You get a lot more sunlight in the tropics, so lighter skin is probably not as useful.
Indeed this is all just fun speculation.
“Indeed this is all just fun speculation.”
A lot of it is.
But it is true that light skin can be a negative in the tropics and dark skin a negative in cloudy cool higher latitudes.
Modern Man probably moved out of Africa about 150,000 years ago or so.
So there was plenty of time to develop into lighter skinned Euopeans or even some eastern Asians who have light complections in the winter and darker complections in the summer.
But the differences between Black Africans, Caucasians, Autralian natives, North Americans and Asians go a lot furher than skin pigmentation, althoug in the big picture, all human beings are far more closely related genetically than racists of any color would care to believe.
In geological time, 150,000 years is the blink of an eye.