A good friendship is priceless - but it appears to be almost timeless as well.
Researchers suggest that being close to others with similar personality traits goes back millions of years.
They found the phenomenon occurs not only in people but also in chimpanzees. This indicates its origins date to when humans and the apes had a similar evolutionary path before going their separate ways.
The last common ancestor of chimps and humans lived at least six million years ago, indicating the first 'best friends' walked the Earth all that time ago, said Austrian and Swiss researchers.
They studied colonies of chimpanzees in two Dutch zoos and firstly rated their personality traits.