Genesis seems to be one big mesh - no groups. Does this mean that each weight map (per joint) must include data for every single vertex in the whole figure. ...

***Probably not. Standard weight mapping for a joint only affects the area it affects. There would be no need to hold the weights for the toes in a finger joint.  ***

Right but what I'm failing to understand is how is a vertex or polygon is distinguished as being a part of the toe versus the head or whatever if there are no body part groups? If it is all one group, how is the association of a subset of the geometry with a joint implemented?

In the absence of any grouping, all vertices are eligible for rotation by any joint and a weight must be recorded for all of them.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)