. :)

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