Manners, especially "please" and "thank you", have a lot to do with anthropology. In hunter gatherer societies, it is commonly rude to thank someone. Hunter gatherer societies must share because resources like hunted animals are not very easy to depend on. This variability is reduced by sharing within tribes. You thank them because you do not completely EXPECT it of them. Today, thanking is sometimes used very differently. For example, "thank you for not smoking." Or to apologies without taking blame: "Thank you for waiting" ... um, my pleasure. Manners are commonly tools used to justify how our society works.