A most interesting article. One thing unmentioned was the relatively late appearance of the possessive its in English. It’s uncommon in Shakespeare who generally uses his or simply it. In the passage from Antony and Cleopatra below (II,vii) one can find in close proximity both its and it used as the possessive form.
What manner o’ thing is your crocodile?
It is shaped, sir, like itself; and it is as broad
as it hath breadth: it is just so high as it is,
and moves with its own organs: it lives by that
which nourisheth it; and the elements once out of
it, it transmigrates.
What colour is it of?
Of it own colour too.
It was around this time (late 16th/early 17th century) that its was spreading like wildfire. OED comments: (its, adj. and pron.)
The spread of its as possessive adjective seems to have been rapid in written sources from the late 16th cent. onwards, although it does not appear for instance in the Bible of 1611. (This does show it adj. 1 once (see quot. 1611 at it adj. 1), which was later altered, in an edition of 1660 and in later editions, to its.)
BTW the quotation referred to is 1611 Bible (A.V.) Lev. xxv. 5 That which groweth of it [1660 its] owne accord..thou shalt not reape.