True. Humans are pretty unique in that regard, though; pretty much no other animal is like that. It's easier to understand human neonatal development if you just considering all humans to be born premature. (It'd be really interesting to know whether that's literally true—whether keeping a human baby in the womb for an extra few months would actually result in the same stages of mental development being passed that occur in a regular baby of that age who has been sensing and interacting with the world.)

I've read somewhere that we are basically born prematurely (as you said) because if we waited any longer then our enlarged head sizes would make delivery quite possibly fatal.

My brother was born a week or so after his due date; they induced labor for him for exactly this reason. Perhaps unsurprisingly, his head circumference was literally off the charts.

Maybe off-topic, but that's one side of the coin, and I suppose the other is that being exposed to more sensory input accelerates development, or makes it even possible (on higher levels of cognition). If this wasn't the case, why wouldn't we just be bigger and carry longer? Is size viz megafauna really that suboptimal for any more significant reasons than being hunted human hunters? I would almost say that longer pre-natal development was suboptimal, because we'd either become bored, or supersmart, but anyhow superegoistic for lack of nurture.

Calling it premature is ironic, if we reach nominal maturity only after 10 or more years as far as fertility is concerned--the equivalent in AI would be the procreation of a neural net, perhaps after exploiting a bug in the game, breaking out to rewrite a better version of itself, or colluding with itself in self play. Yes, this is going off-topic.

> why wouldn't we just be bigger and carry longer?

The consensus in the evolutionary-anthropology community is that our hips (pelvic bones) have to be the size they are, in proportion to the rest of us, to make us able to walk upright. "Building bigger" doesn't really work, for the same reason that you can't make a giant robot—if you scale humans up, the pelvis would need to be made out of something stronger than bone to support the additional load.

The same is not as true, though, if you just make the person wider—because then you spread the same load over "more pelvis." (This is just a personal unfounded hunch of mine, but I think some human subgroups—e.g. midwestern Americans—who are at the genetic limits of baby head size, and who avoid C-sections, are currently selecting toward bigger-boned-ness.)

> I would almost say that longer pre-natal development was suboptimal, because we'd either become bored, or supersmart, but anyhow superegoistic for lack of nurture.

Keep in mind that we wouldn't be conscious for any of it. The development stage that "wakes you up" to the outside world would just occur later on, as occurs in animals with longer gestation periods (e.g. elephants, with a gestation period of 18-22 months.) This would give things like your ocular layers longer to finish developing, without really having an impact on the parts of your brain that learn stuff or think stuff.

Hypothesis:

Being born “prematurely” might allow for more flexible brain wiring. Adapting better to an environment quite distinct from ancient ones we had evolved in is possibly one of our key cognitive advantages compared to other animals.