ARRATOR: There is no question that individual human beings are different, one from the other. Our eyes confirm this day in and day out. Skin color. Body shape. Hair form. Eye shape. For several hundred years we have used these visual differences to classify people into four or five groups we call races.
PILAR OSSORIO, Legal Scholar / Microbiologist: We have a notion of race as being divisions among people that are deep, that are essential that are somehow biological or even genetic, and that are unchanging - that these are clear cut distinct categories of people.
RICHARD LEWONTIN, Evolutionary Geneticist: And the beauty of the race business is that you can identify people by just looking at them. You don't even have to look at their genes because one manifestation of their genes is there - namely skin color or eye shape or hair shape - and then that's the key to everything.
NARRATOR: The idea of race assumes that simple external differences, rooted in biology, are linked to other, more complex internal differences. Like athletic ability. Musical aptitude. Intelligence. This belief is based on the idea that race is biologically real.
OSSORIO: All of our genetics now is telling us that that's not the case. We can't find any genetic markers that are in everybody of a particular race and in nobody of some other race. We can't find any genetic markers that define race.