Intelligence vs education. On average, most humans have about the same baseline intelligence. Obviously some have more and some have less, but that's an inherent quality of our species, and the baseline is really only moved by evolution.
It can be hard to square the fact that intelligence and education are totally unrelated to each other. Ancient humans certainly knew less than we do now, but they were more or less just as intelligent as modern humans.
We can see from archaeology that ancient humans had language, sophisticated religions, and complex and vast societies. That's not something you can really accomplish with a significantly different baseline intelligence.
We know a lot more now and have a much more complicated global society, but mainly because we have machines to do a lot of the thinking and management for us. We're still just as intelligent as we always were, we just have tools to multiply our efforts now.
Humans today really are smarter, i.e., better at abstract reasoning--see the Flynn effect. That's partly due to better nutrition and lower disease load, but also due to modern education and lifestyles, which force people to learn to reason abstractly from an early age.
This is the nub of it - we're better at one very particular thing. I think I'm gonna get crucified if I really go into arguing against abstract reasoning as the baseline for understanding the world on this site, but without trying to defend that particular assertion I'd just make a note to say that what IQ tests are testing is a very specific type of thinking and not actually generalized intelligence, which is a very broad topic.
So, this isn't my area of expertise, but - I score very high on abstract reasoning tests, and I've been lucky enough to be around a bunch of people who are adept at things that at best require a whole lot more effort on my part to grok. I've got friends who can pick up a new language in a matter of months. I've got friends who can hear a song, know what keys it's in, improvise to it, extend it, and build complementary riffs to it on almost anything that makes a sound with more than one tone. I've got friends who can go into a room of children and have them all quiet and paying rapt attention in minutes. I've got friends who could sell an anchor to a drowning man, or have a dude in full biker gear and tattoos discussing their relationship with their mother and their childhood home. I've got friends who can read a book a day and tell you anything you ask about any of them and how they relate to each other. I've got friends who are almost telepathic in their ability to read and react to animals. I've got friends whose kinesthetic sense, ability to move their bodies, and ability to learn new physical movements is almost uncanny. I've got friends who can create absolutely stunning works of art that capture a feeling or a moment without any concrete imagery.
I am, and I say this without ego, a very smart person, and there are situations I absolutely excel - I can synthesize new information very quickly, I can draw correlations and relationships and principles from sparse data, I recognize patterns and build and dissect systems easily. Abstract reasoning is my wheelhouse, but I cannot do the things my friends can do with the ease they do them - I can get there eventually, in the same way that they can get to where I am eventually, but the things they do very clearly require a different type of intelligence than my variety.
The Flynn effect is about the change in measured intelligence through the 20th century. It tells us precisely nothing about the difference in intelligence between the 13th century and today, let alone going back before the Bronze Age Collapse or agriculture.
A large part of the Flynn effect may be due to reductions in environmental pollutants, which would mean it would be a reversal of the effect of the industrial revolution. Or it may have been due to people being much more used to taking tests. Or it may be due to nutrition. It is unlikely to be due to modern education forcing people to "learn to reason abstractly from an early age" because schools don't require students to learn to reason abstractly from an early age.
I think this is compounded by the correlation of beliefs between modern cranks who reject their education and believe what science now knows to be absurdities like "the Earth is flat" or "carrying this crystal pendant will please the gods and protect you from getting sick" with smart ancient people who believed the Earth is flat or crystal pendants will please the gods and prevent you from getting sick.
Yes, perhaps both Homer (the author of the world-famous literary classic the Iliad and the Odyssey) and a hypothetical modern Homer (d'oh!) believed in a flat Earth. The modern Homer failed to understand or rejected the education he was offered, while a hypothetical modern observer, who feels more intelligent than the flat-earther, understood and accepted it. But that does not mean that the ancient Homer was of similar intelligence!
It can be hard to square the fact that intelligence and education are totally unrelated to each other. Ancient humans certainly knew less than we do now, but they were more or less just as intelligent as modern humans.
We can see from archaeology that ancient humans had language, sophisticated religions, and complex and vast societies. That's not something you can really accomplish with a significantly different baseline intelligence.
We know a lot more now and have a much more complicated global society, but mainly because we have machines to do a lot of the thinking and management for us. We're still just as intelligent as we always were, we just have tools to multiply our efforts now.