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 Ottoman Empire lasted 700 years. Holy Roman Empire, with all It's ebbs and Flows, (Mostly Flows) Lasted from 10th century to 18th century for almost 800 years. Eastern Roman Empire, (Byzantium) lasted for 1100 years though it was a Vassal and pale shadow of it's glory by the last part. And Ethiopian empire, the only African Nation to escape Western Dominance in Africa from 12th century to 20th century. 800 years till 20th century!