I am no musician, but based on what I understand, a musical scale is an arrangement of a set of notes (pitches/ frequencies) within an octave (a mathematically repeatable range). Most of us have heard about the Heptatonic scale with seven pitches. It seems that the Pentatonic scale with five pitches is something that we are naturally attuned to (even a child inherently finds it easier to understand).
Most TED videos are really cool. They have added a section called the 'Best of the Web' and this one featuring Bobby McFerrin is simply amazing. Most of us know of Bobby McFerrin through his wonderful song 'Don't worry, be happy' (click on this wiki link to read more about this song's Indian connection) with a video featuring Robbin Williams, which won the Song of the Year Grammy in 1989. In the following video, he demonstrates how natural the pentatonic scale is to the human mind.
The following is the YouTube video: