[dualogy]

> Of cause this is rather speculative

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.