Again, this is the core fallacy of eugenics.
How many current US PhD's are the children/grandchildren of immigrants from underdeveloped countries who lacked education and worked manual jobs (or maybe even went through extended periods of unemployment)?
Why are you conflating immigrants from underdeveloped countries with low intelligence? The parents could be have been (likely were) highly intelligent, just lacking the opportunity or access to education.
The current US PhD's that are the children/grandchildren of immigrants aren't a random selection, they are the product of smart motivated parents working the system (immigration system, education system, admissions system) for and with their children.
The core fallacy of Eugenics is not that intelligence is heritable, it is that you can avoid terrible moral hazards when you try to meddle in this stuff.
I'm trying to say that regardless of who your parents are, your intelligence is primarily driven by your education (and your attitude towards education), with slight variance for genetic factors.
Therefore, we should not be anxious about "dumb people reproducing en masse" (as GP was).
We should be worried about educating everyone equally and fairly.
I don't think 50-80% heritability should be hand-waved away as "slight variance". I think what you're talking about is the manifestations of the intelligence (i.e. you can't be a rocket scientist if you never had the chance to learn about it), but not the intelligence itself.
Also please cite actual studies rather than Wikipedia. You’ll capture more nuance.
We conclude that there is now strong evidence that virtually all individual psychological differences, when reliably measured, are moderately to substantially heritable
For example, citation 6 implies nearly every personality trait is inherited, which seems aggressive to me.
Citation 7 is a book about how the genetic links get stronger with age, which seems also odd to take at face value.
Anyway, as great a source as Wikipedia can be, I wouldn't take its summaries at face value.
I don't have the time to work through the math concretely, but intuitively, imagine that the intelligence of parents is normally distributed, and the intelligence of their children is a tighter normal distribution around the parents' intelligence. Set the cutoff for "participating on HN" to to some threshold. Given the right set of parameters, most of the "weight" in the aggregate child distribution above the threshold will come from the long tails of the child distributions of parents in the fat part of the parent distribution.