This didn't really turn out to be a response to razib's post below, so I'm giving it its own topic instead of posting a comment.

Two good papers on Multiregional evolution are Wolpoff's Population Bottlenecks and Pleistocene Human Evolution and Modern Human Ancestry at the Peripheries: A Test of the Replacement Theory.

My conception of Multiregional evolution is this: You have a widespread Homo species that maintains enough genetic interchange to avoid specification except in isolated instances. Combined with that (and this is purely my own speculation) is possibly a universal selective pressure towards larger brain size and a couple of other things. This selective pressure is present due to the new adaptation of long infancy periods. Before that, large brain size was somewhat maladaptive because of the dangers of childbirth.

The main evidence for Multiregional evolution seems to be regional fossil characteristics present in what should be different species. This is interpretive, so there are reasons to be skeptical.

On the other hand, the evidence for Out of Africa is based on genetic models that I have always been a little skeptical of as well. There is a type of model that does not respond well to any added complexity. Unlike razib, I like my beautiful simplicity in fundamental physics – anywhere else and it strikes me as out of place.

The weight of the evidence is behind Out of Africa, I think, but I read whatever I can on the Multiregional theory.