Pardon my ignorance, but what does 20,000 kcal/day mean? They can’t be talking about calorie intake! Even i can’t eat that much! LOL!
That would make for some very tubby ancient people.
I will not be insulted if you correct me, because i really don’t know what it means and am just judging from context.
When you read a label that says 200 Calories (notice the capital letter) it actually means 200,000 calories (as the actual scientific definition of calorie = the energy needed to raise one gram of water one degree Celsius at one atmosphere of pressure), or 200 kilocalories. So food energy is generally measured in kcal, but called Calories.
We function on about 1,500-2,000 kcal/day now, in an extremely sedentary culture. I’d not be surprised at early cultures (as noted, “safe” ones where food was abundant & reliable, and threats rare) consuming several times that due to no transportation (for self nor goods), close involvement with farming & hunting, and labor-intensive everything every day all the time. Non-temperate weather also necessitates high calorie burn just to maintain safe body temperature, both in just existing and in actively managing environment (hauling wood to burn, wearing heavy animal hides, sweating profusely, etc.).
Today, Olympic athletes et al are known to burn upwards of 5,000kcal/day - and that’s concentrated activity surrounded by sedentary behavior (sitting while transported, other such relaxed behaviors). When every waking moment involves labor, I can see common folk burning that much easily.
I recall someone computing that a naked man just standing in a blizzard would need 30,000kcal/day to survive. That’s pretty extreme, yes, but does establish an upper limit to caloric intake; if you’re living Survivorman-like in extreme cold with primitive insulation & heat, you’re gonna be eating a LOT.
The 20,000 number may also cover _available_ calories. People may not have consumed/burned that much daily, but did have it available and may have reached that occasionally. Our current available calories are at least on par with that.
Just some thoughts; I’m no expert.