Considering the large energy needs of the brain, there is an evolutionary pressure to make it smaller... so something pushed it the other way.
Are there any evidence for a period without meat in the diet, to start with? Considering that teeth are hardy, this will probably be testable in our lifetime.
I've rather seen claims that the brains were larger before civilization, following the hypothesis that it is hard to live as a hunter gatherer. (And then it was with lots of meat in the diet.)
We do know that calories have been a limiting factor for most life, generally also including humans. iirc, 20% of the energy need goes to the brain. The brain size would vary a lot, if it really didn't make a big difference.
Consider that the evolved tendencies for getting diabetes are there because it made it easier to handle periods of hunger. So sure, that might be much later, but...
And also, eating those starches needed cooking for humans, afaik? Which needs some brain power (there was not time to evolve instincts). We lost a lot in the jaws and teeth to get the brains. (Couldn't have both.)
Then, there was news just a week or two ago about a new result -- humans put "building capital" into our brains rather than our muscles, which is why most monkeys while large as children can tear a human's arm off and beat our head in with it... Brains are expensive.
I might add that there have to be a hard evolutionary pressure to build complex organs, like the extra stuff in the human brain. It is hardly just more neurons added to earlier monkeys (evolution is hill climbing, so you will find simpler/different analogues in other primates, but it isn't just adding some volume and e.g. <miracle> language circuits :-) ).
And so on. This list could probably be longer. :-)
Apparently there is evidence you need a pretty big brain and speech abilities to run a net energy positive fishing village. A neanderthal should be able to catch fish, just not efficiently enough to live off a fishing culture. Their trash piles have all kinds of bones, just not fish bones. Ours are/were full of fish bones, anywhere there's fish.
Fishing might have been "the niche" that led to our species... starting with older hominids who were better than average at gathering fish due to some local geologic peculiarity (the perfect river to catch salmon by hand occasionally or whatever), a zillion generation later of ever improving therefore ever fatter fisherman and we got a prehistoric Captain Ahab filling the tribe trash piles with fish bones and the non-homo sapiens cousins can't fish compared to us and die off because we're fat from fish and they aren't.
Large amounts of starch would seem to require agriculture which is pretty recent compared to fishing.
Our "ancestors" really thrived for the most part of the very mega-fauna we helped extinguish.
> Their trash piles have all kinds of bones, just not fish bones. Ours are/were full of fish bones, anywhere there's fish.
Your sources seem to wildly differ from my sources regarding the bulk of ancestral homo sapiens evolution during the ice ages. Feel free to share them.
As for the need for agriculture consider that single modern day hunter gatherer in Amazon forest can within few hours get enough starchy vegetables in a forest to feed at least 10 persons.
As for the need for agriculture consider that single modern day hunter gatherer in Amazon forest can within few hours get enough starchy vegetables in a forest to feed at least 10 persons.
Insanely speculative. Homo sapiens brains were largest 90k years ago, stayed there until 60k years ago, shrunk a little until ~10-15k years ago, then began shrinking markedly.
This coincides with a similarly slow transition from ice-age ~99%-carnivorous hunters (biggest brain), to hunter-gatherers (a little smaller, still big), to agriculture (begin massive shrinkage).
How do you get "starches" in any calorically significant quantity?
Oh yeah, agriculture is the name of the game.
But even all THIS "is rather speculative" as well: after all, bigger brain cannot just be equated to "smarter brain", either. Maybe starch allowed the brain to retain intelligence more efficiently and thus to shrink! Personally, I don't believe it, but frankly until we get a frozen ice-age homo brain, we won't have any way of knowing. Even then, it's just better-informed speculation.