If you have some time, check out this piece (in three parts) by Errol Morris, a New York Times blogger:
Which Came First, the Chicken or the Egg? (Part One)
Which Came First? (Part Two)
Which Came First? (Part Three): Can George, Lionel and Marmaduke Help Us Order the Fenton Photographs?
The last part gets a bit long but its nice seeing someone else wrapped in the unrelenting grips of obsession sometimes.