Anthropologists: Why do mulattoes like Obama and jews like Lieberman hide behind other colors and ethnicity's?

It is pretty silly to try and define someone as pure white or pure black. Jews are Caucasians but obviously not exactly the same as Celts or Germans. Germans look dark compared to me so is that supposed to make them and pretty much every one else on earth less of a Caucasian as well. Where should we draw the lines that divides races on the map. Obviously you can't so the whole distinction is rather meaningless. It is pretty stupid of Obama to call himself black when he was raised by his white mother. It is sad but racism is alive on both sides of the political spectrum. It has very little meaning in biology because the differences between the different races is so superficial.