Let me start off by saying, that I know that cutting hair and nails on shabbos is prohibited. My question is, is it a biblical or rabbinical prohibition. In my mind it seems rabbinic because when you look at the melacha of gozez (shearing) and look at what purpose they did it in the mishkan, they sheared wool and other materials off livestock to make clothing curtains and other items. Regarding cutting hair and nails however you usually throw them in the garbage. So wouldn't cutting hair and nails be a מלאכה שאן צריכה לגופה?