David Shariatmadari looks at several of the reasons English has shifted, both in [spelling and pronunciation](http://www.theguardian.com/commentisfree/2014/mar/11/pronunciation-errors-english-language):
> A dark “l”, in linguistic jargon, is one pronounced with the back of the tongue raised. In English, it is found after vowels, as in the words full or pole. This tongue raising can go so far that the “l” ends up sounding like a “w”. People frown on this in non-standard dialects such as cockney (“the ol’ bill”). But the “l” in folk, talk and walk used to be pronounced. Now almost everyone uses a “w” instead- we effectively say fowk, tawk and wawk. This process is called velarisation.
Other times, sounds swap around and change the word dramatically:
> Wasp used to be waps; bird used to be brid and horse used to be hros. Remember this when the next time you hear someone complaining about aks for ask or nucular for nuclear, or even perscription. It’s called metathesis, and it’s a very common, perfectly natural process.
I found the whole article inneresting.