On Courtesy, Reciprocity and the Maintenence of Society

It seems that people are generally a rather selfish lot. Most people don't do kind acts without some sort of recognition or reward, and you could get into a whole debate on the question of whether or not there truly is a selfless act (as shown in the episode of Friends).
The problem is that society is contingent upon people cooperating, working together, and helping each other out, at least from time to time.
Living in the city for the past year I've been observing people, especially on the bus and in cars on the road. People in transit seem to me to be especially selfish. (Too many rats in a cage perhaps.) Anyhow, when someone makes a kind or helpful act in these places, it stands out all the more. I'm thinking of the little acts that are so easy to do, that really take no time and effort at all, such as waving thankyou to the person who lets you in, or offering your seat to someone who needs it more than you do. These small acts are so easy to do, and yet they can really make a difference! (as cheesey as that sounds).
Social interactions are a lot like dominos. One person makes a nice gesture, and then the other person might pass it along to someone else! The person receiving the nice action my realize how nice and helpful it was, and be insprired to do it for someone else. Similarily, something as easy as saying thankyou and acknowledging someone who perhaps held the door for you or let you into a busy line of traffic may be enough to encourage the person to do it again for another.
On the other hand, just the opposite can happen. If someone doesn't get recognition for a kind act, or continually finds them self the giver but never the receiver, they are after every occurance all the more likely to stop handing out kind acts. If all hell breaks loose in this social courtesy degeneration, society will crumble into a heap of selfish atomized individuals all pushing and shoving as they run the rat race.
It's so simple and easy to both acknowledge people's acts of consideration and partake in passing out the kind acts. It just might make the world we live in a slightly friendlier place. So please people, take a little time out of your day to do something nice, or at least acknowledge the person who does something nice for you!