This really shouldn't be some surprise. You probably do it on a regular basis without noticing. Shakespeare uses it in Hamlet: There's not a man I meet but dot

This really shouldn't be some surprise. You probably do it on a regular basis without noticing. Shakespeare uses it in Hamlet: There's not a man I meet but doth salute me As if I were their well-acquainted friend English has always used the singular they, especially (but not always) when the gender of the target of the pronoun is unknown.