I have always had of the problem of sneezing when I see bright light, be it
the sun or a lightbulb or just some bright reflection.
I myself is of Chinese origin so I am not sure about the 'theory' that it is
more common in some ethnic groups.
It usually happens when I go from indoors to outdoors, that is, the sudden
projection of a relatively large amount of light onto the retina triggers
this. I have always explained it to myself that because the visual and
olfactory nerves are close together, an over-stimulation of one may affect the
other. As to its significance in evolutionary terms, I personally think that
it is a protective mechanism which prevents too much light from getting into
your eyes (which is potentially very damaging and may cause blindness) - this
is because when you sneeze you tend to close your eyes?
I have to say, though, that I have come across people who claim to have their
eyes open when they see so that they can keep their eyes on the road while
they're driving.
I don't know, perhaps what I'm saying is all utter rubbish, but that's what I
think, if I'm wrong, I'll be more than happy to receive criticism, afterall
this is what newsgroups are for, isn't it?