"we survived for thousands of years stark naked without sunscreen and vitamin suplements" We also ate differently in the Stone Age, so our vitamin intake might

"we survived for thousands of years stark naked without sunscreen and vitamin suplements" We also ate differently in the Stone Age, so our vitamin intake might have been different. Finally, life expectancy in the Stone Age was much shorter. Even excluding infant deaths, few people lived long enough to get cancer. Cancer is a typical disease of old age.