And yet that can’t be limitlessly true; our brains wouldn’t be the size they are if they didn’t need to be for some reason. I’m reminded of accounts of people who’ve lost 2/3 - 3/4 of their brains due to injury, surgery, etc. and yet can live normal lives. They manage but one can’t help wondering just what they’ve lost that isn’t externally apparent.
Brain damage is different from a brain that evolved to be smaller. I’m pretty sure crows are smarter than sheep, despite having much smaller brains. Just because it was easier for humans to grow bigger brains than to develop intelligence via some other pathway doesn’t mean there aren’t other possibilities.
I find the limitations based on interacting with the rest of the physical world more interesting to specialists about, anyway.
This is going to age well in 20 years when someone resurrects this thread.
Again, bird brains are very different from mammal brains, so the intelligence of crows doesn’t say much about how small a human could be.
hmmm … not sure about the half a meter … all of our girls were taller than that at birth (and that newborn-helplessness probably colours my perception) … that seems too short to walk for longer distances, etc… so being really small is probably not much of a help for H&G-societies) …
100cm+ makes a lot of things easier than 50cm …
But still, I recall making myself taller on a sign-up-form (age 13?) to land an agricultural job for a day … and boy, did I suffer that day, as pretty much all work was above head level… extremely tedious.
so being smaller seems more of a con than a pro for hunting and gathering
But smaller creatures don’t need to eat as much, so they don’t need to hunt or gather as much. And a lot of gathering is from stuff on the ground, and “don’t have to stoop” is a win. Abd it’s also easier to climb if you weigh less.
I suspect that we are the size we are kinda by accident. It happened to be an ape about this big that specialized in brains. But i suspect it could have been a different sized ape.
The website linked below lists 16 people from all around the world who are or were between 21.5 and 29 inches tall. They seem to mostly be of average intelligence. I suspect that if there were 31,000 people of that height, one of them would have an I.Q. of at least 160, as is true of a similar group of people whose heights are spread over the usual range. There are certainly some very short people who are, say, 4’11" and very intelligent. For instance, Greta Thunberg is 4’11". Kristin Chenoweth is 4’11" and seems fairly intelligent. I’m 4’11". Am I very intelligent? Does height have anything to do with intelligence?:
given the square/cube law in sizing - that you seem to imply (a person 2x as tall would have 4x as much surface, but 8 times the volume) - which you rightly say needs to be fed …
but also more volume per m2 skin allows for more temp resistance …
so my (somewhat educated) guess would be that “half-size-people” would have to live nearer to the equator and are less likely to thrive the further you move away from there …
Anecdotical information seems to support this (both small peoples mentioned upthread (yep … n=2 …) live in tropical environments)
I “think” not … we have collectively grown 10cm on avg. over the past 150 or so years … that is mostly nutrition/kids-health related. So the gold-fish effect (growth related to environment/food) seems to be in place…
Its interesting that a lot of what we are debating here is happening right NOW, but we are notoriously bad at seeing slow and long-term patterns.
I am certain we’ve done this topic in the past. I cannot come up with a unique enough search to find it though. I don’t say that to complain about the OP, but to maybe trigger some of the other old-timers to remember what they wrote or some tidbit they read that stuck with them.
I do my most successful searching when I recognize the topic and can recall some turn of phrase or keyword(s) I’d used in one of my post(s) to that thread. That’s usually unique enough to return a tolerably short list of threads to dig through sequentially.
This ring a bell for anyone else?
I suspect that a certain amount of intelligence requires a certain amount of brains.
Also, larger animals have fewer predators.
We are animals.
Not sure if this is the one but this was a cogent point made by @engineer_comp_geek in a different thread.
And this thread!
Nicely done there @DSeid; the first one you cited was what I was thinking of, but the other one is on-point too.
My wife always asks me to find things, but usually it’s a fallen earring or such … 
Generally, but songbirds are small and have few predators because they are hard to catch. Smart animals are also hard to catch.
But my bigger response is that i don’t see any special reason that fewer predators would lead to more intelligence or more development of culture. That’s the assumption you are making that I’m not following.
There’s been no evolutionary advantage to have smaller (physical size) brains.
