Ruddy foriegners coming over here, bringing their apostrophes

That is a formal description of the Saxon Genitive. Or in words,

In a nutshell, this graph can recognise:
- either noun + noun :
- or pronoun + noun:
- wives and childrens mouths -> <>
- anothers company -> .

I can only thank Odile Piton and Hélène Pignot for their enthralling monograph about the growth of the apostrophe in the English language. It appears the reason for all our confusions is that it is a foriegn import.

Explain's everything.