Free Catching Fire: How Cooking Made Us Human by Richard Wrangham Page B

hunter-gatherers, such as Andaman Islanders, Siriono, Mbuti, and Kalahari San, eat all their meat cooked. It is in cooler climates that people sometimes eat animal protein raw. If they are eaten uncooked, the raw items tend to be soft, like the mammal livers and rotten fish the Inuit eat. The island-living Yahgan in the south of Tierra del Fuego have three such foods, according to Martin Gusinde, who lived with them for twenty years. There is “the soft meat” of mollusks such as winkles, “squeezed out of the calcareous shell with a slight pressure of the fingers and eaten without any preparation, except that occasionally the little morsel of fish is dipped into seal blubber.” There are also the ovaries of sea urchins and the milky liquid in the shell, a delicacy shared by the Tlingit and eaten by Japanese and Europeans today in fine restaurants. According to Gusinde, a few individuals found the raw fat of a young whale tasty. Other than these cases, all animal protein was cooked.

    Game animals have a few soft parts. The Utes of Colorado were said to roast all their meat but they ate the kidneys and livers raw. Australian aborigines supposedly eat mammal intestines raw on occasion, as Inuit do with fish and birds. Raw intestines may seem a startling preference in view of the potential for parasites to be present. They are likewise almost always the first part of a prey animal eaten by chimpanzees, chewed and swallowed much faster than muscle meat.

    Raw-blood meals are well known among pastoralists such as Maasai, and as we saw in chapter 1, reported by Marco Polo in thirteenth-century Mongol nomad warriors. Elsewhere raw-fat meals are provided by fat-tailed sheep. Asian nomads value these sheep so highly and have bred them to such an extreme that they sometimes provide their animals with little carts to support the massive tail. On trek the nomads remove some of the fat for a raw meal, and the sheep travels a little lighter the next day.

    While some foods are naturally tender, meat is variable. Meat with smaller muscle fibers is more tender, so chicken is more tender than beef. An animal slaughtered without being stressed retains more glycogen in its muscles. After death the glycogen converts to lactic acid, which promotes denaturation and therefore a more tender meat. Carcasses that are left to hang for several days are more tender, because proteins are partly broken down by enzymes.

    But nothing changes meat tenderness as much as cooking because heat has a tremendous effect on the material in meat most responsible for its toughness: connective tissue. Composed of a fibrous protein called collagen and a stretchy one called elastin, connective tissue wraps the meat in three pervasive layers. The innermost layer is a sleeve called endomysium, which surrounds each individual muscle fiber like the skin of a sausage. Bundles of endomysium-enclosed muscle fibers lie alongside one another jointly sheathed in a larger skin, the perimysium. Finally, those bundles, or fascicles, are held together by the outer wrapping, or epimysium, which encloses the entire muscle. At the end of the muscle, the epimysium turns into the tendon. Connective tissue is slippery, elastic, and strong: the tensile strength of tendons can be half that of aluminum. So connective tissue not only does a wonderful job of keeping our muscles in place but it also makes meat very difficult to eat, particularly for an animal like humans or chimpanzees whose teeth are notably blunt.

    The main protein in connective tissue, collagen, owes its toughness to an elegant repeating structure. Three left-handed helices of protein twirl around one another to form a right-handed superhelix. The superhelixes join into fibrils, and the fibrils form fibers that assemble into a crisscross pattern. The effect is a marvel of microengineering. The extraordinary mechanical strength of collagen explains why sinews, or tendons, make excellent bowstrings and why it is the most