Protect the face and the neck, when the sun is powerful and the risk of burning is high.
> How did we get through the Neolithic Era without sunscreen?
Actually, perfectly well. It's modern times. We optimize for long individual lives, not propagation of the species. As lifespans increase, so should efforts to avoid cumulative, damaging radiation.
Similarly, heavy meat consumption gave early humans an advantage, but you shouldn't adopt that caveman behavior for a 100-year lifespan - it doesn't "work" at that scale.