My guess is that the proto-Indo-European kw- sound turned into hw- in the old Germanic languages. In Old English, most modern wh- words were spelled with hw. Looks like the h and the w reversed order at some point. For example:
what - hwæt
why - hwý
who - hwá
which - hwlilc
when - hwonne
where - hwǽr
whether - hwæðer
whom - hwǽm

erinja:My guess is that the proto-Indo-European kw- sound turned into hw- in the old Germanic languages. In Old English, most modern wh- words were spelled with hw. Looks like the h and the w reversed order at some point. For example:
what - hwæt
why - hwý
who - hwá
which - hwlilc
when - hwonne
where - hwǽr
whether - hwæðer
whom - hwǽm

Yeah, Grimm's law and strange English spelling FTW! Haha. Regardless, I wonder if that knee-jerk breathy hum sound of curiosity had some influence on making nasal and velar question words, maybe the Germanic languages semi-reflexed on a pre-Indo-European form.

Quick, to the time machine! 7,000BC, here we come! (could get hairy if it turns out the view of god creating the world 6,000 years ago is indeed true!)