This also assumes that IQ testing has remained static. It has not. IQ tests continue to evolve and there are >1 of them and they do not all agree. I.E. the tests themselves might be responsible for some of the variance.

how does one separate "doing good" and "stop doing harm"?

I'd personally count nutrition squarely in the second category

coppsilgold is the one who made a hard-line, clear-cut dichotomy when they said "it's easy to do harm [but] it's all but impossible to do any good". bglazer referenced several interventions that are known to increase IQ which challenge this dichotomy. Saying that it is difficult to separate "doing good" and "stop doing harm" is agreeing with the point that coppsilgold created a distinction without a difference.

The recent marathon world records are apparently due to improved nutrition.

Here's the producer of the hydrogels talking about the exact process of getting the maximum carbohydrates into the runner:

https://maurten.no/blogs/m-magazine/how-sabastian-sawe-fuele...

> At the elite level, marathon performance is defined by energy availability as much as physiology.

> Maintaining a pace of 2:50 per kilometer requires a constant supply of fuel. Even small disruptions in energy delivery can result in significant time loss.

Also we are past that. Now IQ started decreasing.

it's hard to separate IQ decreasing and return to mean with IQ stabilizing

in 20th century most of the world moved past famine and toxins - did any factor of similar scale happen in 21st century as well to start looking for opposite processes?

The people that have bad factors in IQ bred faster than ones that had good factors in IQ.

Birth rates drop the higher developer countries is and the growth of population in those (excluding mass migration) pretty much stopped and reversed

Generally that statistic refers to populations in isolation, not the entire world in aggregate.

It is fairly well agreed upon that American kids across the nation are currently testing lower than they were in 2010.

Maybe across the whole population because most people were struggling to eat enough and received almost no education.

If we compared average modern humans against average well fed and educated ones from 200 years ago would that still hold up? I suspect the average college educated human from 1800 would obliterate the average college educated human from 2026.