cogtest

From an evolutionary standpoint, language is not that old. What is old, however, are feelings of gratitude and ways of expressing gratitude. The proximal reasons for saying "thank you" are mostly social - to fit in with our culture. When someone does something nice, (holding a door open for example) you repay the act of kindness by saying thank you. The ultimate reasons for saying thank you are found more in the acts of gratitude. You don't necessarily have to say thank you for someone to know you are thankful. On the other hand, there are people who say thank you and do not really mean it. In the past when someone wanted to repay an act of kindess they could have done so without actually using words (maybe by reciprocating the act later on). Over time, as language and culture developed the words did, too. There are even current studies that show gratuitous people live longer than non-gratuitous people.

I think that "thank you" is said because it is beneficial to us. By saying it, we are expressing gratitude for someone who has just done something for us, and we are also ensuring that we do not alienate that someone who perhaps in the future may do something for us again.

I think that saying "thank you" and other manners have been encouraged by cultures because they are vocal acknowledgements that someone has done something for you, indicating that you realize you are indebted to them. I think that "thank you" is almost like a primitive IOU which ensures to the benefactor that their favor has not gone unnoticed and they will therefore receive a benefit from it some time in the future. This would be the ultimate explanation for the existence of "thank you" in our society while the proximate explanation would be our fear of being ostracized for lacking proper manners.