Where do “new” humans come from? If all of us are re-incarnations of prior human beings, how do we account for the growing population? Where do “new” humans come from?
We are not necessarily re-incarnations of prior human beings. There are 31 planes of existence in Buddhism. So the  present human beings could result from any of the 26 planes out of 31 planes of existence(except 5 non-returner Bhrama realms) which consist of unaccountably large number of beings. For example, imagine the number of beings living in  Animals realm (tiracchana yoni).