Why would it be odd? And the fossil record shows a change in skeletal structure that fits with a digestive system shift from one better at digesting plants to one better at digesting animal protein and fat.
We also know that grain cultivation started about 12,000 years ago. So there's that.
Sure--Nutrition science organizations recommend fiber. But look at the history of those nutrition science groups and you'll find they were funded or founded by the Seventh Day Adventist Church. They push a vegan diet to save our souls not our lives. The science behind fiber points to us not needing it. The USDA recommends we eat fiber while also acknowledging we don't really need any.
And, no--no reputable body of nutrition science will tell you carbohydrate is essential (not sure what "pretty much essential means in this context--from a nutrition science pov, a nutrient is either essential (we need to eat it) or non-essential (we don't need to eat it); carbohydrate is clearly a non-essential nutrient. Many organizations recommend we eat carbs daily while also acknowledging that we don't need any carbohydrate in our diet.
I don't know why you say "ketosis is for survival." You seem stuck with the carbohydrate-is-essential mindset. But carbohydrate is NOT essential to our diet. Ketosis is a natural state one enters when they don't eat a lot of carbohydrate. Period.
I never recommend people go on a very-low-carb diet (VLCD). I provide information on what happens inside the body when one eats a VLCD. And I frequently point out that one should discuss a desire to go on a VLCD with one's doctor before doing so.
There is no proof that the brain needs glucose. And it's likely we will never have proof as to test the theory, we would need to rid the body of glucose--which would kill off the red blood cells that provide oxygen to the brain. But that's not why I considered you anthropomorphizing cells in the body--that came from you saying cells "preferred" glucose over other nutrients as a substrate for ATP production. Cells work on a substrate or they don't. They use what they are given. Period. No desire, no preference.
It's true that the brain will use glucose. It's also true the brain will use ketone bodies.
I don't get how you connect gluconeogenesis (the synthesis of glucose from fat and protein) with the invalidation of my argument. As I've acknowledged, the body does need some glucose--at a minimum, for metabolism inside red blood cells (which lack mitochondria). Glucose is the only nutrient red blood cells can metabolize. This need can be satisfied by the synthesis of glucose by the liver (via gluconeogenesis). This will happen when no digestible carbohydrate is eaten, or, if not enough is eaten to satisfy the demand. Other than that, we know that under conditions of a zero-carb diet, glucose produced by the liver will also be used by parts of the brain (although this doesn't prove that those parts can only use glucose--it just proves that the liver makes enough glucose to supply the red blood cells with some left over that gets used by the brain. If I had to guess, I'd say that the body evolved to over-estimate the demand from red blood cells (which would have a survival advantage) and the brain takes up the rest.
Like most poisons, the toxicity is in the dosage. Clearly, the body won't poison itself synthesizing too much glucose. And in what way should I reconsider my diet--I eat a VLCD now and have for the past 3 years. I'm down over 150 pounds and all my blood and urine markers are excellent (including my fasting glucose and insulin). I'm the healthiest I've been on 40 years.
You might find it helpful to add this to your reading list:
Biochemistry, (9th edition, Berg, et al) Macmillan International.
