The Bumps

Wikipedia is useless. We've just been wondering where the ritual of giving someone The Bumps on their birthday come from from. Like any thorough journalist I went immediately to Wikipedia and it told me diddly-squat.

But where did this strange custom come from. Is it a form of torture that has become a children's game? I don't know. The internet has failed me. 

I asked BBC History but they're not taking my request seriously. 

Can anyone out there help?