If you were able to steadily forage a pound of food an hour and it had 250 calories per pound, it might take you ten hours just to break even on your calories for the day. But if you were gathering something with 500 calories a pound, you could be done foraging in five hours and spend the next five focusing on your wall paintings. So the greater the energy density, the more calories per pound, the more efficient the foraging. We developed an acute ability to discriminate foods based on calorie density and instinctively desire the densest.
