Nicholas Wade, the author of the book I mentioned before, does indeed place the rise of our species at about 55,000 to 45,000 years ago.  He does a very nice job of encapsulating the spread of humans around the globe.  (It seems that for thousands of years we were blocked from expansion by a couple of rival species in what is now the Middle East.  Go figure.)

But to find a single male to whom all currently living humans could trace ancestry requires a journey back of only 5,000 years.  At least to hear him tell it, and to see him do the math.  The idea is that all other lineages eventually either die out or intermarry & produce offspring with the descendants of that same great, great, great grandpappy.

[New Edit:  The more I thought about this, the more it failed to make sense.  Eventually I had to go to a nearby bookstore and find another copy of Wade's book to find my error.  It turns out that I need to read more slowly.  The numbers cited by Wade go like this:  About 50,000 years ago, an ancestral population of about 5,000, was the pool from which the one male ancestor came.  Thank you for the link to National Geographic's excellent site about prehistory.  --Herring405]

Mind you, this note is written from memory.  I loaned my book out as soon as I was done reading it, and I haven't seen it since.

Herring405