Old English boren, alternative past participle of beran (see bear (v.)). "In modern use the connexion with bear is no longer felt; the phrase to be born has become virtually an intr. verb" [OED]. Distinction between born and borne (q.v.) is 17c. From early 14c. as "possessing from birth the character or quality described" (born poet, born loser, etc.). From 1710 as "innate, inherited;" colloquial expression in (one's) born days "in (one's) lifetime" is by 1742.
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.