inborn (adj.)

a Middle English merger of Old English in (prep.) "in, into, upon, on, at, among; about, during;" and Old English inne (adv.) "within, inside," from Proto-Germanic *in (source also of Old Frisian, Dutch, German, Gothic in, Old Norse i), from PIE root *en "in." The simpler form took on both senses in Middle English.

Sense distinction between in and on is from later Middle English, and nuances in use of in and at still distinguish British and American English (in school/at school). Sometimes in Middle English shortened to i.

The noun sense of "influence, access (to power or authorities)," as in have an in with, is first recorded 1929 in American English. to be in for it "certain to meet with something unpleasant" is from 1690s. To be in with "on friendly terms with" is from 1670s. Ins and outs "intricacies, complications of an action or course" is from 1660s. In-and-out (n.) "copulation" is attested from 1610s.

Old English boren, alternative past participle of beran (see bear (v.)). The -en of the Middle English past participles tended to drop the -e- in some verbs, especially after vowels, -r-, and -l- , hence also slain, etc., Middle English stoln. "In modern use the connexion with bear is no longer felt; the phrase to be born has become virtually an intr. verb" [OED].

It is attested from early 14c. as "possessing from birth the character or quality described" (born poet, born loser, etc.). It is from 1710 as "innate, inherited;" the colloquial expression in (one's) born days "in (one's) lifetime" is by 1742.  The distinction of born from borne (q.v.) is 17c.