Correlation is not causation. Beyond just the fear of "cancellation", which certainly exists, any good scientist would want to find an airtight causal mechanism before publishing a socially and morally disturbing statistic that would hark back to unscientific eugenics movements from before the discovery of DNA.
And, call me a canceller myself, but somehow I doubt any such causal mechanism would actually be intrinsic to the human populations themselves. Such a strongly disadvantageous mutation as decreased cognitive ability would get weeded out by natural selection: you don't spend 20% of the body's calorie budget on an organ that isn't doing its job.
It saddens me greatly to think that scientists could not share data that they can't fully explain if it has any possible social injustice angle to it.
How many scientific breakthroughs across history took more than one person to figure them out and where subsequent thinkers built atop foundations and tidbits of those who went before them? (Almost all of them, IMO.)
Imagine if in the early days of AIDS, we couldn't talk about the role HIV might play in AIDS for fear that it would cast a negative light on communities affected by AIDS.
Imagine if we couldn't talk about the effects of parental, community, and early educational involvement in children's outcomes in life until we had perfect proof. Imagine we couldn't talk about the effects of inter-generational poverty until we had perfect proof.
"Until we have airtight causal links, we need to keep this quiet" is certainly not the way to make the fastest nor most effective scientific progress.
On the other hand in the day and age we live in we could certainly approach such an issue. The concept of 4chan is that everyone is anonymous therefore nobody ever gets special treatment based on their identity only the contents on that which they share. If you create a publishing platform for scientists that allows them to publish anonymously it will be the contents of the papers that will be evaluated strictly and no reputation damage is involved, maybe even let them digitally sign it in case they ever wish to show that they themselves wrote the paper if it became significant enough.
Anonymity is a weak (but better than nothing) solution to this problem.
The stronger solution IMO is "publish what you observed, what you conclude from it, what you think good next steps are, and provide your signature and contact information" and let people openly collaborate and build on each other's work.
Imagine if Linus Torvalds published the first version of Linux anonymously. Would we be in the same spot now as a technology society if collaboration were limited to anonymous, arms-length interactions on public channels?
Brain and body go together. Other animals have adaptations to their ecological niches. We have our adaptations to ours. Powerful brains are one of our adaptations to our niche, and an organism that has to live in our niche without our adaptations isn't going to do very well.
As soon as the cognitive capacity is sufficient for survival in some particular environment, there won't be any pressure for improvement of that, because it might in fact lead to maladaptive consequences, such as rise in depression and psychiatric disorders. Instead, there will be pressure for some physical fitness, improved immunity etc.
That's a misconception. The role of the brain our biology is not to direct somatomotor behavior, but visceromotor behavior. That is, the brain regulates the inside of the body. Increased cognitive capacity is largely directed to improving metabolic efficiency, immunity, and other basic bodily functions -- manipulating the external world is a bonus.
The higher levels of human intelligence are more useful for navigating the social than the physical environment, and obviously the social environment can vary drastically depending on where you live.
And, call me a canceller myself, but somehow I doubt any such causal mechanism would actually be intrinsic to the human populations themselves. Such a strongly disadvantageous mutation as decreased cognitive ability would get weeded out by natural selection: you don't spend 20% of the body's calorie budget on an organ that isn't doing its job.