As recent studies have revealed, we can’t really know what our ancestors ate with 100% certainty, and there is undoubtedly a huge variation amongst different populations. For example, we have the traditional Inuit and the Masai who ate a diet high in fat (60-70% of calories for the Masai and up to 90% of calories for the Inuit), but we also have traditional peoples like the Okinawans and Kitavans that obtained a majority (60-70% or more) of their calories from carbohydrate. So it’s impossible to say that the diet of our ancestors was either “low-carb” or “low-fat”, without specifying which ancestors we’re talking about.