How do you know they went out during the day and weren't completely or mostly nocturnal?

Within living memory, Americans wore hats pretty much whenever they were outside. If we decide to give up sunblock, we might want to reconsider the change in fashions that got rid of them.

That's a relatively recent phenomenon in human history as well. What about the middle ages? What about the bronze age?

Yeah... let's live like we did in the middle age. Lifetime expectancy was HUGE.

“There is a basic distinction between life expectancy and life span,” says Stanford University historian Walter Scheidel, a leading scholar of ancient Roman demography. “The life span of humans – opposed to life expectancy, which is a statistical construct – hasn’t really changed much at all, as far as I can tell.

Life expectancy is an average. If you have two children, and one dies before their first birthday but the other lives to the age of 70, their average life expectancy is 35.

That’s mathematically correct – and it certainly tells us something about the circumstances in which the children were raised. But it doesn’t give us the full picture. It also becomes especially problematic when looking at eras, or in regions, where there are high levels of infant mortality. Most of human history has been blighted by poor survival rates among children, and that continues in various countries today.”

https://www.bbc.com/future/article/20181002-how-long-did-anc...

Adjust for infant mortality, war, etc., humans are still humans.

You realize hunter-gatherers exist today, right? They go out during the day and are not mostly nocturnal. They're found all over the world.

Because it's obvious to anybody. It's also obvious that modern humans are far less exposed to UV than our ancestors, who pretty much lived like current days hobos spending most of their time on fresh air.

Our human ancestors were not nocturnal. Sleep patterns were probably different, sure, but they went out during the day to gather and hunt for food.