The root of the English posessive suffix "'s" was an unapostrophized -s ending for the genitive case. However, by about 1550, people thought is was an enclitic form of "his" — this being when it was proper to refer to everyone with what are now the male pronouns (which it ain't anymore, so don't). Where once people had called the boat belonging to David
Davids boat
they began to 'correct themselves' to say:
David his boat
which drifted along through
David 'is boat
to (as Industrial Revolution and literacy more or less standardized English)
David's boat.
"To", as a marker of infinitive verbs, is enclitic in spoken American English:
I want to ride my motorcycle
is often pronounced, & sometimes spelled:
I wanna ride my motorcycle
In everyday speech, I almost never say or hear "I'm going to go"; it's "I'm gonna go". Writing does eventually follow speech, so it's possible that this will be as accepted a spelling as "Beatrice's" in a hundred years.
This writup has benefitted from kind correction by Cletus the Foetus and http://www.quinion.com/words/qa/qa-pos2.htm