>what our biologically identical ancestors ate for a huge multiple of time longer than the modern western diet.
Why is there a belief that our ancestors had a singularly common diet? Humans have lived in all areas of the earth with vastly different diets. Some were high in fat, some were high in protein, some relied on plants/fruit, others were more balanced, etc.
Yes we probably on average have a higher carb intake than most humans in the past. But that doesn't mean there was some standardized diet that all pre-historic humans ate. They ate whatever was around to survive.
Many of the staples of the Western diet simply haven't been around for longer than 15,000 years (agriculture), many in fact less than 100 years (heavily processed foods). It's not about ancestors all eating the same thing; it's about the fact we've introduced tons of new things, some we can handle and some we can't (and it probably varies per person).
The issue is not much about what was there, it's what wasn't. Fruits, vegetables, meat of some form was pretty much distributed all around (yes, in different quantities, etc, still)
And sure, the evolutionary pressures were huge. This seems to be the source of things like lactose tolerance (the default is intolerance)
The modern western diet is mostly made of vegetable oils, caffeine containing leaves and beans, huge amounts of refined sugar, ridiculous quantities of grains, antibiotic infused meats, fruit juices, milks, fermented products, huge amounts of corn syrup. Its no great challenge to go to the store for groceries and come home with nothing not on the list above, yet almost none of it existed more than a couple centuries ago. I realize this is considered an incredibly controversial opinion; I assume "most people" strongly believe our ancestors in 8000 BC mostly ate McDonalds and drank MtDew for every meal.
Why is there a belief that our ancestors had a singularly common diet? Humans have lived in all areas of the earth with vastly different diets. Some were high in fat, some were high in protein, some relied on plants/fruit, others were more balanced, etc.
Yes we probably on average have a higher carb intake than most humans in the past. But that doesn't mean there was some standardized diet that all pre-historic humans ate. They ate whatever was around to survive.