Converting base figures for ethnicity can, from what I understand, be a daunting task.  Take the Native Americans.  The ony commonality is the epicanthic fold at the eyes. The rest is dictated by the Tribal genetics.  Getting that "Roman Nose" and high cheek bones, from those I've worked with in the past on such efforts, can be horribley frustrating.

If one were truly interested in ethnic diversity, I would recommend using the Smithsonian archive of photography and looking at the earliest photos availabe of each ethnic group.  Consider the bone structure as an overlay for tweaking the geometries of the head and face for a more correct structure.

I've been told it can be time consuming, but I would feel it worth the effort.  Sadly, working two jobs (one of which is as a full time Instructor at the local University), I have not had the time and energy to learn any of the modeling programs and must rely on the kindness of those who DO work with them.

Take heart, diversity is out there...it's just going to take some work to make it visible to the average viewer.