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Observe, however, that the pupil is unnaturally sharp edged. That's because we have the pupil set to black. It should not be - it should have the iris color map applied.

I disagree completely. A pupil is a hole, an opening - there's nothing there. I think the key to getting a realistic pupil is to use no texture map, but to have a refractive and absorptive surface for it, for light to interact with it [more] naturally, along with a realistic lens and retina.
Well... maybe when we're all using Maxwell Render, that is. ;-)