>Can we be so sure?

We have enough studies on the impacts of nutrition in the womb and the impact of experience and neglect on brain development in children that we can be sure that intelligence is more advanced. More complex languages leads to more complex thoughts. Better nutrition leads to greater intelligence. Both for our normal communication but also for languages to describe abstract ideas like mathematics.

If this still doesn't sound definite, then I think we are getting into the issue of what is intelligence and how do you measure it in a person or a population. But then we would need to get into answering just how can we be sure humans are more intelligent than a wide selection of animals and even non-animals. Same for creativity and sophistication.

I think a lot of this discussion can evolve around definitions.

If we look at history back until the industrial revolution, I would guess that less people had to work on food production and thus could go into creative fields.

Intelligence is better measurable through IQ tests and we can see IQ score rising in societies today. (Flynn Effect)

Intelligence is also highly context-specific. Context today is not the same for the average human 200 years ago, even more different 2000 or 20k years ago.

I'm not sure high IQ people from today would make it far in more ancient times, and not because smarter or dumber, but only because they are unadapted.

> Intelligence is also highly context-specific

It's not though. It's the opposite, and that's what makes it interesting, and why it's being measured. The g factor: https://en.wikipedia.org/wiki/G_factor_(psychometrics)

General intelligence is related to the ability to learn new things in general, no matter the context.

And today's humans, would, if they got to start as babies 20k years ago, learn all there was to know, about that world. And they'd start feeling bored. Maybe they'd try to build and invent things, just to escape the otherwise for-the-brain empty days.

(You somehow got it the other way around :-) I wonder how you formed your opinions / beliefs about intelligence? If it's ok if I ask)

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If, in your comment, replace IQ with "wisdom" and "knowledge", then it makes sense. A grown up human of toady -- yes, definitely unadapted, knowledge wise.

> And they'd start feeling bored.

Likely not. Agafia Lykova is not bored, she‘s still not using any of the modern technology and she’s still living like her ancestors lived 500-100 years ago. And she was young when her family was discovered.

https://en.m.wikipedia.org/wiki/Agafia_Lykova

But there's around 10 billion people on the planet, you can always find some unusual person to make a point.

In this case, though, she might agree with me, I'd say -- in that she spends part of her time reading and constructing things, from the article you linked: "reading and construction".

Modern tech? I think there's lots of cool not-modern tech, ancient tech.

Edit: She's an amazingly cool person! Thanks for linking the article, I might have a closer look at her & her life (now done. I wonder how many books she has to read, and after how long she's forgotten them so she can re-read)

Edit2: Sorry if my first version of this post sounded a bit grumpy. Now edited

My point is, our intelligence requires some activation. It is context-specific in the sense, that pure brain cannot develop it alone, in isolation or in a low tech culture. Configuration of our brain takes time and education, so modern human in prehistoric context may not reach the same IQ as if this person would have studied in one of the best schools on this planet. Agafia is modern human being, but she never had a chance to learn all the things that others had access to. When she met the civilization, she was already an adult person and her ability and desire to learn more was limited. She ran away from civilization back to her hut in taiga, and never wanted to live another life. She does not read a lot and, if you watch the documentary about her, she‘s reading Bible or books for children, so it’s not the same being fond of reading as for someone with university degree. She is unusual, yet she is normal, and she is a good illustration of what would happen if modern human had to become a hunter-gatherer, losing almost all cultural baggage except faith.

Do you have evidence for statisticly significant increases in IQ that persist into adulthood as a result of education?

Success in education is correlated with high IQ. Much the same way high IQ is correlated with many forms of success.

Education does actually raise IQ.

https://pubmed.ncbi.nlm.nih.gov/29911926/

…Whatever that means. It's meaningless to say fluid intelligence can't be improved with education, that's a tautology.

... we did not identify any studies that tested whether these effects persisted into adulthood. These estimates should thus be regarded with caution.

This is fascinating, and now I've fallen down "See Also" Wikipedia rabbit hole. I'm glad you shared this.

If today's humans got to start as babies 20k years ago, their IQ as adults would be correspondingly lower due to poor nutrition while growing up.

200 years is not long time ago, the changes may be subtle. I’m not aware of any research in this field, but mass education improves our cognitive abilities and I won’t be surprised to see if natural selection favors those who respond to education better. Our species developed new ways to pass „genetic“ information to next generations beyond DNA. We may be almost the same as ancient human right after birth, but we acquire and encode in our behavior and body much more extra information as we grow. Our biome adjusts to our food habits, our hormonal system adapts to our level of stress, our immune system gets upgrades via vaccines etc etc. And all of this is controlled by our intelligence.