While UV rays can cause skin cancer, because skin cancer usually affects people after they have had children, it likely had little effect on the evolution of skin color because evolution favors changes that improve reproductive success.
The only problem was that I couldn't remember where I had heard that. In fact, I wasn't all that sure that I was right. I know that the Roman Empire lasted rougly 500 years but how about the Egyptians, the Chinese, the Ottomons, etc. I thought that it would be interesting to explore different empires and see how long they lasted. In another article, I talk about the definition of civilization..
The Eastern Empire lasted from A.D.395 to A.D.1453 under 94 emperors. From this you can see that the number of Roman emperors will be 147 if you count only the rulers of the United Roman Empire, or 9 less excluding rebel emperors, and many more if the Divided Empire totals of 23 and 94 more emperors are included.