There is a lot of wasteland in the brain, there’s also hardwired stuff going back to primitive days like the Amygdala. If you were going to build the human brain from scratch to suit modern society, you wouldn’t end up with what we have now, but it’s what we have.
There’s probably been a number of people with well functioning smaller physical brains born over the millennia, but they obviously weren’t considered attractive enough to mate and pass it on.
The key point, as mentioned, is that we seem to fll in a sweet spot fo the square-cube law. Twice the head size gives 8 times the brain matter. While it seems radically smaller head sizes seem to match average intelligence, in general the rule of thumb for intelligence is brain size -but also the use your brain is put to.
Also, humans learned to hunt - there’s allegedly a connection between the process of learning upright walking and running, our ability to run down larger grazers to exhaustion and then kill them with tools, which lead to the higher level of meat consumption (protein) which fed our brains, allowing them to grow even bigger - a positive feedback mechanism. This also allowed the processes of weapon development and cooperative coordinated action that made us dangerous to predators much bigger than us. The brain allegedly uses a quarter to a third of the nutrition we consume, so development of intelligence would require that the evolving creature have a similar means to hunt or gather large amounts of food.
But the key there is running. We can harry herd animals to exhaustion. Presumably a significant smaller human would not be able to run down a buffalo or wildebeast. Goats? Sheep? But then, the predator-prey feedback cycle is probably why there are large herds of cow-sized animals grazing on grasslands, while deer and goats are confined to forests and rocky terrain. Perhaps out monkey-humans could hide in the trees and drop spears weighted with rocks onto deer from above.
The size of a woman’s pelvis (the wide hips) is the best compromise between brain size (to fit through the pelvis) and skeletal integrity - any wider a set of hips runs the risk that the torso is too heavy and the hips break. As it is, birth is a difficult and risky process (so I’m told) because of the size of a baby’s head. Plus, we produce babies much like marsupials, but without the pouch - requiring a significant amount of further development time on the outside (where babies are more vulnerable) before they are even able to walk and feed themselves on normal food. I suspect those 4’11" people generally had roughly normal-sized mothers and a quick browse of Greta images does not seem to indicate she is more pin-headed than normal. I suspect for height, head diameter is the least variable body proportion.
Worrying about walking assumes big heads are atop baby-leg-sized bodies. I presume a smaller species evolved for fast running would have longer legs and a less long torso to compensate.
(However, pictures of pygmies seem to indicate that a fairly small diameter head is not an impediment to brain function.)
Something like fire - again, depends on environment. We deal with trees a foot or more in diameter routinely. I don’t see a 3-foot creature or even 1 foot having trouble finding kindling using the appropriate tools. Pacific Northwest natives fells massive trees by gradiual means, using things like girdling, sharp rocks, and hot rocks from the fire to char away the trunk. More likely, their civilization would have to be more advanced - develop better clothes - before venturing outside the tropics. Or due to smaller size, would they more likely keep their fur? Evolution made us shed our pelts in order to shed heat while running during hunts.
The square-cube also affects things like falling. Smaller animals can fall further than humans relatively, because they weigh a lot less for the surface area wind resistance (terminal velocity).
But there is, at least for brain size at birth.
Which makes me wonder why the human brain needs to develop so large before birth? After all, like everything else it starts from a few simple cells. Why does it neeed to develop so much before birth, when a baby is essentially a helpless form of external fetus for the first several months after birth.
Brains are odd. We are born with essentially all the neurons we will ever have. During development the brain is created a bit like an integrated circuit. It fills with neurons, and then a huge culling takes place, leaving behind the neurons we are eventually born with. However the brain is only partially myelinated - only the basic bits of brain needed for a neonate to start life have myelin around neurons. All the others are thus unable to propagate signals, and are quiet. As we grow, our skulls expand and there is room to fill out and activate the previously dormant capabilities. Then they can become active and start to build connections and become useful. This takes at least the first couple of years of life.
One might imagine that this path evolved to keep birth head sizes small without changing the process by which brain structures are built.
Wait what?
A huge culling of neurons? Connections between neurons increase during most of the first year of life then get pruned in further development but I was never aware of neurons getting culled to any significant degree.
Lesser myelinated neurons are quiet? Also not something I have ever heard before.
Huh?