a very interesting question you've posted. As far as I know from personal experience and reading of psychology books, it's both. However, psychiatrists insist that it is nurture more than nature. They have studied subjects who could inherit schizophrenia and observed that those living in a positive environment did not develop this condition. Older generations here in Greece believed that it was devinitely inherited. I have seen situations where these beliefs came true, but in each case the environment was problematic.