The whole idea of sun bathing is as well relatively recent, I believe going back to the early years of the past century and was anyway limited to very few.

And, as anecdata only - in the '70's - I was a child/kid and when we went to the seaside there were a few rules (carved in stone) by my granny:

1) you get to the beach no later than 8:00

2) you get out of the beach no later than 11:00

3) you can optionally go back to the beach no earlier than 16:00

4) for the first 15 days of holidays you stay under the tent/umbrella at all times except when taking a bath

But if you look at people who spend a lot of time in the sun professionally, they rely on long sleeve shirts and pants to protect themselves.

We survived winters without fur. Perhaps sunscreen isn't much different. Mud slathered on our bodies to avoid painful sunburns in Summer could've worked fine for 300,000 years just as animal hide and straw worked to avoid freezing to death in Winter.

But there may be more to it. I wonder if the intensity of the Sun and/or the strength of Earth's magnetic field could fluctuate more than current science has been able to determine.

Mankind evolved locally to handle sun, the problem is when your average pale as fuck northerner decides to go to Mallorca for 2 weeks in July

I still sunscreen the kids because they take their hats off all the time.