There's actual data on ancestral diets from preserved human bodies discovered in places like glaciers and anaerobic peat bogs. For example, here's a paper on t

There's actual data on ancestral diets from preserved human bodies discovered in places like glaciers and anaerobic peat bogs. For example, here's a paper on two Iron-Age bog bodies: "An archaeological interpretation of Irish Iron Age bog bodies (2013)" by EP Kelly > "Scientific analysis of the chemical constituents of the hair and fingernails provided information on the diets of the two men in the months preceding their deaths. Clonycavan Man had a plant-based diet for four months prior to his death, suggesting that he may have died during the autumn before the onset of a meat-rich winter diet. By contrast, Oldcroghan Man may have died in the winter or early spring, as he ate a diet with a substantial meat component during the four months prior to his death." Diets likely varied globally based on local conditions - seasonal variation was likely the dominant factor in food sources for people living in the mid-latitudes and polar areas (winter/summer) as well as in the tropics (wet/dry), and people near oceans would likely be eating ocean-sourced food. This was likely true for both nomadic hunter-gatherer groups as well as simple subsistence farmers and herders.