It might be helpful if you specified which table manners you had in mind. Table etiquette is a cultural question, and varies markedly between cultures. A chopsticks culture has different etiquette from a hands culture has different etiquette from a fork and knife culture. In some cases this might have specific and identifiable origins, e.g. a number of Islamic practices are elaborated in the Hadith, while others might be more anthropological, e.g. cultural aversion to eating with the left hand has its roots in the left hand being the bathroom wiping/washing hand in cultures that don’t use toilet paper.