Current political correctness demands that "A person can't help his or her birth" must be changed to "A person can't help their birth." Marry Norris, in her book Between You and Me: Confessions of a Comma Queen, says this: "The colloquial use of "their" when you mean "his or her" is just wrong. It may solve the gender problem and there is no doubt that it has taken over in the spoken language, but it does so at the expense of number. An antecedent that is the singular ["a person"] cannot take a plural pronoun [their]. And yet it does, all the time--certainly in speech."