If you think sitting up straight and keeping your elbows off the table is a bother, be grateful you weren't a child of America's early settlers. Back then, children didn't even get to sit at the table. They stood behind the adults and ate whatever was handed to them.
Later, children were allowed to sit at the table, but they couldn't speak unless an adult spoke to them. They couldn't ask for a dish, either. They had to wait until a grownup offered it to them. It was also considered rude to fidget, sing, or look at someone else who was eating.
Table manners are even older than tables. About 9,000 years ago, people cooked soups in pots. They dipped spoons of wood or bone into the cooking pot to eat. The first rules about eating determined who could dip into the pot first. Today some Inuit families in the Arctic still follow the tradition of eating from a common pot. Men get to dip in first, then women and children. Sometimes they don't use spoons. They just pick out pieces of meat with their fingers.
Eating with the fingers is a common custom. For about a thousand years, Romans and Greeks ate while lying on their sides on couches, with their heads pointed toward the table. One hand propped them up, the other handled the food. The Roman Empire finally fell in AD 476, and reclining dining customs disappeared as well.
Eating with the fingers never disappeared. Some Arab families still follow this custom. They use only the first three fingers of the right hand. In northern India, some diners use only the fingertips of the right hand, but in the south both hands are OK. In fact, far more people eat with fingers or chopsticks than use forks and spoons. But everyone has rules about eating politely.