Thanks so much for this post, William McKinley!
I disagree with Jonah Goldberg's above observation. That is, I do believe the Constitution is "alive," but not in the sense that the "living document" crowd avers. (If it were dead, America as we know it would also be dead.)
And I do believe that biologists have put forward criteria indicating life which, to me, clearly pertain to the Constitution. Perhaps the most important one is that any living entity is capable of making sensitive adjustments to changes in the environment (internal and external) in which it lives, while at the same time maintaining its own integrity and its identity.
When the Left says "living document," what they really mean is they want a document that can change into something else. Which is not what a living entity does at all: It wants to preserve itself.
FWIW