Human brains were peak size few thousands years ago or something like that. Since then, average human brain started to shrink. I can't help, but think that's because of civilization freed our brains from the necessity to think as much, so evolution decided that spending so much energy on brain is wasteful and started to make it smaller.

I'm not really sure evolution works this direction today, we are not living in a food scarce world right now... But just food for thought.

"The brains of modern humans are around 13% smaller than those of Homo sapiens who lived 100,000 years ago.Exactly why is still puzzling researchers."

https://www.bbc.com/future/article/20240517-the-human-brain-...

Civilization cannot explain this trend.

Human brains are not the largest in the animal kingdom. Are elephants and whales smarter than us? We don't think they are, but we don't really know. It could be that they're much smarter but in different ways, maybe somatosensory or social or other ways we don't understand. It could also be that their brains are less efficient due to less selection pressure for efficiency.

In humans there is only a weak correlation between brain size/mass and IQ or other metrics of intelligence.

Then there's utterly wild stuff like this that reminds us of how little we really understand about brains and intelligence:

https://www.sciencealert.com/a-man-who-lives-without-90-of-h...

The fact that someone can function like this is incredible and indicates that the brain must contain a lot of redundancy, or something even weirder is going on.

Stuff like that is enough to make you wonder if we know anything at all.

Another similar data point is the spooky intelligence of many birds, like crows, who have tiny brains. Flying animals are under extreme selection pressure for efficiency because they need to be small and light, so their brains have gotten very efficient.