Today's topic is food/not-food. The concept of whether a particular food is edible or inedible usually is based in your own particular culture. To put it in simplest terms, "food" is what your mother fed to you as a child growing up. That is when your tastes form, and anything that varies too wildly from those tastes will usually inspire feelings of revulsion. Certain foods are touchstones of cultural identity because nobody else will eat them. The rest of the world considers them to be "not-food," and shuns them.
America is a melting pot culture, and we have long since appropriated things from other cultures, including cuisine, and made them our own. We took pizza and pasta from the Italians and tacos and burritos from the Mexicans and egg rolls and chow mein from the Chinese, although the American version usually differs significantly from the original. We did not, however, take haggis from the Scots or lutefisk from the Norwegians or seal blubber from the Inuit. Why? Because they varied too far from what most of us think of as food. And so, only a Scot will eat haggis, only a Norwegian will eat lutefisk, etc.
There are other culturally-linked food traits. For instance, in Europe, there is the split between southern areas where olive oil is used for cooking and northern areas where butter is used instead. I think that this may be due to the beneficial mutated gene that allows many northern and western European adults (and their descendants world-wide) to digest the lactose in cow's milk. Most of the adults in the rest of the world are lactose-intolerant, and this may be why goat's milk cheese is more popular in Greece, for instance. And while we in America would think nothing of offering someone a glass of cow's milk, in places like China, it would be akin to offering a drink from a spittoon. In China, cow's milk is not considered to be "food."
Sometimes dietary inflexibility can be fatal. For instance, in the book Collapse, Jared Diamond explains why the Inuit thrived in Greenland at the same time that Norse colonists in Greenland were starving themselves to extinction. The Inuit ate whale and seal blubber, as well as fish. The Norse, by contrast, raised grass in their fields for the hay needed to feed their cattle, as well as a few vegetables. Archaelogical studies of the middens (garbage heaps) of Norse Greenlanders indicate that they ate very little fish, which is odd considering that their cousins in Iceland and Norway ate a lot of fish. For some reason, their isolated culture had declared fish, seal and whale to be "not-food." And so they starved amid plentiful sources of food when the climate became too cold and the growing season too erratic to raise hay and maintain their cattle herds.
Mankind is endlessly inventive and often finds ways to convert not-foods into sources of food. For instance, cassava (or manioc) root, an important source of starch in much of the tropics, is poisonous in its raw form. It has to be treated to remove the cyanide. Almond trees originally had the same problem, but the domesticated variety, which yields "sweet" almonds doesn't have that problem. Wild undomesticated almond trees yield "bitter" almonds which also have high amounts of cyanide in them. One wonders how the ancients managed to come up with ways to make poisonous roots and nuts into edible food, and how many poisoned themselves trying to do it.