J-WO
Author of 'Pennyblade' and 'Feral Space'
Vitamin D production depends on sunlight, not temperature. If they were living in the location of modern Spain/Greece etc, why would they be any less dark than the current inhabitants of those lands?
True enough for those in Greece and Spain, but what about the more northerly climes? What applied to Homo Sapiens spreading across Europe would surely apply to Neanderthal. And I imagine the Ice ages cloud cover would preclude a lot of sunlight as well as temperature.
On the other hand, I might be missing something. I'm no expert on any of this.