Our ancestor, homo erectus, lived in caves, and is therefore informally called a "caveman." At some point, cavemen learned how to control and use fire. This was a tremendous breakthrough, affecting their behavior, their diet, and their evolution.

          Protection: The fire burning at the mouth of the cave was a barrier that predatory animals could not penetrate. The smoke discouraged parasitic insects.
          Heat: The fire kept the cave warm and dry. The ability to warm the cave facilitated the colonization of territories with a colder climate.
          Light: The fire lit up the cave, so that activity was no longer restricted to the hours of daylight.
          Cooking: Cooked food was tastier and easier to digest. It was also safer, since the heat killed parasites and food-poisoning bacteria that might be present. Cooking neutralized the toxins in some seeds, such as linseed, cassava, and manioc. Roots and tubers, inedible when raw, were added to the diet.
          Nutrition: Cooking made the carbohydrates in roots and tubers available. Cooking meat made it more digestible and made more of its protein content available
          Evolution: The brain is the organ that consumes the most calories. Cooked food increased the amount of nutrient available for the ongoing expansion and evolution of the human brain.

Thus, in every way, the attainment of the control of fire constituted a giant leap forward for the cavemen, on their way to becoming human.

Now suppose that by some miracle a modern human could visit the cavemen and communicate with them. This highly evolved homo sapiens could give them the benefit of millennia of accumulated knowledge. But suppose that the human who had this miraculous opportunity was a vegan. He or she would lavish the following pearls of wisdom upon them:

          Fire: Burning fuel releases greenhouse gases into the atmosphere and contributes to global warming.
          Smoke: A fire releases smoke into the atmosphere and causes air pollution.
          Meat: Animals have rights as well as humans. Therefore, humans should not exploit animals. It is immoral to eat products derived wholly or partly from animals.
          Fats: Animal products contain harmful cholesterol, which is detrimental to human health.
          Cooking: When fats, carbohydrates, and proteins are heated, dangerous chemicals are produced. Cooking destroys important nutrients, vitamins, and fibers. It is healthier to eat uncooked food.

If vegetarians eat vegetables, what do humanitarians eat?