Fat gain is sensitive to the ratio of consumed macronutrients like fats and carbohydrates. Confusion arises from simplistic focus on one nutrient at a time.
Obesity is positively correlated with polyunsaturated fat intake, but is negatively correlated with saturated fat intake over large intervals of modern history.
For some historical data on sugar intake trends, and fat:carb ratios over time, I recommend these two articles:
I have seen blogs (Brad Marshall) that American diet was very carb heavy in early 1900 and presumably before.
Since, then starch has gone down quite a bit but sugar has increased. Sugar intake in 1900 was not trivial.
In Europe too, carb intake was heavy in pre-industrial period.
One can derive the hypothesis that obesity is correlated with fat intake.
Obesity is positively correlated with polyunsaturated fat intake, but is negatively correlated with saturated fat intake over large intervals of modern history.
For some historical data on sugar intake trends, and fat:carb ratios over time, I recommend these two articles:
Sugar Has No Impact On Obesity: Just-so stories in metabolic health [https://mindandmatter.substack.com/p/sugar-has-no-impact-on-obesity-just]
Carbohydrate:Fat Ratios in Fat Gain & Obesity [https://mindandmatter.substack.com/p/carbohydratefat-ratios-in-adiposity?utm_source=publication-search]
I wonder about the oral health of Peaters.
I have heard that their teeth are not exactly what should be. Plus, sugar has to be pretty rare thing in Stone Age, not to mention Ice Age.
Wild fruits, the sort chimps eat, are fibrous and have substances like tannins.