If you’re truly interested in consuming the original Primal brain food, look no further than bone marrow: perhaps the first reliable source of large, fatty animal products our scrappy ancestors were able to procure. Yes, before we became spear-using cunning tacticians surrounding, stalking, and out-maneuvering large prehistoric ungulates, we feasted on the bones of fallen prey. Or, more accurately, we feasted onwhat lurked insidethe bones (and the skulls, for that matter).Animal fatand protein improved the quality of our diet by making digestion less energy intensive. Bone marrow, especially, was highly caloric and nutrient dense, allowing early human ancestors to divert metabolic resources away from the costly digestion of roughage and toward bigger, costlier brains. This spurred the increase in hominid brain size that we still enjoy today.