People rarely say thank you when others help them out, scientists say

It's not to do with rudeness, but with tradition: we take it for granted that people will cooperate with each other

At first glance it seems a slight on the polite: recordings of more than a thousand casual conversations from around the world reveal that people hardly ever say "thank you" when others help them out.

The everyday social exchanges, which played out in eight different languages on five separate continents, highlight a global reluctance to acknowledge trivial favours, such as passing the salt. Overall, people expressed their thanks only once in every 20 occasions.