Explaining left and right

Davide Castelvecchi considers the problem of explaining the concepts of left and right, without diagramming and without reference to any shared experience (assume the listener is an alien and doesn't have the same experience as you). Castelvecchi describes how embedded in convention our concepts of left and right are. Of course those conventions are helpful in allowing us to diagram and share spatial information easily; schooling ensures most of us never challenge the use of right and left to show positive and negative values in graphs, for example. (Castelvecchi's working method is to purify and crystallize DNA and analyze its structure which will reveal a double helix twisted in such a way that it looks like a spiral staircase that goes up as it goes from left to right. Hardly a walk in the park.)
[Via NotExactlyRocketScience]