To form the negative sentence, I used the present perfect tense, which requires the auxiliary verb "have" followed by the past participle form of the main verb. The negative form of "have" is "haven't" or "have not". In this case, the past participle form of "bear" is "born". Overall, "Bear hasn't been born" conveys the idea that the act of being born did not happen in the past for the subject, "bear".
In summary, "Bear hasn't been born" transforms the past participle form of "bear" into a negative sentence by using the present perfect tense and the negative form of the auxiliary verb "have".